Other articles

1. NACA-RM-E56B23

   "This criterion, unavoidably subjective in nature, caused considerable scatter in the data"

   "Heat Requirements for Ice Protection of a Cyclically Gas-Heated, 36° Swept Airfoil with Partial-Span Leading-Edge Slat" ¹

   

   SUMMARY

   Heating requirements for satisfactory cyclic de-icing over a wide range of icing and operating conditions have been determined for a gas-heated, 36° swept airfoil of 6.9-foot chord with a partial-span leading-edge slat. Comparisons of heating requirements and effectiveness were made between the slatted and unslatted portions of the airfoil. Studies were also made comparing cyclic de-icing with continuous anti-icing, and cyclic de-icing systems with and without leading-edge ice-free parting strips. De-icing heat requirements were approximately the same with either heated or unheated parting strips because of the aerodynamic effects of the 36° sweep angle and the spanwise saw-tooth profile of leading-edge glaze-ice deposits. Cyclic de-icing heat-source requirements were found to be one-fourth or less of the heat requirements for …

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2. NACA-RM-E54I03

   "Ice formation on the unheated leading edge, which may occur prior to activation of the heating system, was removed in 1 to 1 1/2 minutes by a hot-gas-flow rate that would be sufficient for normal anti-icing."

   "Investigation of Porous Gas-Heated Leading-Edge Section for Icing Protection of a Delta Wing" ¹

   

   Abstract

   SUMMARY

   A tip section of a delta wing having an NACA 0004-65 airfoil section and a 60° leading-edge sweepback was equipped with a porous leading-edge section through which hot gas was bled for anti-icing. Heating rates for anti-icing were determined for a wide range of icing conditions. The effects of gas flow through the porous leading-edge section on airfoil pressure distribution and drag in dry air were investigated. The drag increase caused by an ice formation on the unheated airfoil was measured for several icing conditions. Experimental porous surface- to free-stream convective heat-transfer coefficients were obtained in dry …

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3. NACA-RM-E53C27

   "... quick and reliable shedding of dangerous leading-edge ice caps and good heat utilization."

   "Comparison of Several Methods of Cyclic De-Icing of a Gas-Heated Airfoil" ¹

   

   Abstract

   Several methods of cyclic de-icing of a gas-heated airfoil were investigated to determine ice-removal characteristics and heating requirements. The cyclic de-icing system with a spanwise ice-free parting strip in the stagnation region and a constant-temperature gas-supply duct gave the quickest and most reliable ice removal. Heating requirements for the several methods of cyclic de-icing are compared, and the savings over continuous ice prevention are shown. Data are presented to show the relation of surface temperature, rate of surface heating, and heating time to the removal of ice.

   Discussion

   INTRODUCTION

   The advent of high-speed, all-weather, jet-powered aircraft has emphasized the need for ice-protection systems that are light-weight, dependable, and automatic and that impose the least possible penalty on over-all aircraft performance. Anti-icing systems that evaporate …

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4. NACA-TN-3143

   "Very few data are available on the physical properties of ice formations having a density other than that of clear, solid ice"

   "Experimental Determination of Thermal Conductivity of Low-Density Ice" ¹

   

   Abstract

   SUMMARY

   The thermal conductivity of low-density ice has been computed from data obtained in an experimental investigation of the heat transfer and mass transfer by sublimation for an iced surface on a flat plate in a high-velocity tangential air stream.

   The results are compared with data from several sources on the thermal conductivity of packed snow and solid glaze ice. The results show good agreement with the equations for the thermal conductivity of packed snow as a function of snow density. The agreement of the curves for packed snow near the solid ice regime with the values of thermal conductivity, of ice indicates that the curves are applicable over the entire-ice-density range.

   Discussion

   This publication is included in …

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5. NACA-TN-2212

   "in icing conditions, periodic attempts should be made to throwoff the accretions by increasing propeller speed."

   "The Effect of Ice Formations on Propeller Performance" ¹

   

   Abstract

   Measurements of propeller efficiency loss due to ice formation are supplemented by an analysis to establish the magnitude of efficiency losses to be anticipated during flight in icing conditions. The measurements were made during flight in natural icing conditions; whereas the analysis consisted of an investIgation of changes in blade-section aerodynamic characteristics caused by ice formation and the resulting propeller efficiency changes. Agreement in the order of magnitude of efficiency losses tobe expected is obtained between measured and analytical results. The results indicate that, in general, efficiency losses can be expected to be less than 10 percent; whereas maximum losses, which will be encountered only rarely, may be as high as 15 or 20 percent. Reported. losses larger than 15 or 20 percent, based …

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6. NACA-RM-E53A22

   "radome icing has serious effects on the radar operation"

   "An Analytical Study of Heat Requirements for Icing Protection of Radomes"

   

   Abstract

   The heat requirements for the icing protection of two radome configurations have been studied. over a range of design icing conditions. Both the protection limits of a typical thermal protection system and the relative effects of the various icing variables have been determined. For full evaporation of all impinging water, an effective heat density of 14 watts per square inch was required. When a combination of the full evaporation and running-wet surface systems was employed, a heat requirement of 5 watts per square inch provided protection at severe icing and operating conditions.

   Discussion

   INTRODUCTION

   Radar is becoming of increasing importance in the design and operation of aircraft. Successful operation of these aircraft demands that the performance of the radar system including the radome be unimpaired by environmental factors including …

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7. NACA-RM-E7H26a

   "The current use of improved airplane ice-prevention equipment has extended operations in icing conditions and thus accentuated the need for protecting aircraft antennas against structural failures resulting from ice accretions"

   "Determination of Aircraft Antenna Loads Produced by Natural Icing Conditions" ¹

   

   Abstract

   A flight investigation was made to determine the effect of distance flown in the icing region, antenna length, and antenna angle on the tension occurring in aircraft antennae while in regions of aircraft icing.

   The, experimental antennas were of lengths ranging from 15 to 43 feet and were placed at angles of 0° to 64° with the airplane thrust axis. Distances up to 256 miles were flown in diverse icing conditions at true airspeeds from 157 to 214 miles per hour and pressure altitudes at which icing conditions were encountered.

   The results indicate that: The effect of ice formation on antenna tension increased with the angle of the …

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8. NACA-RM-SE9D20

   "After 7 minutes of icing, however, one antenna element experienced a vibratory failure"

   "Vibration and Investigation of CAA Type V-I09 Very-High-Frequency Aircraft Antenna" ¹

   

   Abstract

   Vibration and icing determinations on a CAA type V-109 very- high-frequency aircraft antenna were conducted in the NACA Lewis icing research tunnel. The antenna is an omnidirectional-range unit that consists of two aluminum elements mounted in a streamline plastic head forming a V in plan view with an apex angle of 80°.

   Vibration determinations during a nonicing experiment produced element-tip total amplitude of approximately 1/4 inch at a tunnel-air velocity of 300 miles per hour.

   During the icing investigation, a total amplitude as great as 7 inches was observed at the antenna-element tips with tunnel-air velocities greater than 160 miles per hour and a tunnel-air temperature of 20° F. At the higher tunnel-air temperatures, which produced a heavier and more severe ice accretion, the …

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9. Radomes and Antennas

   "The current use of improved airplane ice-prevention equipment has extended operations in icing conditions and thus accentuated the need for protecting aircraft antennas against structural failures resulting from ice accretions"

   

   These reviews are for studies of the effect of ice on radomes and antennas.

   • Gowan, W. H., Jr.: Vibration and Investigation of CAA Type V-I09 Very-High-Frequency Aircraft Antenna. NACA-RM-SE9D20. 1949.

     "After 7 minutes of icing, however, one antenna element experienced a vibratory failure"
     > review: NACA-RM-SE9D20

   • Kepple, W. L.: Determination of Aircraft Antenna Loads Produced by Natural Icing Conditions. NACA-RM-E7H26a, 1948.

     "The current use of improved airplane ice-prevention equipment has extended operations in icing conditions and thus accentuated the need for protecting aircraft antennas against structural failures resulting from ice accretions"
     > review: NACA-RM-E7H26a

   • Lewis, James P., and Blade, Robert J.: Experimental Investigation of Radome Icing and Icing Protection. NACA-RM-E52J31, 1953.

     "At present very little is known of the effect of radome …

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10. NACA-RM-E55E17a

    "rain deflection by jet blast appears feasible for flight speeds"

    "Preliminary Data on Rain Deflection from Aircraft Windshields by Means of High Velocity Jet-Air Blast" ¹

    

    Abstract

    A preliminary experimental investigation is being conducted to determine the feasibility of preventing rain from impinging on aircraft windshields by means of high-velocity jet-air blast.

    The results indicate that rain deflection by jet blast appears feasible for flight speeds comparable with landing and take-off speeds of interceptor-type jet aircraft; however, attainment of good visibility through the mist generated by raindrop breakup presents a problem. For the simulated windshield and the lower windshield angles used in the investigation, air-flow rates of the order of 3.3 pounds per minute of unheated air per inch of windshield span were required for adequate rain deflection at a free-stream velocity of 135 miles per hour.

    A method has been devised whereby it is possible to produce large-diameter …

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11. NACA-TN-2855

    "For practical application ... the discharging of heated jets into an air stream requires knowledge of the temperature profiles downstream of the heated jet and of the depth of penetration"

    "General Correlation of Temperature Profiles Downstream of Heated Air Jet Directed at Various Angles to Airstream" ¹

    

    Abstract

    An experimental investigation was conducted to determine the temperature profiles downstream of heated air jets directed at angles of 90°, 60°, 45°, and 30° to an air stream. The profiles were determined at two positions downstream of the jet as a function of jet diameter, jet density, jet velocity, free-stream density, free-stream velocity, jet total temperature, orifice flow coefficient, and jet angle. A method is presented which yields a good approximation of the temperature profile in terms of the flow and geometric conditions.

    Discussion

    INTRODUCTION

    The discharging of heated high-velocity jets of air or vapor into an air stream is employed in many …

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12. NACA-TN-2019

    "square orifices ... provided that a jet dimension equal to the diameter of the equivalent area circle was used"

    "Investigation of Flow Coefficient of Circular, Square, and Elliptical Orifices at High Pressure Ratios" ¹

    

    Abstract

    An experimental investigation was conducted to determine the penetration of air jets directed perpendicularly to an air stream. Jets issuing from circular, square, and elliptical orifices were investigated and the jet penetration at a position downstream of the orifice was determined as a function of jet density, jet velocity, air-stream density, air-stream velocity, effective jet diameter, and orifice flow coefficient. The jet penetrations were determined for nearly constant values of air-stream density at three tunnel-air velocities and for a large range of jet velocities and densities. The results were correlated in terms of dimensionless parameters and the penetrations of the various shapes were compared.

    Greater penetration was obtained with the square orifices and the elliptical orifices …

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13. NACA-TN-1615

    "it was necessary to define the penetration as the point at which the temperature is 1° F above the free-stream total temperature"

    "Investigation of the Penetration of an Air Jet Directed Perpendicularly to an Air Stream" ¹

    

    An experimental investigation was conducted to determine the penetration of a circular air jet directed perpendicularly to an air strewn as a function of jet density, jet velocity, air-stream density, air-stream velocity, jet diameter, and distance downstream from the jet. The penetration was determined for nearly constant values of air-stream density at two tunnel velocities, four jet diameters, four positions downstream of the jet, and for a large range of jet velocities and densities. An equation for the penetration was obtained in terms of the jet diameter, the distance downstream from the jet, and the ratios of jet and. air-stream velocities and densities.

    Discussion

    INTRODUCTION The introduction of a gas or vapor into …

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14. NACA-TN-1947

    "Excellent correlation was obtained between the results for a jet discharging into still air and ... into a moving air stream"

    "Investigation of Flow Coefficient of Circular, Square, and Elliptical Orifices at High Pressure Ratios" ¹

    

    Abstract

    An experimental investigation has been conducted to determine the orifice coefficient of a jet directed perpendicularly to an air stream as a function of pressure ratio and jet Reynolds number for circular, square, and elliptical orifices. The effect of air-stream velocity on the jet flow was also determined for three tunnel-air velocities. Equations for the flow coefficients In terms of jet Reynolds number and pressure ratio were obtained for the various shapes. Excellent correlation was obtained between the results for a jet discharging into still air and the results for a jet discharging into a moving air stream, provided that the correct outlet pressure was used.

    Discussion

    INTRODUCTION The introduction of a gas or …

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15. Air Jets

    "rain deflection by jet blast appears feasible for flight speeds"

    
    From NACA-RM-E55E17a.

    Introduction

    Five of these publications are from the "Jet Penetration" section, and one is from the "Windshield Ice Protection" section of The Historical Selected Bibliography of NACA-NASA Icing Publications.

    The first five publications determine by test the characteristics of air jets entering a moving airstream. The final publication applies this technology to windshield rain removal.

    Windshield rain removal is often designed in the same group as ice protection. SAE AIR-1168/4 is titled “Ice, Frost, and Rain Protection” [SAE Aerospace Applied Thermodynamics Manual, 1969 (regularly updated, currently document sae.org)]. A design group I worked in was named "Ice and Rain Protection".

    That was historically where the knowledge of water drops, air flow control, and mechanical systems resided.

    So, it is not surprising that a rain-removal publication is in the "Selected Bibliography of NACA-NASA Aircraft Icing Publications".

    Air …

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16. NACA-RM-E57G09

    "the contour plots indicate that cowl-lip disturbances are the more controlling factor"

    "Total Pressure Distortion and Recovery of Supersonic Nose Inlet with Conical Centerbody in Subsonic Icing Conditions" ¹

    

    Abstract

    Ice was formed on a full-scale unheated supersonic nose inlet in the NACA Lewis icing tunnel to determine its effect on compressor-face total-pressure distortion and recovery. Inlet angle of attack was varied from 0° to 12°, free-stream Mach number from 0.17 to 0.28, and compressor-face Mach number from 0.10 to 0.47. Icing-cloud liquid-water content was varied from 0.65 to 1.8 grams per cubic meter at free-stream static air temperatures of 15° and 0° F.

    The addition of ice to the inlet components increased total-pressure- distortion levels and decreased recovery values compared with clear-air results, the losses increasing with time in ice. The combination of glaze ice, high corrected weight flow, and high angle of …

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17. NACA-TN-4093

    "Rotational speeds up to 1200 rpm had no apparent effect on the heat-transfer characteristics of the spinner"

    "Investigation of Heat Transfer from a Stationary and Rotating Conical Forebody"

    

    Abstract

    The convective heat transfer from the surface of a conical forebody having a hemispherical nose, an included angle of approximately 30°, and a maximum diameter of 18.9 inches was investigated in a wind tunnel for both stationary and rotating operation. The range of test conditions included free-stream velocities up to 400 feet per second, rotational speeds up to 1200 rpm, and. angles of attack of 0° and 6°. Both a uniform surface temperature and a uniform heater input power density were used.

    The Nusselt-Reynold's number relations provided good correlation of the heat-transfer data for the complete operating range at 0° angle of attack with and without spinner rotation, and for 6° angle of attack with rotation. Rotational speeds up to …

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18. NACA-TN-3837

    "Many aircraft components are essentially simple bodies of revolution; examples of these are radomes, body noses, engine accessory housings, and the large spinners of turboprop engines"

    "Investigation of Heat Transfer from a Stationary and Rotating Ellipsoidal Forebody of Fineness Ratio 3" ¹

    

    Abstract

    The convective heat transfer from the surface of an ellipsoidal fore-body of fineness ratio 3 and 20-inch maximum diameter was investigated in clear air for both stationary and rotating operation over a range of conditions including air speeds up to 240 knots, rotational speeds up to 1200 rpm, and angles of attack of 0°, 3°, and 6°. The results are presented in the form of heat-transfer coefficients and the correlation of Nusselt and Reynolds numbers. Both a uniform surface temperature and a uniform input heater density distribution were used.

    The experimental results agree well with theoretical predictions for uniform surface temperature distribution. Complete agreement was not obtained …

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19. NACA-RM-E51B12

    "Serious icing of a turbojet-engine installation may render the engine inoperative in a matter of minutes."

    "NACA Investigations of Icing-Protection Systems for Turbojet-Engine Installations" ¹

    

    Abstract

    Investigations have been made in flight and in wind tunnels tc determine which components of turbojet installations are most critical in icing conditions, and to evaluate several methods of icing protection. From these studies, the requirements necessary for adequate icing protection and the consequent penalties on engine performance can be estimated.

    Because investigations have indicated that the compressor-inlet screen constitutes the greatest icing hazard and is difficult to protect, complete removal or retraction of the screen upon encountering an icing condition is recommended. In the absence of the screen, the inlet guide vanes of an axial-flow-type turbojet engine constitute the greatest danger to engine operation in an icing condition; a centrifugal- type engine, on the other hand, is relatively unsusceptible to icing once the …

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20. NACA-RM-E50H29

    "Experience has shown that ... the inlet guide vanes of an axial-flow turbojet engine constitute the most critical component to be protected from icing"

    "Investigation of Power Requirements for Ice Prevention and Cyclical De-Icing of Inlet Guide Vanes with Internal Electric Heaters" ¹

    

    Abstract

    An investigation was conducted to determine the electric power requirements necessary for ice protection of inlet guide vanes by continuous heating and by cyclical de-icing. Data are presented to show the effect of ambient-air temperature, liquid-water content, air velocity, heat-on period, and cycle times on the power requirements for these two methods of ice protection.
    The results showed that for a hypothetical engine using 28 inlet guide vanes under similar icing conditions, cyclical de-icing can provide a total power saving as high as 79 percent over that required for continuous heating. Heat-on periods in the order of 10 seconds with a cycle ratio of about 1:7 …

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21. NACA-RM-E50I08

    "Ice formations ... may have the following effects, which when combined may become serious enough to necessitate a shutdown of the engine: reduced engine thrust, increased,fuel consumption, and increased tail-pipe temperature."

    "Icing Characteristics and Anti-Icing Heat Requirements for Hollow and Internally Modified Gas-Heated Inlet Guide Vanes" ¹

    

    Abstract

    A two-dimensional inlet-guide-vane cascade was investigated to determine the effects of ice formations on the pressure losses across the guide vanes and to evaluate the heated gas flow and temperature required to prevent icing at various conditions. A gas flow of approximately 0.4 percent of the inlet-air flow was necessary for anti-icing a hollow guide-vane stage at an inlet-gas temperature of 500° F under the following icing conditions: air velocity, 280 miles per hour; water content, 0.9 gram per cubic meter; and inlet-air static temperature, 0° F. Also presented are the anti-icing gas flows required with modifications of the hollow …

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22. NACA-TN-2126

    "Use of the hot-gas method of anti-icing has been restricted ... because of difficulty in controlling the rate of heat dissipation"

    "Improvements in Heat Transfer for Anti-Icing of Gas-Heated Airfoils with Internal Fins and Partitions" ¹

    

    Abstract

    The effect of modifying the gas passage of hollow metal airfoils by the additIon of internal fins and partitions was experimentally investigated and comparisons were made among a basic unfinned airfoil section and two airfoil designs having metal fins attached at the leading edge of the internal gas passage. An analysis considering the effects of heat conduction in the airfoil metal was made to determine the internal modification effectiveness that may be obtained in gas-heated components, such as turbojet-inlet guide vanes, support struts, hollow propeller blades, arid. thin wings.

    Over a wide range of heated-gas flow and tunnel-air velocity, the increase in surface-heating rates with internal fin was marked (up to 3.5 times …

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23. NACA-RM-E8FO1a

    "The engine was satisfactorily accelerated to take-off power after approximately 45 minutes in the icing condition"

    "Natural Icing of an Axial-Flow Turbojet Engine in Flight for a Single Icing Condition" ¹

    

    Abstract

    An investigation has been conducted In natural icing conditions to determine the effect of ice formations on the performance of an axial-flow turbojet engine. One flight was made in an icing condition in which the liquid.-water content varied from 0.077 to 0.490 gram per cubic meter and the average droplet size varied from 5.4 to 12.1 microns. During a period of 60 minutes in icing, at an engine speed of 11,000 rpm, the tail-pipe temperature increased from 8650 to 9650 F and the jet thrust decreased from 1950 to 1700 pounds. Near the end of the icing period, the engine was satisfactorily accelerated to take-off power.

    Discussion

    As this publication is brief …

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24. NACA-RM-E8C18

    "Ice formations penetrated to the second-stage rotor blades"

    "Preliminary Results of Natural Icing of an Axial-Flow Turbojet Engine" ¹

    

    Abstract

    A flight investigation is being conducted. in natural icing conditions to determine the effect of ice formations on the performance of an axial-flow turbojet engine. One flight was made in icing conditions in which the icing rate varied from 5.1 to 2.1 inches per hour. During a period of 45 minutes in icing, the tail-pipe temperature increased from 761° to 1065° F and the jet thrust decreased from 1234 to 910 pounds. Ice penetrated to the second-stage stator blades. No general conclusions can be reached from these data because the icing condition was relatively light.

    Discussion

    As this publication is brief (18 pages, with 12 of those photos or blank), it is reproduced nearly in its entirety herein.

    The jet engine inlet in this case did not have …

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25. NACA-TN-1246

    "The icing of the unprotected installation presents a serious operational problem"

    "Wind-Tunnel Investigation of Icing of an Engine Cooling-Fan Installation" ¹

    

    Abstract

    An investigation was made of the icing characteristics and means of ice protection of a typIcal radial-engine cooling-fan installation, The investigation was made at various icing and performance conditions in the icing research tunnel of the NACA Cleveland laboratory.

    The icing of the unprotected cooling-fan installation was found to present a serious operational problem. Reduction in air flow below the minimum value required for engine cooling occurred within 2 minutes and complete stoppage of the cooling-air flow through the fan assembly occurred in as little as 5 minutes under normal icing conditions.

    Steam de-icing was found to be effective for the cowling lip and inlet duct. Alcohol de-icing of the fan blades and stator vanes was found to be unsatisfactory. Electrical heat de-icing of the fan blades was …

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26. Abstracts for The Historical Selected Bibliography of NACA-NASA Icing Publications

    "THIS DOCUMENT ... IS BEING RELEASED IN THE INTEREST OF MAKING AVAILABLE AS MUCH INFORMATION AS POSSIBLE"

    
    An example of the abstracts listing.

    Introduction

    The 1981 reprint of "Selected Bibliography of NACA-NASA Aircraft Icing Publications" ¹ included abstracts of the 132 references in 17 categories.

    Unfortunately, the online version available has rather poor image quality. A note is included:

    THIS DOCUMENT HAS BEEN REPRODUCED FROM
    MICROFICHE. ALTHOUGH IT IS RECOGNIZED THAT
    CERTAIN PORTIONS ARE ILLEGIBLE, IT IS BEING RELEASED
    IN THE INTEREST OF MAKING AVAILABLE AS MUCH
    INFORMATION AS POSSIBLE
    

    In some areas, the text is barely legible. I believe that this has hampered awareness about and use of this important publication.

    Here, the text is reformatted and presented here in html format, which is both human- and machine-readable.

    The formats vary in the original text. Some match what is in the publications, and others are briefer summaries typically found on …

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27. Engine Inlet Icing

    "The desirability for all-weather operation of turbojet aircraft has necessitated extensive research on methods of icing protection for the various engine components"

    
    From NACA-RM-E8C18.

    Discussion

    Publications taken largely from The Historical Selected Bibliography of NACA-NASA Icing Publications, "Turbine-Type Engine and Inlet Icing Studies" section are reviewed here.

    Reviews

    NACA-TN-1246 "Wind-Tunnel Investigation of Icing of an Engine Cooling-Fan Installation"

    • "The icing of the unprotected installation presents a serious operational problem"

    NACA-RM-E8C18 "Preliminary Results of Natural Icing of an Axial-Flow Turbojet Engine"

    • "Ice formations penetrated to the second-stage rotor blades"

    NACA-RM-E8FO1a "Natural Icing of an Axial-Flow Turbojet Engine in Flight for a Single Icing Condition"

    • "The engine was satisfactorily accelerated to take-off power after approximately 45 minutes in the icing condition"

    NACA-TN-2126 "Improvements in Heat Transfer for Anti-Icing of Gas-Heated Airfoils with Internal Fins and Partitions"

    • "Use of the hot-gas method of anti-icing has been restricted ... because of difficulty in controlling the …

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28. NACA-RM-E51L17

    "complete knowledge of the physical conditions under which supercooled clouds may exist, and the factors that cause a supercooled cloud to transform to an ice-crystal cloud is necessary"

    "A Photographic Study of Freezing of Water Droplets Falling Freely in Air" ¹

    

    Abstract

    SUMMARY

    A photographic technique for investigating water droplets of diameter less than 200 microns falling freely in air at temperatures between 0° C and -50° C has been devised and used to determine:
    (1) The shape of frozen droplets
    (2) The occurrence of collisions of partly frozen or of frozen and liquid droplets
    (3) The statistics on the freezing temperatures of individual free-falling droplets

    A considerable number of droplets were found to have a non-spherical shape after freezing because of various protuberances and frost growth, and droplet aggregates formed by collision. The observed frequency of collision of partly frozen droplets showed good order of magnitude agreement with the …

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29. NACA-TN-2532

    "supercooled water was concluded to become progressively more ice-like as the temperature is lowered"

    "X-Ray Diffraction Study of the Internal Structure of Supercooled Water" ¹

    

    SUMMARY

    A Bragg X-ray spectrometer equipped with a volume-sensitive Geiger counter and Soller slits and employing filtered molybdenum Kα, radiation was used to obtain a set of diffracted intensity curves as a function of angle for supercooled water. Diffracted intensity curves in the temperature region of 21° to -16° C were obtained. The minimum between the two main diffraction peaks deepened continuously with lowering temperature, indicating a gradual change in the internal structure of the water. No discontinuity in this trend was noted at the melting point. The internal structure of supercooled water was concluded to become progressively more ice-like as the temperature is lowered.

    Discussion

    The extensive equations included in this publication area not detailed herein.

    APPARATUS AND PROCEDURE

    A Bragg X-ray spectrometer equipped …

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30. NACA-TN-2510

    "a need has arisen for a more complete understanding of the physical properties of supercooled water because few of the physical properties of water have been investigated at temperatures much below 0° C"

    "Experimental Values of the Surface Tension of Supercooled Water" ¹

    

    Abstract

    The results of surface-tension measurements for supercooled water are presented. A total of 702 individual measurements of surface tension of triple-distilled water were made in the temperature range, 27° to -22.2° C, with 404 of these measurements at temperatures below 0° C. The increase in magnitude of surface tension with decreasing temperature, as indicated by measurements above 0° C, continues to -22.2° C. The inflection point in the surface-tension-temperature relation in the vicinity of 0° C, as indicated by the International Critical Table values for temperatures down to -8° C, is substantiated by the measurements in the temperature range, 0° to -22.2° C …

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31. NACA-TN-2234

    "very few supercooled droplets exist at temperatures lower than -35° C and the existence of an icing cloud at such low temperatures is probably an unusual occurrence."

    "Statistical Explanation of Spontaneous Freezing of Water Droplets" ¹

    

    Abstract

    A statistical theory based on the presence of small crystallization nuclei suspended in water is developed, to explain experimental results showing that on the average small droplets can be supercooled. to lower temperatures than large ones. Small nuclei of crystallization are assumed responsible for causing supercooled water to freeze spontaneously.

    The average behavior of supercooled droplets is reproduced on the basis of probability theory with an assumed distribution of crystallization nuclei with respect to the temperatures at which the nuclei cause freezing. The most probable distribution curves of spontaneous freezing temperatures for water droplets of various sizes within the size range found in clouds are obtained.

    Discussion

    In this study, data from the …

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32. NACA-TN-2142

    "Although supercooled water has been observed and reported for over two centuries, considerable disagreement exists as to the degree of supercooling possible and the factors that influence supercooling."

    "Photomicrographic Investigation of Spontaneous Freezing Temperatures of Supercooled Water Droplets" ¹

    

    Abstract

    A photomicrographic technique for investigating supercooled water droplets has been devised and used to determine the spontaneous freezing temperatures of supercooled. water droplets of the size ordinarily found. in the atmosphere. The freezing temperatures of 4527 droplets ranging from 8.75 to 1000 microns in diameter supported on a platinum surface and 571 droplets supported on copper were obtained.

    The average spontaneous freezing temperature decreased with decrease in the size of the droplets. The effect of size on the spontaneous freezing temperature was particularly marked below 60 microns. Frequency-distribution curves of the spontaneous freezing temperatures observed for droplets of a given size were obtained. Although no droplet froze at a …

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33. Properties of Water

    "Although many important advances have been made in the control of ice formation on aircraft in flight, little progress has been made toward an understanding of the fundamental processes involved in the formation of ice or the prediction of such formation."

    
    From NACA-RM-E51L17.

    Introduction

    There was limited data for properties of liquid water below the temperature of 0° C (supercooled water) at the start of the NACA-era. The five studies reviewed here sought to improve the data available.

    The authors were well-informed of other studies available at the time. New instruments were conceived and built for these studies.

    These five studies largely considered water drops, although much of the data are also applicable to more general aircraft icing analysis.

    Four of the studies concern the temperature at which supercooled water drops will spontaneously freeze (freeze without outside influence other than temperature).

    Several of the studies note similarities of the properties …

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34. Anti-Ice Heat Required Calculations with LEWICE

    
    Public domain image by Donald Cook.

    Prerequisites

    You need to have completed Anti-Ice Heat Required Calculations.

    Introduction

    Here, we will see that the values calculated by a multi-node analysis in LEWICE are comparable to the values calculated previously.

    Running LEWICE for anti-icing calculations involves (necessarily) more complex inputs. The user has to select which set of external heat transfer assumptions to use. The detailed output files require post-processing to extract the total heat required value.

    Discussion

    The LEWICE manual describes "deicer" cases that also may be used for anti-ice heat requirement analysis.
    An input is the "IDEICE" value in the case.inp file. By default, this is 0, and an unheated surface ice analysis is performed. However, with IDEICE > 0, ice protection analysis is performed, as detailed in a cased.inp file. A key input in that file is ievap, which for the cases below is set to ievap=1 …

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35. Anti-Ice Heat Required Calculations

    
    Public domain image by Donald Cook.

    Prerequisites

    You need to have completed Anti-Ice Heating Calculations Theory.

    Introduction

    For this we will use "Engineering Summary of Airframe Icing Technical Data", ADS-4, as the anti-ice examples are more detailed than those in the "Aircraft Icing Handbook", DOT/FAA/CT-88/8-1.

    The ADS-4 analysis method uses NACA-TN-2799, from 1952, for the heat and mass balance calculations. This method implements solutions as nomographs (for more details, see the post NACA-TN-2799). We will not be using the nomographs. The heat balance equations are similar to the Standard Computational Model, which we will use.

    The calculations are implemented in the file "aircraft_a_ads4.py" (and associated files) available at github.com/icinganalysis/icinganalysis.github.io. Readers are encouraged to run the analysis to the duplicate results.

    Discussion

    "Aircraft Icing", AC 20-73A, briefly mentions the terms Qa and Qr:

    Qa Heat available
    Qr Heat required

    Heat required is …

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36. Anti-Ice Heating Calculations Theory

    
    From ADS-4 apps.dtic.mil.

    Prerequisites

    You need to have completed Aircraft Icing Handbook Energy Balance Examples.

    Introduction

    We will review "Engineering Summary of Airframe Icing Technical Data", ADS-4 apps.dtic.mil, as the anti-ice examples are more detailed than those in the "Aircraft Icing Handbook", DOT/FAA/CT-88/8-1 apps.dtic.mil.

    We will also look at "Ice, Frost, and Rain Protection", SAE AIR1168/4 sae.org, for practical guidance for analysis.

    The ADS-4 and SAE AIR 1168/4 analysis methods use nomographs to implement graphical solutions. We will not be using the nomographs. While the notation is different, the analysis method from ADS-4 is very similar to the Standard Computational Model in the Aircraft Icing Handbook Merged Sections which we will use here.

    The energy balance equation is:

    Q"Source + Q"Sink = 0  
    

    Define Q"Sink by:
    

    Q"Sink = Q"conv + Q"DropWarm + Q"Evap  
    

    Define Q"Source …

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37. Using Appendix C for Ice Shape Analysis

    
    Public domain image by Donald Cook.

    Summary

    Search within the Appendix C Continuous Maximum Icing definition for the thickest ice shape.

    Prerequisites

    You need to have completed Run a 2D simulation.

    Introduction

    "Aircraft Ice Protection" AC 20-73A faa.gov offers guidance on analysis for icing conditions. We will not cover the certification aspects in detail.

    Much of the detail is on ice protection systems.

    This advisory circular (AC) tells type certificate and supplemental type certificate applicants how to comply with the ice protection requirements of Title 14 of the Code of Federal Regulations (14 CFR) parts 23, 25, 27, 29, 33, and 35.

    However, it is also useful for analysing ice shapes on unprotected surfaces.

    It is noted that:

    Determination of critical ice shape configurations is not straightforward and may require engineering judgment.

    SAE AIR5903, "Droplet Impingement and Ice Accretion Computer Codes" sae.org notes:

    A balancing of accurate and …

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38. Introduction to Variations

    
    From AC 20-73A faa.gov.

    Summary

    • Different methods (test, analysis methods) can yield different ice shapes for the same conditions
    • Measurements of ice shape parameters characterize the differences
    • What is "too large" of a difference depends on unique factors for a particular case
    • Engineering judgment is required to navigate the differences

    Discussion

    A method to characterize ice shapes

    "Aircraft Ice Protection" AC 20-73A faa.gov lists ice shape parameters that can be used to compare ice shapes:

    Applicants may use the lists of ice shape and water catch evaluation parameters in tables R-1 and R-2, ranked against their adverse airplane effects, to compare simulated and natural ice shapes. These lists are from SAE ARP5903 (Reference R20).

    Table R-1. Ranking of Ice Shape Evaluation Parameters

    Rank	Parameter	Units	Conservatism criteria
    1	Upper (suction surface) horn height		Equal or greater horn peak thickness (height)
    2	Upper Horn Angle	degree	Criticality of location …

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39. Computer Freezing Rate Analysis Tools Examples

    
    from Users Manual for the NASA Lewis Ice Accretion Prediction Code (LEWICE) (1990 version) ntrs.nasa.gov

    Prerequisites

    You need to complete the Aircraft Icing Handbook Water Catch Examples.

    You need to select a computerized tool to work with. See Analysis Toolset for obtaining LEWICE, and some other options.

    If you have chosen to use LEWICE, but you have not run it before, see the LEWICE Quick Start.

    Introduction

    We will compare energy balance terms and freezing rates calculated with the Standard Computational Model and LEWICE (or the tool that you have selected).

    The values found by differing methods are generally similar, but rarely identical.

    Aircraft Icing Handbook Example 2-4

    The mass of ice accretion on the NACA 0012 section will be calculated. Using the same flight conditions as Example 2-1. and the droplet size distribution and value from Example 2-3:

    Airfoil                         c = 3.1 foot chord NACA 0012  
    Flight …

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40. Aircraft Icing Handbook Energy Balance Examples

    
    Public domain image by Donald Cook.

    Prerequisites

    To learn the energy terms and equations, readers should first review the "Standard Computational Model", which combines the applicable sections original DOT/FAA/CT-88/8-1 and the update into one text.

    Introduction

    The term "standard computational model" has not seen wide use. Most recent literature refers to the "Messinger Model" or "Modified Messinger Model". That may or may not mean the "standard computational model" presented here. As noted for calculating evaporation:

    There are a variety of formulations of this term.

    That could also apply to several of the terms in the model. "Modified Messinger Model" could mean about anything, you would need to look at the details.

    The energy examples in the handbook are less detailed than the ones we previously saw for impingement.

    The "Standard Computational Model" is implemented here in the python programming language and is available via github.com/icinganalysis …

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41. Computer Impingement Analysis Tools Examples

    
    from Users Manual for the NASA Lewis Ice Accretion Prediction Code (LEWICE) (1990 version) ntrs.nasa.gov

    Prerequisites

    You need to complete the Aircraft Icing Handbook Water Catch Examples.

    You need to select a computerized tool to work with. See Analysis Toolset for obtaining LEWICE, and some other options.

    Aircraft Icing Handbook Example 2-2

    Example 2-2
    This example illustrates the estimation of the impingement parameters E, β, h, Su and SL using graphical data (reference 2-12). The graphical data is all presented with Ko as the independent variable. Much data is available in this form.

    The conditions of Example 2-1 for a NACA 0012 airfoil are assumed: thus Ko = 0.05. It also is assumed for simplicity that the angle of attack, α, is 0 degrees. From figure 2-11, E, the total impingement efficiency, is estimated to be 0.23 for these conditions. So about 23 percent of the water …

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42. Aircraft Icing Handbook Merged Sections

    

    Introduction

    The "Aircraft Icing Handbook" DOT/FAA/CT-88/8-1, 1991 apps.dtic.mil had a perhaps little known update in 1993: apps.dtic.mil.

    Several errors and omissions were corrected in the update, so it is essential to consult the update.

    As the update only include certain affected pages, it makes it difficult to read as there is much interruption paging back and forth between sources. Here, selected sections of the two sources are merged for easier reading.

    The reproduction quality of the online sources is variable, and parts of the update are barely legible. Here, the text is used (not just scanned images of text). In some cases, I have included text of the equations.

    Some readers may prefer the online web formatting over the pdf formatting. The figures are included inline, again to reduce paging back and forth. The cited references are also noted here. Links to online …

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43. Aircraft Icing Handbook Water Catch Examples

    
    Public domain image by Donald Cook.

    Introduction

    The "Aircraft Icing Handbook", DOT/FAA/CT-88/8-1, provides examples of two-dimensional water catch rates for the ice accretion process.

    The Handbook uses something like "US Customary" or "Engineering" units in the calculations. This may limit the direct reuse of the equations.

    These calculations can be reasonably accomplished through hand calculations, or a spreadsheet. However, they can be important "stepping stones" to build more complex capabilities.

    Code written in the python programming language is available via github.com/icinganalysis, file "intermeadiate/basics_water_catch_calculations.py" (and associated files) for the solutions, under the LGPL license. Internally, the code uses (mostly) SI units (see A Brief Digression on Unit Systems for details). There are unit conversion functions in the python code. Values here are reported in the handbook units.

    You are encouraged to run the provided code, or to start building your own library of such …

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44. LEWICE Quick Start

    
    from User's Manual for LEWICE Version 3.2 ntrs.nasa.gov

    Summary

    The "least that you need to know" to start using LEWICE, the NASA-provided icing simulation tool.

    Prerequisites

    See Analysis Toolset for how to obtain LEWICE.

    Introduction

    Decades ago there was training available for using LEWICE. I do not know of recent training. You are largely on your own, with the manual and supporting material.

    This certainly does not contain complete information, but it will help you get started in the basics of running LEWICE.

    Discussion

    The LEWICE manual provides these instructions:

    3.1.
    LEWICE Quick Start Guide
    This section is intended for users unfamiliar with LEWICE and/or DOS Shell commands. The commands below (indented bold lines) should be typed at the C:\ prompt in a DOS Shell window on a Windows machine. Alternatively, the user can use the Windows interface for any of the commands shown. Windows …

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45. Analysis Toolset

    
    Figure 15 of NACA-TN-2904 ntrs.nasa.gov.

    Summary

    You will have to choose a toolset to perform the example analyses.

    Example calculations are provided in the Python programming language, and using the NASA-provided LEWICE code.

    Introduction

    You are highly encouraged to perform the analysis described in the examples (and not just read the examples). Some examples can be accomplished with hand calculations, while other require computational capabilities.

    You need to select your toolset.

    Consider your current and future uses

    A toolset is an investment of your time and resources. By performing the calculation of the examples used here, you will build your personal and software capabilities and skills.

    Your toolset at a particular time may not be entirely your choice. Your company, institution, or customer may have policies on which kinds of software are required, encouraged, discouraged, or prohibited. Some codes have by-country use restrictions. You may have signed an …

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46. Aircraft Icing Intermediate Level

    
    From "Aircraft Icing Handbook", DOT/FAA/CT-88/8-1 apps.dtic.mil

    Summary

    After The Basics, you are ready for Intermediate level aircraft icing topics:

    • Using handbook analysis methods
    • Using computer icing analysis tools to produce ice shapes
    • Preliminary ice protection system sizing

    The Intermediate Level is a work in progress, as there may yet be many revisions and additions. However, it may be useful "as is" to some readers.

    Prerequisite: Select your toolset

    You are encouraged to run code to reproduce the examples used here. By doing so, you can build your personal and software capabilities and skills.

    Example calculations are provided here in the Python programming language, and using the NASA-provided LEWICE code.

    There are several reasons why you might use a different toolset. See Analysis Toolset for more details and options.

    Every analysis is an approximation

    We can also say that every test is an approximation:

    In these …

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47. Resources

    Introduction

    The good news is that these resources comprise thousands of pages of reading.
    The bad news is that these comprise thousands of pages of reading.

    A few experts that I know have confessed that they have not read all of what I consider to be "The Big Three", let alone everything listed here. So, you can probably get along by not reading everything.

    Most of the resources are online and available at no cost. Some are copyrighted, and available for purchase or online access rental. Your local library may be able to borrow some of them for you through inter-library loan.

    The Big Three

    These total to over 800 pages (over 1200 if one counts all three volumes of DOT/FAA/CT-88/8), but they can give you broad exposure to aircraft icing technology. However, they are now a little dated (the most recent, DOT/FAA/CT-88/8, was …

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48. Terminology

    Introduction

    These terms are taken largely from ADS-4, with updates and additions. See the Resources for other, more extensive terms lists.

    Selected Aircraft Icing Terms

    Airfoil chord: the longest line possible between the leading edge and trailing edge of an airfoil. See figure.

    Airspeed: The speed of the aircraft through the air. Sometimes measured in knots (nautical mile per hour) or KTAS. A nautical mile is about 6076 feet or 1852 m, or 1.15 statute ("standard") miles.

    Angle of attack: Angle between airfoil chord and line of flight. See figure.

    Anti-icing: The prevention of ice formation on airframe surfaces. The use of heat is the most common means of anti-icing.

    Appendix C: Appendix C of the United States Chapter 14 Code of Federal Regulations Part 25 that defines icing conditions used for certification of large transport category aircraft.

    Appendix O: Appendix O of the United States Chapter 14 Code …

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49. Ice Protection Basics

    Several areas of the airplane may require ice protection:

    
    from ADS-4 (1963)

    Forms of ice protection

    There are several forms of ice protection used on airplanes. The most commonly used for is thermal ice protection, which provides heat to the area to be protected.

    Thermal ice protection provides "Anti-Icing" protection. Anti-icing with enough heating to prevent the formation of ice by evaporating all of the impinging water is termed "Fully evaporative anti-icing". This can be a demanding amount of power for large areas.

    At lower power, "Running Wet" protection prevents ice over the heated area, but may not evaporate all of the water, which can freeze further aft of the heated area and form "Runback Ice". Analysis and test is required to show that the runback ice is acceptable.

    Runback ice on an airfoil with a heated leading edge from a laboratory test:
    
    From "Evaluation of Alternative Altitude Scaling Methods …

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50. Tools

    Aircraft designs for flight in icing are improved and proven effective by several tools, including analysis, icing wind tunnel test, and flight test in icing conditions.

    Design handbooks

    Design handbooks have charts and tables that can be used to perform analyses for aircraft icing and ice protection.

    
    from "Aircraft Icing Handbook", DOT/FAA/CT-88/8 apps.dtic.mil

    Analysis

    There are computerized icing analysis tools available from NASA, and from commercial vendors. There is also "bespoke" software created for special purposes.

    
    from "Glenn Research Center Software" www1.grc.nasa.gov

    Laboratory tests

    A wind tunnel is a large tube with a fan to produce air flow at a calibrated airspeed. Wind tunnels are used to study many effects on aircraft, including icing. Artificially produced ice shapes (often 3D printed) may be adhered to airplane models, and the effects studied.

    To simulate in-flight icing conditions, "Icing Wind Tunnels" often use refrigeration …

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51. Ice Shapes

    Types of ice shapes

    As ice accumulates on a wing, it changes the shape of the airfoil. The ice that forms is sometimes called an "Ice accretion" in the literature. The shape of the ice depends on details of the flight and icing conditions.

    At warmer temperatures (about -10°C to 0°C, depending on airspeed and other factors), ice shapes tend to produce "Glaze Ice" shapes with "horns". The nomenclature varies by domain. Pilot training materials generally note this type of ice as "Clear Ice".

    

    from "Pilot Guide: Flight in Icing Conditions", AC 91-74B faa.gov

    At colder temperatures, the ice appears milky and opaque, and is termed "Rime Ice".

    
    from "Pilot Guide: Flight in Icing Conditions", AC 91-74B faa.gov

    At temperatures in between, "Mixed Ice" can form.

    
    from "Pilot Guide: Flight in Icing Conditions", AC 91-74B faa.gov

    These types of ice can have varying effects on …

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52. Water Drops

    The size of water drops in clouds

    The water that causes most aircraft in-flight icing is small drops in clouds. Average drop sizes are typically 10 to 50 "Micrometers" (μm) in diameter (for comparison, a human hair is about 50 to 100 micrometers in diameter).

    
    Typical drop sizes, approximately proportional. Public domain image by Donald Cook.

    In a particular cloud, not all water drops are the same size. The "Langmuir Drop Size Distributions" describe an idealized approximation of how the drop sizes vary in a cloud about an average or median drop size. It has seven bins, each with a representative drop size and fraction of the total water content in the cloud.

    
    from "Aircraft Icing Handbook", DOT/FAA/CT-88/8-1 apps.dtic.mil

    The impingement of water drops on aircraft surfaces

    Calculating the amount of water that hits or impinges on the surface of an airplane as it flies …

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53. Flight

    Effects of icing in flight

    Airplanes can fly because engines produce thrust that propels it forward, and wings produce lift to counteract weight.

    A wing is a well-shaped airfoil that can produce lift with minimal drag. If ice accumulates on a wing in flight, that changes the shape of the airfoil, which is then likely to not be as efficient at producing lift. Drag can also increase.

    Effects of ice:

    Adapted from "Aviation Weather For Pilots and Flight Operations Personnel", AC 00-6A (Cancelled) faa.gov
    Public domain image by Donald Cook.

    Note that "Aviation Weather Handbook", FAA-H-8083-28 faa.gov states:

    The actual weight of ice on an airplane is insignificant when compared to the airflow disruption it causes.

    The lift an airfoil can produce is affected by the "Angle of Attack" of the wing with respect to the air motion over it.

    
    Public domain image by Donald Cook.

    The coefficient …

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54. The Basics

    "Glaze Ice" formed in flight on an airplane:
    
    from "Effects of Ice Formations on Airplane Performance in Level Cruising Flight." NACA-TN-1598, 1948. ntrs.nasa.gov

    Summary

    The Basics provide "the least that you need to know" to begin the study of Aircraft Icing.

    Introduction

    The Basics acquaint you with the specialized terminology and concepts of aircraft in-flight icing. This is intended for engineers, scientists, and administrators newly interested in aircraft icing, or for those familiar with some but not all aspects of aircraft icing.

    The Basics assume little knowledge of aircraft, and do not require math skills (there are only a few numbers that give ranges of typical values). The Basics are short and minimal, "the least that you need to know". Once you are oriented with the concepts and terms, you will be better able to ask questions and shape online searches for what you would like to know …

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55. Introducing The Basics of Aircraft Icing

    "The least that you need to know"

    
    Public domain image by Donald Cook

    Summary

    The Basics introduce core concepts and vocabulary of aircraft icing with images, "the least that you need to know".

    Discussion

    The Basics seek to facilitate initial learning about aircraft icing by:

    • focus on the needs of beginning learners
    • readily connecting to other resources for further learning
    • maximizing reuse
    • maximizing access

    Other sources may not do these well.

    Background

    One of the most-read posts that I have written was A Gentle Introduction to Aircraft Icing, so I think that there is interest in this topic.

    My learning experience

    I got a MSME degree from the University of Wisconsin Internal Combustion Engine lab. That prepared me well for some aspects of aircraft icing (heat transfer, thermodynamics, drop physics, computational fluid dynamics). However, that by itself was not enough.

    When I started in an Aircraft Systems design group, it …

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56. Conclusions of the Porter Perkins Series

    "our knowledge of aircraft icing and the penalties associated with it has not changed substantially in the last forty to fifty years" ¹

    

    From NACA-TN-1586. I believe that this is Porter Perkins, circa 1946.

    Summary

    The three areas of the many and varied contributions of Porter Perkins are reviewed.

    Discussion

    I will focus on three areas of Porter Perkins' publications:

    • Foresight about supercooled large drop (SLD) icing
    • A shift in instrument calibration
    • Contributions to the Appendix C icing regulation

    Foresight about supercooled large drop (SLD) icing

    I am not sure that I agree with the quote at the top (from 1993) now. A lot of things have happened in three decades.

    Perkins and Rieke ¹ foreshadowed in 1993 the potential effects of large-size water-drop icing conditions, now commonly termed supercooled large drop (SLD) icing:

    [Emphasis added]

    Protection from "Severe" icing encounters is not possible by definition. Likewise, there is little …

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57. Porter Perkins Flight Safety Publications

    "Most, if not all of the recent accidents on record having icing as the probable cause could have been prevented if the flight crews understood the serious nature of the situation and had applied appropriate corrective action." ²

    Summary

    Three publications on flight safety by Porter Perkins are reviewed.

    Discussion

    These publications are copyrighted. The first one, however, has a reuse license, and so much of the discussion will center on it.

    "Tailplane icing and aircraft performance degradation" 1992 ¹

    Ice on the tailplane (horizontal stabilizer) was identified as a risk on some aircraft:

    Although the sensitivity of airplanes to inflight icing has been recognized for many years and can be minimized by ice protection systems, the advent of the medium-altitude turboprop commuter transport aircraft has resulted in renewed attention to the icing problem. This review of icing has been prompted by several recent accidents that apparently were caused by …

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58. Reproducing NACA-TN-2738 Calculations

    "In view of the number and complexity of the possible sources of error, it is not possible at this time to make a reliable estimate of the total accuracy" ³

    

    Summary

    Calculations are made to assess the probability of encountering certain icing conditions.

    Introduction

    In Porter Perkins Ice Shapes and Ice Protection, references NASA TM 83564 ¹ and NASA TM 86906 ², the probability of encountering certain icing conditions was assessed, using methods from NACA-TN-2738 ³. Here, we will attempt to reproduce those calculations.

    Discussion

    In NACA-TN-2738, data were divided by geographical region.

    

    The NASA Technical Memos did not state where the natural icing test flights were. However, as three of the authors were based out of the NASA Lewis Research Center, Cleveland, Ohio, I will assume that the flights operated out of there and were in the Eastern United States region.

    So, the appropriate chart to use is Figure …

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59. Porter Perkins Ice Shapes and Ice Protection

    "An approach to characterizing the severity of an icing encounter is to relate that encounter to the frequency of its occurrence." ¹

    

    Introduction

    Three publications with Porter Perkins as an author are included here. Two publications are related, as they cover a flight test campaign to gather detailed ice shape data. The third publication describes a potential improvement to ice protection.

    There is much to see in these publications with multiple authors, and I will focus on what I believe to have been Perkins' contributions.

    Ice Shapes, NASA TM 83564 ¹ and NASA TM 86906 ²

    NASA TM 83564:

    Summary

    This paper deals with the initial results of the NASA Lewis Research Center's flight research in quantifying the performance of an aircraft in various measured icing conditions. Flight research performed in natural icing conditions supports a number of major program elements at NASA. One of these elements is to develop …

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60. Airships

    "a 2-hour flight in ... a mixture of wet snow and freezing rain ... produced no adverse effects on the operation of the airship."

    

    NACA-TN-4220, A Flight Evaluation and Analysis of the Effect of Icing Conditions on the PG-2 Airship

    Summary

    Icing threats to airships are assessed.

    Abstract

    SUMMARY

    A series of test flights was conducted by the U. S. Navy over a 3-year period to evaluate the effects of icing on the operation of the ZPG-2 airship. In supercooled. clouds, ice formed only on the forward edges of small protuberances and wires and presented no serious hazard to operation. Ice accretions of the glaze type which occurred in conditions described as freezing drizzle adversely affected various components to a somewhat greater extent. The results indicated, a need for protection of certain components such as antennas, propellers, and certain parts of the control system.

    The tests showed that icing of the large …

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61. Meteorology publications by Porter Perkins

    "Statistical values that represent the meteorological and climatic variations, which are associated with icing, will indicate what to expect in normal flight operations." ⁶

    
    From NACA-TN-4314.

    Summary

    Several publications by Porter Perkins were included in The Historical Selected Bibliography of NACA-NASA Icing Publications in the "Meteorology of Icing Clouds" section.

    Discussion

    The first several publications are only briefly described, as their major results are incorporated into the final publication, NASA Memo 1-19-59E, which will be reviewed at length.

    Note that NACA-RM-E52J06 outlines the need for data from broader sources, that is a theme in these publications:

    The majority of the research flights into icing conditions were made by attempting to select weather conditions, flight paths, and altitudes, which would yield heavy or continuous icing. Multiple traverses were often made when such conditions were found. It is impossible, therefore, to determine from this information the extent or frequency of specified icing …

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62. Propeller publications by Porter Perkins

    "As the demand for all-weather protection on aircraft for unimpaired and continuous commercial and military service developed, the detrimental effects of propeller icing on airplane performance became increasingly important"

    ¹

    
    I believe that this is Porter Perkins, circa 1946.

    Summary

    Porter Perkins investigations of propeller icing are reviewed. These are the earliest investigations by him that I found.

    Discussion

    Two areas are discussed, the gas heating of propellers, and the measurement of thrust.

    Gas heating of propellers

    • Investigation of Effectiveness of Air-Heating a Hollow Steel Propeller for Protection against Icing, I - Unpartitioned Blades. NACA-TN-1586, 1948. ¹
    • Investigation of Effectiveness of Air-Heating a Hollow Steel Propeller for Protection against Icing, II- 50-Percent Partitioned Blades. NACA-TN-1587, 1948. ²
    • Investigation of Effectiveness of Air-Heating a Hollow Steel Propeller for Protection against Icing, III - 25-Percent Partitioned Blades. NACA-TN-1588, 1948. ³

    SUMMARY

    An investigation to determine the effectiveness of icing protection afforded by air-heating hollow …

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63. Porter Perkins

    "As the demand for all-weather protection on aircraft for unimpaired and continuous commercial and military service developed, the detrimental effects of ... icing on airplane performance became increasingly important" (1948)

    

    From NACA-TN-1586. I believe that this is Porter Perkins, circa 1946.

    Summary

    Porter Perkins published on icing topics for over 50 years while at NACA, NASA, and other groups.

    Biographies and Memorials

    Porter J. Perkins is a senior aerospace engineer working in aviation safety as manager of airworthiness of research flight activity at the Lewis Research Center of the U.S. National Aeronautics and Space Administration (NASA), Cleveland, Ohio, U.S. He has specialized in research on aircraft icing for more than 25 years. His in-flight measurements to characterize icing clouds were later incorporated into U.S. icing protection certification standards. He has authored or co-authored more than 25 reports in the field of aircraft icing, and continues to participate in …

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64. Celebrating 25 Years of the NTRS

    
    The NACA Technical Reports Server, circa 1999. From NASA/TM-1999-209127. This has been superseded by the NASA Technical Reports Server ntrs.nasa.gov.

    Dust off your Netscape Navigator browser ¹ and research like it's 1999!

    Or, experience the archived version for December, 1998, at web.archive.org.

    Notes

    ---

    1. Hmm, it appears that Netscape Navigator has not been supported since 2008. Oh well, just use firefox then. ↩

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65. Conclusions of the Impingement on Surfaces thread

    "It is thus desirable to have an economical method for solving the basic water droplet trajectory equations for an arbitrary airfoil." ¹

    

    The Use of Ko for Impingement Correlations

    The use of a modified water droplet inertia parameter Ko permits consolidation into only a few graphs of most of the published water drop trajectory data. ¹

    To paraphrase NACA-TN-3839 ², the studies in this Impingement on Surfaces thread "were a rather ad hoc collection of shapes and sizes". One unifying parameter emerged to correlate the results, the "Ko" modified water drop inertia parameter.

    "Mathematical Investigation of Water Droplet Trajectories" ³

    "Mathematical Investigation of Water Droplet Trajectories" ³ defined a term Ko (see the link for definitions of other terms):

    

    Ko is not given a name, it is only defined in relation to K:

    The quantity Κ that occurs in Eqs. (4) and (5) measures the inertia of the droplet and …

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66. A Tentative Identification of Water Drop Trajectory Investigators

    NACA-TN-2094 and investigators operating the water-drop-trajectory analog

    
    Figure 15 of NACA-TN-2904

    Summary

    While no one is identified in Figure 15 of NACA-TN-2904, I speculate that these investigators are Helen M. Gallagher, and Dorothea E. Vogt. (I do not know which name goes with which individual). While neither Gallager nor Vogt is credited in NACA-TN-2904, it is possible that they contributed to the analysis, as they did in several other water-drop trajectory publications.

    Discussion

    Yes, I have used this figure a lot, as it is one of the best of the hundreds I have viewed from the NACA-era. This image is also notable in that of the hundreds of NACA-era documents that I have read, this is the only one where the people appear to be women.

    I have not been able to find photos of Gallager or Vogt for comparison (and photos of any NACA-era authors are hard to find …

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67. Impingement on Other Surfaces

    "the ideal flow field ahead of a ribbon is not a very satisfactory representation of the actual flow field in front of a rectangular body"

    

    NACA-TN-3658, "Impingement of Water Droplets on a Rectangular Half Body in a Two-Dimensional Incompressible Flow Field" ¹

    Summary

    Water-drop impingement on a rectangular body is calculated.

    Abstract

    Trajectories of water droplets moving in the ideal two-dimensional flow field ahead of a body of rectangular cross section and infinite extent in the downstream direction have, been calculated by means of a differential analyzer. Data on collection efficiency and distribution of water impingement are presented.

    Discussion

    We have already seen most of the titles on the "Impingement on Other Surfaces" topic:

    • Brun, Rinaldo J., and Mergler, Harry W.: Impingement of Water Droplets on a Cylinder in an Incompressible Flow Field and Evaluation of Rotating Multicylinder Method for Measurement of Droplet-Size Distribution, Volume-Median Droplet Size, and Liquid-Water Content …

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68. Impingement on Airfoils

    "Although the airfoils used in these studies were a rather ad hoc collection of shapes and sizes, this report makes these data generally available and correlates the data as much as possible."

    
    From NACA-TN-3839.

    NACA-TN-2931, "A Method for Determining Cloud-Droplet Impingement on Swept Wings"

    and

    NACA-TN-3839, "Experimental Droplet Impingement on Several Two-Dimensional Airfoils with Thickness Ratios of 6 to 16 Percent"

    Summary

    Several airfoils were analyzed and tested for water-drop impingement in the NACA-era.

    Abstract

    The rate and area of cloud droplet impingement on several two-dimensional swept and unswept airfoils were obtained experimentally in the NACA Lewis icing tunnel with a dye-tracer technique. Airfoil thickness ratios of 6 to 16 percent; angles of attack from 0° to 12°, and chord sizes from 13 to 96 inches were included in the study. The data were obtained at 152 knots and are extended to other conditions by dimensionless impingement parameters.
    In general …

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69. Impingement in Elbow Ducts

    "Icing of air-intake ducts and scoops with subsequent reduction in pressure recovery and in air flow may adversely affect the operation of the aircraft."

    From NACA-TN-2999. ¹

    

    NACA-TN-2999, "Impingement of Droplets in 90° Elbows with Potential Flow" ¹

    and

    NACA-TN-3770, "Impingement of Droplets in 60° Elbows with Potential Flow" ²

    Summary

    The impingement of water-drops in idealized elbow ducts is calculated with potential flow.

    Abstract

    NACA-TN-2999

    Trajectories were determined for droplets in air flowing through 90° elbows especially designed for two-dimensional potential motion with low pressure losses. The elbows were established by selecting as walls of each elbow two streamlines of the flow field produced by a complex potential function that establishes a two-dimensional flow around a 90° bend. An unlimited number of elbows with slightly different shapes can be established by selecting different pairs of streamlines as walls. The elbows produced by the complex potential function selected are suitable …

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70. Impingement in Engine Inlets

    "In spite of the simplicity, the configurations are reasonable approximation of those found on aircraft"

    NACA-TR-1317.

    
    From NACA-TR-1317.

    NACA-TR-1317, "Cloud-Droplet Ingestion in Engine Inlets with Inlet Velocity Ratios of 1.0 and 0.7."

    and

    NACA-TN-4268, "Droplet Impingement and Ingestion by Supersonic Nose Inlet in Subsonic Tunnel Conditions."

    Summary

    "Important general concepts" of impingement on engine inlets are illustrated.

    Introduction

    In the first title here, the use of potential flow to determine water-drop trajectories gets pushed to the limit. In a demonstration of the pragmatism that ran through much of the ice protection development at NACA, investigators produced results on configurations that could be analyzed that were close enough to real aircraft geometries.

    In NACA-TN-3770, we enter the supersonic jet age, with a dye-tracer method test of a supersonic inlet (but at a lower Mach number). We will see a test of "the configurations are reasonable approximation".

    Discussion

    Inlet impingement …

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71. Shadow Zones and Concentration Zones

    "... local concentration factors should be considered when choosing the location of devices that protrude into the stream from aircraft fuselages or missiles, or when determining anti-icing heat requirements for the protection of these devices."

    
    From NACA-TN-3410.

    NACA-TN-3153, "Variation of Local Liquid-Water Concentration about an Ellipsoid of Fineness Ratio 5 Moving in a Droplet Field" ¹

    and

    NACA-TN-3410, "Variation of Local Liquid-Water Concentration about an Ellipsoid of Fineness Ratio 10 Moving in a Droplet Field" ²

    Summary

    The concentration of water-drops varies with distance from a surface in flight.

    Abstract

    Trajectories of water droplets about an ellipsoid of revolution with a fineness ratio of 5 (which often approximates the shape of an aircraft fuselage or missile) were computed with the aid of a differential analyzer. Analyses of these trajectories indicate that the local concentration of liquid water at various points about an ellipsoid varies considerably and under some conditions may be …

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72. Bodies of Revolution

    "The presence of radomes and instruments that are sensitive to water films or ice formations in the nose section of all-weather aircraft and missiles necessitates a knowledge of the droplet impingement characteristics of bodies of revolution."

    ¹

    

    Summary

    Water-drop impingement on several bodies of revolution is quantified.

    Discussion

    NACA-TN-4092 ⁴ notes:

    The impingement characteristics of bodies of revolution are of interest because such bodies are representative of many aircraft components subject to icing such as radomes, body noses, engine accessory housings, and the large spinners of turboprop engines.

    NACA-TN-3099 ¹ is the first in a series and has a rather complete description of the analysis methods, so the discussion below refers to that, unless noted otherwise.

    Flow field

    Potential flow can be determined in 2D radial coordinates as well as 2D Cartesian coordinates. This was used to assess several geometries.

    The air velocity components for incompressible nonviscous flow about a …

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73. Methods of Water Drop Impingement Quantification

    "One of the first essentials ... is a method for estimating or calculating the area over which water will strike the wing, and the distribution of water impingement over that area"

    From NACA-TN-1397.

    
    From NACA-TN-3839.

    Summary

    Several methods were used to quantify the water-drop impingement on a surface, such as a wing.

    Discussion

    We already saw in the Icing on Cylinders thread calculations made for impingement on a cylinder. The technique was expanded in NACA-TN-1397 to include Joukowski type airfoils. This allowed a transformation of the flow solution around a cylinder to be mapped into airfoil coordinates, and then used to solve for water drop trajectory calculations, similar to those used for cylinders.

    NACA-TN-1397 said one could calculate "the trajectory a single drop without the utilization of a differential analyzer". We saw the differential analyzer in the Icing on Cylinders thread, in particular detail in NACA-TN-2904. However, the example given (Table …

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74. Water Drop Impingement on Surfaces

    "For a complete appraisal of the problem of ice prevention on aircraft, further water-droplet impingement data are needed" ¹

    
    Figure 5 of NACA-TN-1397

    Water Drop Impingement on Surfaces Thread

    Summary

    Water-drop impingement quantification is key to aircraft ice protection design.

    Introduction

    Part of designing for aircraft icing is determining how much ice the airplane can accumulate. For ice protection systems, determining how much water that might freeze hits a surface is a key detail.

    An important effect is that the airflow around a surface such as a wing airfoil deflects water-drops, so that all of the water-drops in the frontal area view will not hit the surface.

    Water-drop impingement quantification methods were developed to assess how many drops can hit where on a surface. Direct test methods involved the use of blotter paper to absorb water drops on a surface. Mathematical analysis of the paths individual water drops were developed …

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75. Newsletter Archive

    
    NACA Cleveland library, circa 1945.

    Summary

    Newsletters are sent to subscribers. The text is available here a few weeks after publication.

    Info about the Blast from the Past Newsletter

    Newsletters

    Links contained are not updated.

    9-30-2023
    10-9-2023
    10-16-2023
    10-23-2023
    10-30-2023
    11-06-2023
    11-13-2023
    01-08-2024
    01-15-2024

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76. The Blast from the Past Newsletter

    “The greatest of all our problems is ice.”

    "The situation changed in the mid-1920s when the intrepid aviators of the U.S. Air Mail Service attempted to maintain scheduled day-and-night operations between New York and Chicago... As one of their pilots noted at the time about the hazards of the New York-Chicago route, “the greatest of all our problems is ice.”" ¹

    
    From NACA-TN-313, 1929. ²

    Summary

    To subscribe to the newsletter: Subscribe! (via sender.net)

    Discussion

    I have an email newsletter with the latest posts and other site-related news, which you can receive regardless of the weather. Another advantage of subscribing to the newsletter is access to the secret* blog drafts that are in-work, before the public sees them, and access to the secret* newsletter archives. There is no cost to subscribe.

    [* Well, not so secret if one is acquainted with github.]

    Typical publishing sequence:

    • email newsletter, subscribers may …

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77. Site Improvements

    "I am surprised to find that there are so many details which have not been anticipated before ..."

    Reported in "Lew Rodert, Epistemological Liaison, and Thermal De-Icing at Ames". ¹

    

    Summary

    Since I started "Blast from the Past: NACA Icing Publications" 20 months ago, I have made over 100 posts. I have extensively revised some, and made improvements to all of them, so it is time to repost them.

    I will be posting links and short summaries to them in the original sequence on mastodon historians.social/@icinganalysis at a rate of three per week (about the pace that I originally posted them), so it will take almost a year to cycle through them. And I do plan on also creating new posts.

    If you want to read at you own pace, you can go to the Latest Posts tab at the top of the page for the complete list of …

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78. The NAE Proposed Meteorological Design Requirements

    "It is observed that severe icing is not predicted over large areas."

    Introduction

    This is one of the shortest post that I have written, as it is more outlining a mystery, that I have not yet sorted out, than a full review.

    Summary

    In Conclusions of the Meteorology of Icing Clouds Thread, there is a time-line of how the NACA understanding of the icing conditions evolved, focussing on liquid water content (LWC) values.

    In Canada, icing research was also being performed by the National Aeronautical Establishment (NAE).

    Here, we will compare what was published in the University of Michigan Airplane Icing Information Course, in 1953, to NACA data and the later Appendix C.

    Discussion

    Smith, E. L.: "The Design of Fluid Anti-Icing Systems" (NAE) ¹

    3.3 Meteorological Conditions

    Figure 15 presents the meteorological design requirements proposed by the Low Temperature Laboratory of the N.A.E. It is observed …

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79. Notes on Flight Testing

    "Tests to determine the performance of an icing protection system ... are of little value ... unless they can be subjected to an analytical treatment, and reduced to a generalised form which is applicable to conditions other than those under which the tests were actually made."

    Lecture No. 12b, "NOTE ON THE FLIGHT TESTING AND ASSESSMENT OF ICING PROTECTION SYSTEMS" ¹

    Summary

    An alternative view of how to correlate icing conditions to ice protection performance.

    Key Points

    1. The concepts of protection system "failure" vs. "deficiency" are discussed.
    2. Test conditions specifically planned to find the point of failure or deficiency are recommended.

    Abstract

    Flight tests of an icing protection system consist of functioning tests, tests to determine the internal efficiencies, and tests of the performance in icing. The performance in icing can be determined only if the appropriate measurements are made, and if the flow of protection or the icing severity can be …

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80. Supercooled Clouds

    "If the [ice] crystal is exceedingly small, rather than growing, it may melt."

    SUPERCOOLED CLOUDS ¹

    Summary

    Several aspect of icing clouds physics are discussed.

    Key Points

    1. Supercooling and nucleation rates are key to the formation of icing clouds.
    2. Vapor pressure differences of liquid water and ice play a role.
    3. Tips are given for recognizing supercooled clouds.
    4. Types of icing clouds are discussed.

    Discussion

    This includes a theoretical understanding of the physics of icing clouds, but also practical tips, such as how to identify supercooled icing clouds in flight.

    While this is not a long lecture (11 pages), I left out of this review for brevity items such as the artificial seeding of clouds, which is only tangentially related to aircraft icing, although I will briefly discuss that here.

    Wikipedia summarizes about the author and presenter Bernard Vonnegut:

    Bernard Vonnegut (August 29, 1914 – April 25, 1997) was an American atmospheric …

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81. University of Michigan Airplane Icing Information Course, 1953

    Thirteen lectures show the "state of the art" in 1953.

    
    See Lecture No. 6, "Energy Exchanges During Icing", Messinger, Bernard L.

    Summary

    Thirteen lectures show the "state of the art" in 1953.

    Key Points

    1. This was the best aircraft icing training and design guide available at the time.
    2. Several lectures are extracts of earlier works, or were republished later.
    3. Selected lectures are reviewed.

    Abstract

    Since there was no introduction in the bound book copy ¹ I read (it simply starts with Lecture 1). Here is a listing of the lecture titles and authors (I could not find this seemingly basic information online).

    1. "Supercooled Clouds" Vonnegut, Bernard
    2. "The Mechanics of Suspensions", Brun, Edmond
    3. "The Trajectories of Water Drops", Tribus, Myron
    4. "Heat Transfer from Streamlined Bodies", Eckert, E. R. G.
    5. "Mass Transfer at High Velocities", Mickley, Harold S.
    6. "Energy Exchanges During Icing", Messinger, Bernard L.
    7. "The Design of Air-Heated Thermal Ice-Prevention Systems …

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82. Conclusions of the Meteorology of Icing Clouds Thread

    There was remarkable progress in the three-year span 1946 through 1949.

    
    from "FLIGHT INVESTIGATION OF METEOROLOGICAL FACTORS CONDUCIVE TO AIRCRAFT ICING", William Lewis, 1947. ¹

    Summary

    The most enduring legacy of the NACA publications on icing meteorology is their direct influence on the current icing regulations.

    Key Points

    1. NACA publications contributed heavily to the creation of the Appendix C icing regulation.
    2. The key flight tests and publications were complete by 1952.
    3. Some engineering judgement went into creating the icing regulation.
    4. There was remarkable progress in the three-year span 1946 through 1949.
    5. The data from 1949 compares well to more recent flight test measurements.

    Discussion

    The most enduring legacy of the NACA publications on icing meteorology is their direct influence on the current icing regulations.

    Icing Regulations and NACA publications

    A limited understanding of atmospheric icing conditions was achieved by 1945. NACA-TN-1246 (1947) notes a "Mt. Washington Weather Bureau meeting on …

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83. NACA-TN-2738

    "A Probability Analysis of the Meteorological Factors Conducive to Aircraft Icing in the United States"

    "the probability analysis presented does provide an indication, heretofore unavailable, of the combinations of icing conditions having equal probability"

    

    Summary

    The icing design values in NACA-TN-1855 were found to have an exceedance probability Pe=0.001.

    Key Points

    1. A rigorous probability analysis of the considerable icing flight test data was conducted.
    2. The icing design values in NACA-TN-1855 were found to have an exceedance probability Pe=0.001.

    Abstract

    Meteorological icing data obtained in flight in the United States are analyzed statistically and methods are developed for the determination of:

    (1) the various simultaneous combinations of the three basic icing parameters (liquid-water content, drop diameter, and temperature) which would have equal probability of being exceeded in flight in any random icing encounter; and

    (2) the probability of exceeding any specified group of values of liquid-water content …

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84. NACA-TN-2569

    "A Summary of Meteorological Conditions Associated with Aircraft Icing and a Proposed Method of Selecting Design Criterions for Ice-Protection Equipment" ¹

    "the heat required for protection for this [severest] situation is several times that required for the most probable icing condition."

    

    Summary

    By allowing some ice to accumulate in severe icing conditions, the peak energy requirements for ice protection can be reduced.

    Key Points

    1. The altitude and temperature boundaries for Continuous Maximum Icing are establish that are later used in Appendix C.
    2. "A total of 305 traverses of cumuliform clouds by P-61C airplanes were made in icing conditions, and on no occasion did ice accumulate before the end of a traverse to such an extent as to make safe flight impossible."
    3. "the heat required for protection for this [severest] situation is several times that required for the most probable icing condition."
    4. "Ice-protection equipment for some critical aircraft components, such as …

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85. NACA-TN-2306

    "the collection of data indicating the maximum extent, severity, and frequency of conditions"

    "Meteorological Analysis of Icing Conditions Encountered in Low-Altitude Stratiform Clouds"

    

    Summary

    Data about the horizontal and vertical extend of icing clouds.

    Key Points

    1. A factor of distance traveled in icing related to liquid water content is noted.
    2. The maximum vertical extent of icing clouds is quantified.
    3. "Observations ... during the 1948-49 and 1949-50 winters were in substantial agreement with values previously reported."

    Abstract

    Liquid-water content, droplet size, and temperature data measured during 22 flights in predominantly stratiform clouds through the 1948-49 and the 1949-50 winters are presented. Several icing encounters were of greater severity than those previously measured over the same geographical area, but were within the limits of similar measurements obtained over different terrain within the United States. An analysis of meteorological conditions existing during the 74 flights conducted for four winters indicated an inverse relation of …

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86. NACA-TN-1855

    "Recommended Values of Meteorological Factors to be Considered in the Design of Aircraft Ice-Prevention Equipment" ¹

    "Progress ... has been handicapped by the lack of sufficient data on the meteorological factors."

    

    Summary

    Icing conditions for the design of equipment are proposed, which are later part of Appendix C.

    Key Points

    1. Classes of icing conditions are proposed.
    2. Recommendations are made by type of equipment as to which class apply.
    3. This became the basis for a large part of the later CFR 14 Part 25 Appendix C.

    Abstract

    Meteorological conditions conducive to aircraft icing are arranged in four classifications: three are associated with cloud structure and the fourth with freezing rain. The range of possible meteorological factors for each classification is discussed and specific values recommended for consideration in the design of ice-prevention equipment for aircraft are selected and tabulated. The values selected are based upon a study of the available observational data …

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87. NACA-TN-1793

    "Complete information concerning the fundamental physical processes that determine the structure of clouds and cloud systems has necessitated a statistical approach to the problem."

    

    "Investigation of Meteorological Conditions Associated with Aircraft Icing in Layer-Type Clouds for 1947-48 Winter"

    Summary

    Measured icing conditions in 1947-48 were consistent with prior measurements.

    Key Points

    1. Measured icing conditions in 1947-48 were consistent with prior measurements.
    2. Cumulative-frequency graphs of indicate the frequency of various icing conditions.
    3. The Weather Bureau scale of icing intensity is used as a comparison to measured data.

    Abstract

    SUMMARY
    Rotating-cylinder measurements of the icing conditions encountered in flight during the winter of 1947-48 are presented. Liquid-water content, drop size, and temperature data are shown to be consistent with previously measured conditions and with proposed maximum icing conditions in supercooled layer-type clouds. Cumulative-frequency graphs of meteorological parameters indicate the frequency with which various icing conditions have been encountered in the Great Lakes …

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88. NACA-TN-1391

    "liquid water concentration at any point in the cloud may be calculated by considering an air parcel lifted adiabatically from the condensation level"

    "Icing Properties of Noncyclonic Winter Stratus Clouds"

    Summary

    Adiabatic lift theory is used to estimate the liquid water content of clouds.

    Key Points

    1. Adiabatic lift theory is used to estimate the liquid water content of clouds.
    2. Drop size instrumentation was limited to a 4 inch cylinder for maximum drop size.
    3. "Calculations ... show that the liquid water concentration in noncyclonic stratus clouds is not likely to exceed 1.5 grams per cubic meter."

    Abstract

    Introduction
    In order to establish a rational basis for the efficient design of thermal ice-prevention systems for airplanes the Ames Aeronautical Laboratory of the National Advisory Committee for Aeronautics has undertaken experimental investigation of the meteorological conditions conducive to the formation of ice on aircraft. A C-46 airplane has been equipped to measure free-water …

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89. Meteorology of Icing Clouds

    "The maximum icing conditions in which ice-prevention equipment will be expected to provide adequate protection"

    
    from "FLIGHT INVESTIGATION OF METEOROLOGICAL FACTORS CONDUCIVE TO AIRCRAFT ICING", William Lewis, NACA Conference on Aircraft Ice Prevention A Compilation of Papers Presented by NACA Staff Members. 6505/NACA-1947/8, 1947.

    Summary

    Early Ice Protection Systems were designed without detailed knowledge of icing conditions in clouds. While successful designs were accomplished with extensive iteration and flight test, more optimal design is only possible if the conditions are known beforehand.

    Discussion

    Progress ... has been handicapped by the lack of sufficient data on the meteorological factors.
    NACA-TN-1855, 1949.

    A better understanding of the icing atmosphere evolved in parallel with improved Meteorological Instruments in the years 1944 to 1952. Two of the authors (Kline, Lewis) were meteorologists from the US Weather Bureau. This helped put the data on a sound scientific basis.

    Reviews in this thread:

    • Meteorology of …

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90. Ideas for future posts

    "... Before attacking what appeared to be a new icing problem we should study the icing work of the 1940's and 50's." ¹

    
    From NACA-TN-2904

    Summary

    I have made this blog up as I went along. I have a general plan to cover all 132 icing publications in the "Selected Bibilography of NACA-NASA Aircraft Icing Publications", but I also find other interesting, related items along the way.

    Future topic possibilities include:

    • Water drop impingement (there are 20 publications in the "Selected Bibilography of NACA-NASA Aircraft Icing Publications" that I have not yet gotten to).

    • The University of Michigan 1953 Airplane Icing Information Course. A "Greatest Thing That You (Probably) Have Never Read" candidate.

    • Accomplished! Thread: The University of Michigan Airplane Icing Information Course, 1953

    • NACA Conference on Aircraft Ice Prevention A Compilation of Papers Presented by NACA Staff Members. 6505/NACA-1947/8, 1947.
      This is available at DTIC.

    • Project Cirrus, Final …

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91. Conclusions of the Ice Protection Thread

    "The industry has now passed through the experimental stages of heating and anti-icing ..." (1946) ¹

    From NACA-ACR-A-53, 1941.

    Summary

    Ice protection system development continues to address new challenges.

    Key Points

    1. Design guides can lead you to "adequate" designs for several technologies.
    2. Design guides provide procedures to compare candidate systems.
    3. Optimal designs and new requirements may require system development.

    Discussion

    We have seen "the possible methods for overcoming the ice hazard" that were developed in the NACA-era in this Ice Protection Thread. The period up to and through WWII (1945) was largely characterized by expeditious tests to address immediate icing problems.

    The quote above "The industry has now passed through the experimental stages of heating and anti-icing ..." from 1946 was not completely the case, but NACA did move on to more planned scientific and engineering tests and analysis methods development. By the 1950's useful Engineering Design Manuals were available, so that …

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92. Design Manuals

    "An aircraft engineer can use this report to design adequate ice protection systems for any type aircraft for any flight mission profile." ¹

    
    Figure 4.2-2 of ADS-4.

    Summary

    The knowledge of aircraft icing matured to produce engineering design manuals.

    Key Points

    1. NACA publications contributed heavily to later design manuals.
    2. Extensive design publications distilling research into practical methods appeared in the 1950s.
    3. I do not know of a comprehensive design resource for some recent topics such as 3D design and analysis.

    Discussion

    NACA had an early period (up to and including WWII) that was largely characterized by expeditious tests to address immediate icing problems. Later, NACA embarked on more scientifically oriented studies. The science and experience of aircraft ice protection had matured enough by the 1950s for comprehensive engineering design manuals to be written.

    While NACA did not write all of the design manuals, all of the design manuals heavily …

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93. Instructive Illustrations

    

    Summary

    While icing weather is a serious topic for aircraft, several sources have used [debatably] humorous, instructive illustrations of the hazards.

    Discussion

    Aviation Weather For Pilots and Flight Operations Personnel. AC 00-6A (Cancelled) ¹

    

    See also The Greatest Thing That You Have (Probably) Never Read: AC 00-6A (Cancelled)

    "Mechanical De-Icing Systems" ²

    

    See also University of Michigan Airplane Icing Information Course, 1953.

    Air Command Weather Manual (Canada) ³

    

    Icing Hazards - National Weather Service ⁴

    

    NASA - Introduction to Aircraft Icing ⁵

    

    Notes

    ---

    1. Anon.: Aviation Weather For Pilots and Flight Operations Personnel. AC 00-6A (Cancelled), FAA, issued April, 1975, cancelled 2016. faa.gov ↩

    2. Loughborough, D. L.:"Mechanical De-Icing Systems", (B. F. Goodrich Company), Lecture No. 10, University of Michigan Airplane Icing Information Course, 1953. ↩

    3. Anon., Air Command Weather Manual (Canada), CFACM 2-70, May 22, 2001. ↩

    4. weather.gov ↩

    5. Von Hardenberg, Paul: Introduction to Aircraft Icing and NASA’s Approach to Understanding It. March …

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94. Thermal Analysis and Surface Wettedness

    "ice formation can be redefined in more general terms as a thermodynamic problem" ¹ (1936)

    Summary

    The thermal analysis of icing conditions has unique challenges, including the determination of heat transfer coefficients and fraction of the surface wetted.

    Key Points

    1. Measured heat transfer coefficients in dry air can be different between flight and tunnel tests, due to free stream turbulence.
    2. Icing conditions tend to promote more turbulent flow on the surface.
    3. Assumptions about the fraction of the surface wetted aft of impingement affect the thermal analysis.

    Introduction

    Experience indicates that certain types of control surfaces, for example, accumulate ice, while others do not. It suggests the need for particular care in the design of slotted controls, the more especially as de-icers can hardly be used in a slot. While of course much of this work can only be done in a refrigerated tunnel where practical tests of actual ice deposit …

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95. Component Icing

    "I am surprised to find that there are so many details which have not been anticipated before the de-icing tests were started." (1942)

    
    Figure 1 from NACA-TN-1789.

    Summary

    The effects of icing on small components must be addressed.

    Key points

    1. Flight tests in natural icing revealed (and still reveal) small component icing effects.
    2. Fuel vents designs were evaluated.
    3. "At present very little is known of the effect of radome icing on radar operation."
    4. The effect of icing on the radome for radar was evaluated.

    Introduction

    We saw some details of the Lewis Rodert's work on the Lockheed 12A test aircraft in Engine Exhaust Heat. However, wing ice protection was not the only challenge:

    To fly into ice clouds and survive, the Ames group necessarily became expert on the impact of ice on the total aircraft. "I am surprised to find", noted [NACA Langley] Engineer-in-Chief Smith DeFrance, "that there are so …

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96. Windshield Ice Protection

    "... ice on the airplane windshield, which is known to be a problem in urgent need of solution."

    
    Figure 14 from NACA-TN-1434.

    Summary

    Ice protection for windshields matured during the NACA-era.

    Key points

    1. In 1939: "The existing practice of making the airplane windshield retractable or removable by the pilot ... against loss of vision due to rain or ice"
    2. By 1947, window heat designs similar to current designs were available.

    Discussion

    Ice protection for windshields matured during the NACA-era.
    Technology progressed from this in 1939 (NACA-SR-130):

    The existing practice of making the airplane windshield retractable or removable by the pilot ... against loss of vision due to rain or ice

    By 1947, there were electrical window heating ice protection designs similar to current designs (NACA-TN-1434).

    "An Investigation of the Prevention of Ice on the Airplane Windshield", NACA-SR-130 ¹ and NACA-TN-754 ²

    INTRODUCTION
    The National Advisory Committee for Aeronautics is conducting a program of …

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97. Freezing Point Depressant Fluids

    "Alcohol as a means of protection against ice formation on propeller blades is widely used by commercial air lines on transport airplanes." ¹

    
    Figure 2 from NACA-RB-4F06.

    Summary

    Freezing point depressant fluids were used widely in the NACA-era.

    Key points

    1. The use of freezing point depressant fluids were not pioneered by NACA, NACA studied improvements.
    2. Analysis methods were developed in the NACA-era.
    3. Freezing point depressant fluids are still used today.

    Discussion

    This is a technology that was not invented by NACA. NACA studies sought to improve the use of freezing point depressant fluids.

    When mixed with water, a freezing point depressant fluids lowers the freezing/melting temperature of the mixture, and enough fluid can lower that temperature below the equilibrium wet surface temperature, preventing or removing ice.

    There are many potential freezing point depressant fluids. In the NACA-era, alcohols were the most widely used. Today, for aircraft deicing on the …

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98. Combustion heated air and heat transfer coefficients

    "an effective system for ... wing surfaces to prevent the formation of ice requires knowledge"

    
    Figure 2 of NACA-ARR-A506

    Summary

    Combustion heated air, independent of the engines, was used on some aircraft.

    Key Points

    1. Combustion heaters were developed independently of NACA.
    2. 38 NACA publications detail technical aspects of aircraft heaters, including many details on heat exchangers, maturing engineering designs.
    3. Three publications deal with heat transfer for ice protection.

    Discussion

    There were numerous NACA publications on aircraft heaters. For the combustion heaters, air was scooped in, heated by burning aviation gasoline, and used for cabin heating, and wing ice protection on some airplanes (The DC-6, for example).

    Combustion heaters were developed independently of NACA prior to these NACA publications. However, the NACA publications very much detailed the design of not just the heaters, but also associated heat exchangers and components, as well as data needed for analysis (such as "An Investigation of …

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99. Electrothermal Ice Protection

    "... the power required for ice prevention may be excessive for certain applications, although sufficient power for some degree of ice removal may be provided readily." ¹

    
    Figure 12 of NACA-ARR-4A20.

    Summary

    Electrothermal deicing is studied in the NACA-era.

    Key Points

    1. The power levels required for continuous anti-ice are challenging, so deicing was persued.
    2. Runback ice and residual ice are challenges for deicing.
    3. Analogue computers calculated transient heating and deicing.
    4. A chordwise-sequenced zone heating ice shedding strategy was devised.
    5. The current 787 jet aircraft uses electrothermal heating for wing anti-icing and de-icing.

    Discussion

    The electric powered deicing of propeller blades, as well as wing leading edges, was studied by NACA.

    The deicing of propellers is perhaps easier in some ways, as the centrifugal of the spin greatly aids the shedding of ice. Also, there are scale differences, as a wing airfoil usually has a larger chord length than a propeller. However …

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100. Compressed Air Heat

     "the most economical icing protection ... consists of a system utilizing hot gas from a convenient heat source, namely, the turbojet-engine compressor" ¹

     
     From NACA-TN-2866.

     Summary

     Compressed air heating becomes common for ice protection in the jet era.

     Key points

     1. To support jet engine powered transportation, NACA had several studies of ice protection using compressed air heating.
     2. Deicing schemes were proposed to reduce the amount of air bled from the engines.
     3. Some innovative features, like continuously heated parting strips and recirculating hot air supply, did not see much use.
     4. Compressed air heating is used widely today for jet powered transports.

     Discussion

     As aviation entered the jet propulsion age, reciprocating-engine exhaust heat was not an option. However, the jet engine air compressor offers an ample (but not unlimited) supply of hot, compressed air that may be bled from the engine compressor airstream for ice protection, cabin heating, and other functions.

     Several NACA …

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101. Engine Exhaust Heat

     "an airplane that will be immune from the dangers of ice accumulation ... is only a matter of technical development." ¹

     

     Summary

     Practical wing heating designs are developed and proven in natural icing flight tests.

     Key Points

     1. Flight tests were used extensively, as icing wind tunnels were still under development.
     2. Much detailed development over 10 years was required.
     3. "Existing data indicate that sufficient heat is available... the problem is one of distribution".
     4. Design elements were developed that could be used in future compressed air heating.

     Discussion

     NACA-TR-403 ¹

     This investigation was conducted by the National Advisory Committee for Aeronautics to study the practicability of employing heat as a means of preventing the formation of ice on airplane wings. The report relates essentially to technical problems regarding the extraction of heat from the exhaust gases and it proper distribution over the exposed surfaces. In this connection a separate study has been made …

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102. Carburetor and Induction Systems

     "A demon was operating the throttle." S. W. Sparrow, 1920. ¹

     
     From NACA-TR-982.

     Summary

     Carburetor icing has been a known hazard for over 100 years, and many protection strategies were studied in the NACA-era.

     Key Points

     1. Carburetor icing has been a known hazard for over 100 years.
     2. Part of the hazard can occur in clear air (throttling icing and fuel-evaporation icing).
     3. "The NACA induction-system icing program at the National Bureau of Standards was initiated in January 1941. The project is financed jointly by the Army, the Navy, and the National Advisory Committee for Aeronautics."
     4. Numerous tests and studies were conducted in the NACA-era.
     5. Many aircraft today have carburetor protection similar to that developed in the NACA-era.

     Discussion

     The spark ignition, Otto cycle engines commonly used on airplanes in the NACA-era typically had carburetors to control the air and fuel entering the cylinders for combustion. These could be affect by ice …

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103. Deicing boots and ice adhesion

     "The removal of ice from a De-Icer surface depends on the true adhesion of ice to rubber..." ⁴

     
     Image from “Engineering Summary of Airframe Icing Technical Data” ADS-4, 1963.

     Summary

     Pneumatic boot deicers were the first widely used form of aircraft ice protection, and are still used today.

     Key Points

     1. Deicing boots were developed independent of NACA.
     2. Oil coatings aid the shedding of ice.
     3. NACA development efforts largely shifted to thermal deicing in the 1940s.

     Introduction

     As detailed in "We Freeze to Please": A History of NASA's Icing Research Tunnel and the Quest for Flight Safety, the “expanding rubber sheet” or “ice-removing overshoe” for ice protection was developed independently of NACA in the 1930s, and was the first widely used method of aircraft ice protection. Small passages within the rubber could be periodically inflated to shed ice (typically once every two minutes). While some "inter-cycle" ice forms, the maximum amount …

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104. Hard to find publications

     "The documents were so old, however, that they were not listed in the modern computerized library search systems, and some of these documents were out of print." ¹

     
     NACA Cleveland library, circa 1945.

     Summary

     I can usually get even rare and obscure publications through inter-library loan from my public library, but these were reported as having no loanable copies available.

     Discussion

     I have tried the many excellent search tips at Gwern's Internet Search Tips, and now I am at the "request help" stage.

     I would appreciate any help anyone can offer finding them as loanable print copies or digitally.

     Recently made available

     • Heat Transfer Calculation for Aerofoils RAE Rep. No. Aero. 1783, Nov. 1942. Reprinted as NACA MRR No. 3E29, May 1943.
       I requested it through airsciences.org.uk and they sent me a scanned pdf copy (not sharable, so you will have to request your own copy).

     Could only …

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105. Ice Protection

     "The possible methods for overcoming the ice hazard ..." ¹

     
     From NACA-ACR-A-53, 1941. ²

     Summary

     Numerous methods were tested to find effective aircraft ice protection in the NACA-era.

     Introduction

     During the war, more than a hundred cargo planes of the Air Transport Command, flying from bases in India over the Hump to battlefronts in China, crashed in the Himalayas. Most of them were brought down by ice. In a single day in 1944, nine of these big Army transports, loaded with sorely needed supplies for the Allies’ fighting forces, were lost.
     Many of the fatal crashes of commercial aviation have been traced to this same cause. For years commercial transports have been equipped with anti-icing devices, but the apparatus in common use was designed to assist in meeting an emergency when it arises, not to prepare the plane for deliberate flight into ice clouds. If dangerous icing conditions are inadvertently encountered …

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106. Out-Sourcing My Work to ChatGPT and DALL-E

     "ChatGPT may produce inaccurate information about people, places, or facts"

     From https://chat.openai.com/ ChatGPT August 3 Version (2023).

     

     Summary

     The image was generated with DALL-E 2 with the prompt "An airplane from 1946 flying with engine exhaust heat ice protection". I have no idea what the orange thing (ribbon and bow?) is on the wing.

     I also tried letting ChatGPT write a blog post.

     Prompt: "Write a blog post about the use of engine exhaust heat for aircraft ice protection during the era of the National Advisory Committee for Aerodynamics, including citations"

     Response:

     The National Advisory Committee for Aerodynamics (NACA) was a organization in the United States that existed from 1915 to 1958. During its existence, NACA carried out research on various aspects of aerodynamics, including the use of engine exhaust heat for aircraft ice protection.

     One of the early NACA reports on this topic, "Investigation of the …

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107. One Year Review

     "... Before attacking what appeared to be a new icing problem we should study the icing work of the 1940's and 50's." ¹

     One year of "Blast from the Past: NACA Icing Publications"

     

     Image from "NACA Conference on Aircraft Ice Prevention A Compilation of Papers Presented by NACA Staff Members" 6505/NACA-1947/8, 1947. (colorized) (and the new logo for 2023)

     I made 50+ posts in the past 12 months.

     I am thankful for the continuing level of interest shown in the topic.

     Progress on the 132 NACA Icing Publications

     I set out to review the 132 publications in the "Selected Bibilography of NACA-NASA Aircraft Icing Publications".

     Out of 132 publications, I wrote 33 reviews.
     (links to the individual reviews are included in the "Selected Bibilography of NACA-NASA Aircraft Icing Publications")

     There is still a long way to go!

     Some areas have had more coverage than others:

     • Meteorology …

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108. Conclusions of the Meteorological Instruments Thread

     "difficulties with the calibration proved to be more serious than had been anticipated" ¹

     

     Summary

     The meteorological instruments and data from the NACA-era are still used today.

     Key Points

     1. The rotating multicylinder was the primary instrument that determine the values in the current Appendix C icing regulations.
     2. Other instruments gave supplementary data, but were calibrated against the rotating multicylinder.
     3. Later publications document the continuing use of the NACA-era instruments.

     Discussion

     NACA-era instruments

     In this Meteorological Instruments thread we saw several instruments and technologies:

     • Rotating Multicylinders
     • Fixed Cylinder
     • Rotating-Disk Icing-Rate Meter
     • Capillary Collector
     • Rainbow Recorder
     • Dew-Point Recorder
     • Visibility Meter
     • Sooted Slides (and oiled slides)
     • Drop Photography
     • Heated probes
     • Inference from drop impingement
     • Modified pressure probe
     • Corona discharge (multicylinder)

     Instruments used to derive icing requirements

     The instruments and flight data from the NACA-era were used to develop the current "Appendix C" icing certification standard ².

     

     ³

     [As we saw in "Conclusions of …

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109. NACA-RM-E51E16

     "A measure of the concentration of liquid water in a supercooled cloud is of considerable value in determining the severity of aircraft icing conditions"

     "A Simplified Instrument for Recording and Indicating Frequency and Intensity of Icing Conditions Encountered in Flight"

     ¹

     Summary

     An instrument for automatically recording the occurrence of icing and liquid water content values is described.

     Key Points

     1. The instrument relied on the plugging of holes exposed to icing, which made a measurable pressure difference.
     2. The instrument was cyclically deiced with electric heating.
     3. Data was recorded on film that was later processed.
     4. The instrument was used on numerous flights.

     Abstract

     An instrument for recording and indicating the frequency and intensity of aircraft icing conditions has been developed by the NACA Lewis laboratory to obtain statistical icing data over world-wide air routes during routine airline operations. An accumulation of data of this type is needed to provide pertinent meteorological …

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110. NACA-TN-2458

     "Because the charge placed on the droplets is a function of the droplet size, the size spectrum can be determined ..." ¹

     "An Instrument Employing a Coronal Discharge for the Determination of Droplet-Size Distribution in Clouds"

     Summary

     Electrical charges imparted to water drops allowed easier measurement of impingement on cylinders.

     Key Points

     1. This was a multicylinder instrument that relied on the differential collection efficiency of different cylinder sizes.
     2. The measurement of electrical charge allowed easier measurement of impingement rates.
     3. There does not appear to be further use or development of the instrument.

     Abstract

     A flight instrument that uses electric means for measuring the droplet-size distribution in above-freezing clouds has been devised and given preliminary evaluation in flight. An electric charge is placed on the droplets and they are separated aerodynamically according to their mass. Because the charge placed on the droplets is a function of the droplet size, the size spectrum …

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111. The Greatest Thing That You Have (Probably) Never Read: 1969 Aircraft Ice Protection Report of Symposium

     "The subject of aircraft ice protection has provoked much controversy and discourse among theorists, designers, laboratory and test engineers, and flight operations people." ¹

     

     Summary

     The state of the art in 1969 of aircraft icing is documented in 16 presentations.

     Abstract

     The subject of aircraft ice protection has provoked much controversy and discourse among theorists, designers, laboratory and test engineers, and flight operations people. In view of this diversity of opinion and variety of approach, some difficulty has been experienced in applying current standards and in maintaining uniformity in the substantiation of aircraft ice protection. This symposium recognized the need to exchange ideas and it provided a general review of icing criteria, ice protection standards, methods of compliance, and service experience. It also served as a general refresher for Federal Aviation Administration personnel involved in the evaluation of aircraft ice protection. Technical papers were presented by government research and test …

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112. Mastodon

     

     "Blast from the Past: NACA Icing Publications" now posts on the Mastodon social network.

     You do not need an account to view the posts, they are available at historians.social/@icinganalysis.

     If you have an ActivityPub or "fediverse" social media account, you can follow @[email protected].

     At the moment, the posts are "old" ones (aren't they all?), but they will eventually (over several weeks) catch up to the current posts.

     I do plan to continue posting on LinkedIn. Mastodon may well reach a different audience.

     You can learn more about Mastodon at docs.joinmastodon.org.

     Note: an earlier edit of this post had a different address for Mastodon. I have since changed instances. The community on historians.social is a better fit for this than a general use instance. Switching instances is a normal thing in the fediverse.

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113. airfoil impingement drop distribution

     "... it is believed that a comparison of the water-drop impingement over several different airfoils ... is of interest"

     
     Figure 5 from NACA-TN-1397

     NACA-TN-1397, "A Method for Numerically Calculating the Area and Distribution of Water Impingement on the Leading Edge of an Airfoil in a Cloud." ¹

     NACA-TN-2476, "An Empirical Method Permitting Rapid Determination of the Area, Rate, and Distribution of Water-Drop Impingement on an Airfoil of Arbitrary Section at Subsonic Speeds." ²

     NACA-RM-E52B12, "Impingement of Water Droplets on an NACA 651-212 Airfoil at an Angle of Attack of 4°." ³

     Summary

     Three publications detail water impingement calculations.

     Key Points

     1. Impingement analysis methods are detailed.
     2. Data for several airfoils are presented.
     3. Methods to estimate impingement without the use of a differential analyzer are included.
     4. An instrument is not described, but the later NACA-TN-3338 does describe drop size distribution measurements.

     Abstract

     NACA-RM-E52B12 ³

     The trajectories of droplets in the air flowing past an …

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114. Heated Probes

     "a simple and rapid means for measuring the liquid-water content of clouds" ¹

     NACA-RM-E50J12a, "Flight Instrument for Measurement of Liquid-Water Content in Clouds at Temperatures Above and Below Freezing"

     NACA-TN-2615, "The Calculated and Measured Performance Characteristics of a Heated-Wire Liquid-Water-Content Meter for Measuring Icing Severity"

     NACA-RM-A54I23, "A Heated-Wire Liquid-Water-Content Instrument and Results of Initial Flight Tests in Icing Conditions"

     We will detail NACA-RM-A54I23 herein, as that was the final in the series of publications detailing the development, and will include some detail from the earlier NACA-RM-E50J12a and NACA-TN-2615.

     Summary

     Electrically heated probes can measure water exposure rate, from which LWC can be calculated.

     Key points

     1. The technology evolved over the span of the three publications.
     2. A heated wire probe can provide measurements with low lag (~1 second), faster than other technologies available in the NACA-era.
     3. There was an earlier "cloud indicator" based on similar technology.
     4. The technology is still used …

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115. Water Drop Imaging

     "it is necessary to measure the sizes of the droplets within the clouds." ¹

     NACA-RM-E50K01a, "Flight Camera for Photographing Cloud Droplets in Natural Suspension in the Atmosphere"

     NACA-RM-E51G05, "Adaptation of a Cascade Impactor to Flight Measurement of Droplet Size in Clouds"

     NACA-TN-3592, "An Oil-Stream Photomicrographic Aeroscope for Obtaining Cloud Liquid-Water Content and Droplet Size Distribution in Flight"

     Summary

     Three strategies were explored for water drop imaging.
     In NACA-RM-E50K01a, a telephoto arrangement allowed imaging water drops in situ.
     In NACA-RM-E51G05, water drops were put through a particle size sorting cascade, impacting on slides, and imaged.
     In NACA-TN-3592, water drops were captured in an oil stream exposed to the ambient flow, and then imaged.

     Key Points

     1. Three methods for obtaining images of water drops are discussed.
     2. Images of enough water drops allowed the calculation of the drop size distribution.
     3. These instruments had limited influence in the NACA-era.

     Abstract

     NACA-RM-E50K01a:

     A camera designed …

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116. NACA-RM-A9C09 Instruments

     "This [rotating disk] device should prove very useful in both the formative and statistical investigations."

     "A Review of Instruments Developed for the Measurement of the Meteorological Factors Conducive to Aircraft Icing" ¹

     
     from NACA-RM-E51E16 ²

     Summary

     "A review ... of meteorological factors conducive to aircraft icing reveals outstanding needs" for icing instrumentation.

     Key points

     1. Nine instruments, based on differing technologies, are qualitatively assessed.
     2. "The [multicylinder] method has assumed the position of a standard against which other instruments are calibrated, and is apt to remain so..."
     3. "This [rotating disk] device should prove very useful in both the formative and statistical investigations."
     4. "A reliable method for the measurement of drop-size distribution should be developed"

     Abstract

     The status of instrument suitable for the measurement of the meteorological factors conducive to aircraft icing is reviewed. The meteorological factors to be evaluated are listed, and tentative values for the desired and acceptable accuracy of measurement for …

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117. A Gentle Introduction to Aircraft Icing

     "Icing is as close to pure witchcraft engineering as you can get."

     Thomas S. on LinkedIn.

     Figure 13 of NACA-TN-1598. Formation of ice from flight on horizontal stabilizer. Average icing rate, 4 inches per hour; liquid-water content, 0.4 grams per cubic meter; drop size, 17 microns. (Painted stripes are 1 inch wide, indicating an ice thickness of about 2 inches.)

     Summary

     This website was written with people in mind (engineers, aerodynamicists) who already know something about aircraft and aircraft icing.

     To make it a little more understandable to others, I summarize here the assumed common knowledge, with a few of the key technical terms.

     Discussion

     Airplanes require lift from the wings in order to fly. This lift is produced due to details of the air flowing over the well-shaped wing.

     Ice may form on airplanes in flight in certain weather conditions. The ice changes the shape of the wing …

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118. Meteorological Instruments

     "A review ... of meteorological factors conducive to aircraft icing reveals outstanding needs"

     Meteorological Instruments Thread

     

     Summary

     Several instruments were developed and improved during the NACA-era to measure icing conditions.

     Numerous modes of physics were explored, and distant descendants of some devices are still used today.

     See also Icing on cylinders, and Calibration of the NACA Icing Wind Tunnels.

     Reviews

     Rotating Multicylinders

     • NACA-TN-2708, Comparison of Three Multicylinder Icing Meters and Critique of Multicylinder Method.
     • NACA-RM-E53D23, Procedure for Measuring Liquid-Water Content and Droplet Sizes in Super-cooled Clouds by Rotating Multicylinder Method.

     Nine instruments NACA-RM-A9C09

     • Rotating Multicylinders
     • Fixed Cylinder
     • Rotating-Disk Icing-Rate Meter
     • Capillary Collector
     • Rainbow Recorder
     • Dew-Point Recorder
     • Visibility Meter
     • Sooted Slides
     • Drop Photography

     Water drop imaging

     • NACA-RM-E50K01a
     • NACA-RM-E51G05
     • NACA-TN-3592

     Heated probes

     • NACA-RM-E50J12a
     • NACA-TN-2615
     • NACA-RM-A54I23

     Inference from airfoil impingement

     • NACA-TN-1397
     • NACA-TN-2476
     • NACA-RM-E52B12

     Corona discharge

     • NACA-TN-2458

     Modified pressure probe

     • NACA-RM-E51E16

     Conclusions of NACA Icing Instruments

     Possible additions

     • Vonnegut, B., Cunningham, R. M., and Katz …

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119. Large Drop Icing Conditions in Icing Wind Tunnels

     "effects are scaled appropriately between Appendix C and SLD conditions using the existing scaling methods"

     

     Summary

     Icing wind tunnel uses and challenges for large drop icing are discussed.

     Key points

     1. Since 2014, supercooled large drop (SLD) icing has been part of (US) 14 CFR Part 25 icing regulations (Appendix O).
     2. Physics make current icing wind tunnels challenged to reproduce the freezing rain portion of Appendix O.
     3. For the "main" leading edge region ice shape, the standard test similarity calculations apply.
     4. Icing extent limits appear to have unexplained variability in test.
     5. Ice protection test similarity has not been addressed in detail for SLD conditions.

     A Very Brief Description of Supercooled Large Drop (SLD) Icing Conditions

     I will keep this brief and focused on icing wind tunnels.

     For a more complete description of SLD icing, see Hu ¹. While Appendix O ² is only 10 page long, AC 25-28 ³ describing acceptable …

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120. AIAA-2017-3927

     "With a thermal IPS, energy reduction can be achieved by operating in a ‘running wet’ mode under more extreme icing conditions."

     

     "Evaluation of Alternative Altitude Scaling Methods for Thermal Ice Protection System in NASA Icing Research Tunnel" ¹

     Summary

     A procedure for scaling conditions for ice protection tests is detailed.

     Key Points

     1. Scaling methods for ice protection testing at sea level conditions were evaluated.
     2. The "WePi3" scaling method was recommended.
     3. The method requires in-test adjustments of heating to match reference surface temperatures.
     4. Test conditions for unheated areas will be different from those for heated areas.

     Abstract

     A test was conducted at NASA Icing Research Tunnel to evaluate altitude scaling methods for thermal ice protection system. Two new scaling methods based on Weber number were compared against a method based on Reynolds number. The results generally agreed with the previous set of tests conducted in NRCC Altitude Icing Wind Tunnel where …

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121. The Effects of Humidity in Icing Wind Tunnel Tests

     "a condition of supersaturation, which promotes the growth of frost deposits"

     Summary

     Supersaturated humidity can affect icing wind tunnel results.

     Key Points

     1. Some observations of supersaturated humidity conditions were made in the NACA-era.
     2. Supersaturation was associated with frost on test article afterbodies.
     3. Recirculating icing wind tunnel conditions are calculated to tend to be supersaturated.
     4. Some potential effects of supersaturation are calculated.

     A brief primer on humidity

     A measurement of water vapor in the air is humidity. Relative humidity is the most common measure. In everyday life 30% to 60% relative humidity is generally considered to be comfortable. Lower humidities feel dry, and higher humidities feel wet or "humid".

     The most water vapor that can usually exist at a given static temperature is termed "saturated", and that condition has 100% relative humidity. Given sufficient time and condensation surfaces, any surplus vapor above this value will condense as liquid water.

     Natural icing …

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122. Manual of Scaling Methods

     "... it was not surprising that scale ice shapes were again a good match for the reference"

     NASA/CR-2004-212875 ¹

     

     Summary

     Similarity calculations for ice shapes are detailed.

     Key Points

     1. Several scaling methods with differing parameters are compared in tests.
     2. "The Ruff method, supplemented with the constant-We_L approach to calculate scale velocity, is recommended"
     3. Examples are included of how to deal with limitations (temperature, lwc, etc.)

     Abstract

     This manual reviews the derivation of the similitude relationships believed to be important to ice accretion and examines ice-accretion data to evaluate their importance. Both size scaling and test-condition scaling methods employing the resulting similarity parameters are described, and experimental icing tests performed to evaluate scaling methods are reviewed with results. The material included applies primarily to unprotected, unswept geometries, but some discussion of how to approach other situations is included as well. The studies given here and scaling methods considered are applicable …

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123. Bilanin Pi Terms and the Weber Number

     "An unfortunate fact is that if proposed additional scaling parameters prove to be what is required to conduct improved subscale tests, icing wind tunnel subscale tests are likely to be even more restrictive."

     "Proposed Modifications to Ice Accretion/Icing Scaling Theory" ¹

     Summary

     Water surface tension is identified as a factor in ice shapes and test similarity.

     Key points

     1. 18 dimensionless Pi-terms were identified.
     2. "the π method has failed to provide a scaling methodology which can be used to test subscale aerodynamic components"
     3. "however, does not preclude seeking approximate scaling methodologies"
     4. Several later studies investigate the role of water surface tension and the Weber number.

     Abstract

     The difficulty of conducting full-scale icing tests has long been appreciated. Testing in an icing wind tunnel has been undertaken for decades. While aircraft size and speed have increased, tunnel facilities have not, thus making subscale geometric tests a necessity. Scaling laws governing these …

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124. AEDC-TR-87-23

     "drag coefficient (Cd) was used as an index of similitude by quantitatively indicating how much the shape or ice surface changed"

     

     "An Empirical Look at Tolerances in Setting Icing Test Conditions with Particular Application to Icing Similitude" ¹

     Summary

     An investigation into which icing conditions parameters affect icing similtiude as measured by aerodynamic drag effects.

     Abstract

     Often, engine icing tests cannot be conducted at conditions that are considered the critical test points because of aircraft engine test facility operational constraints or the inability to find the desired conditions in natural icing flight tests. The use of ice scaling laws may circumvent this testing limitation. Earlier studies (Refs. 1 and 2) of the application of ice scaling (similitude) to aircraft engine testing indicated that experimental data were needed to determine to what extent icing test conditions [temperature (T), velocity (V), liquid water content (LWC), median volume diameter (MVD), pressure (P)], could …

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125. AEDC-TR-85-30

     "It would be beneficial to the icing community if the feasibility of using scale models in these tests could be proven."

     

     "Analysis and Verification of the Icing Scaling Equations" ¹

     Summary

     An expanded set of icing similarity terms are derived and tested.

     Key Points

     1. Water drop impingement similarity is simplified using Ko.
     2. Icing heat transfer similarity terms derived from Messinger are added.
     3. Tests in an icing wind tunnel validate the selected set of similarity terms.

     Abstract

     1.1 BACKGROUND

     The formation of ice on aircraft surfaces occurs during flight through supercooled droplets. Ice accretions on these surfaces usually degrade both aircraft performance and operational safety. For this reason, it has become important in the design and certification phases of system development to evaluate system performance degradation because of icing.

     The most acceptable method of evaluating the performance characteristics of aircraft and aircraft components for system certification would be to conduct …

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126. Scaling in NACA Icing Wind Tunnel Tests

     "If the values of the K and φ parameters for the model and full-scale nacelle are maintained the same, the icing characteristics of the model will be similar to the icing characteristics of the full-scale"

     Summary

     Early examples of icing test scaling are noted.

     Key Points

     1. Three publication that mention scaling are reviewed.
     2. Some challenges with scaling are noted.
     3. A airfoil design of a full scale leading edge truncated with an aft flap addresses some challenges.

     Discussion

     NACA-RM-E8A27 "Ice Protection of Turbojet Engines by Inertia Separation of Water, I - Alternate-Duct System" ¹

     This is the earliest example that I have found of using dimensionless water drop impingement terms for test similarity calculations.

     The results of a preliminary investigation of internal water- inertia separation inlets designed to prevent automatically the entrance of large quantities of water into a turbojet engine in icing conditions are presented. A simplified analytical approach to the …

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127. Calibration of the NACA Icing Wind Tunnels

     "Considerable time [was devoted] to means for controlling the amount of water sprayed into the air stream, the size of water particles, and the temperatures of the air and water" ¹

     Summary

     Calibration methods evolved during the NACA-era

     Key Points

     1. Early tests had informal calibrations, partly due to a limited understanding of the natural icing environment.
     2. Rotating multicylinders were the most used means of calibration.
     3. Water spray nozzles were improved circa 1949.
     4. The understanding of the natural icing environment had also advanced by 1949.

     Discussion

     As implied from the quote above from the year 1929, the calibration of an icing wind tunnel is often not just measuring what the facility produces, but also altering and improving the facility to achieve target values for water drop size and liquid water content, and producing a water drop spray that is uniform "enough".

     Early calibrations

     Two early icing wind tunnel tests had informal …

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128. Site Navigation and Suggested Reading Order

     "There is no order in the world around us, we must adapt ourselves to the requirements of chaos instead."

     Attributed to Kurt Vonnegut. For some more information about Kurt and his brother Bernard, see Supercooled Clouds.

     
     NACA Cleveland library, circa 1945.

     Summary

     There are over 100 articles on this website. Here is a guide to get to what you are interested in.

     NACA-era icing publication reviews *

     (* Well, mostly, a few post-NACA era ones are mixed in.)

     This is the main focus of the blog, the National Advisory Committee for Aeronautics publications on aircraft icing, 1915 to 1958.

     There are 132 publications in The Historical Selected Bibliography of NACA-NASA Icing Publications . (Not all of them have been reviewed yet.)

     This blog was written in "threads" or themes on topics. Threads will have links to several articles. It is suggested, but not required, to read the articles in the order below.

     • Introduction …

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129. Uses of NACA-Era Icing Wind Tunnels

     "Icing wind tunnels can simulate natural icing with water-spray and refrigeration systems ... to permit safe, convenient and relatively inexpensive testing." ¹

     
     How much of a P-39 can one fit into an icing wind tunnel?

     Summary

     A wide variety of test articles were used in the NACA-era Icing Research Tunnel (IRT)

     Key Points

     1. 37 publications were found describing the use of the IRT.
     2. A wide variety of test articles were used in the NACA-era Icing Research Tunnel

     Discussion

     Readers are encouraged to see "We Freeze to Please": A History of NASA's Icing Research Tunnel and the Quest for Flight Safety, which includes information from NACA-era internal memos and interviews that I have not seen published elsewhere.

     There were five icing wind tunnels used by NACA. The majority of the tests were performed in the Icing Research Tunnel (IRT) as NACA Lewis. The four other tunnels are briefly described in the "Other …

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130. NACA-TN-339

     "A spray, which consisted of very small drops, was found to be quite satisfactory"

     "Refrigerated Wind Tunnel Tests on Surface Coatings for Preventing Ice Formation"

     Summary

     An early icing wind tunnel and test are described

     Key Points

     1. An early icing wind tunnel with most of the components of current tunnels is described.
     2. A test of several coatings to prevent ice is detailed.
     3. Many of the points noted about icing tunnel test reflect current test experience.

     Abstract

     This investigation was conducted in the Refrigerated Wind Tunnel at Langley Memorial Aeronautical Laboratory, Langley Field, Virginia, to determine the effectiveness of various surface coatings as a means for preventing ice formations on aircraft in flight. The substances used as coatings for these tests are divided into two groups: compounds soluble in water, and those which are insoluble in water. It was found that certain soluble compounds were apparently effective in preventing the formation …

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131. Icing Wind Tunnel Test Thread

     
     from NACA-TN-1246

     "Icing wind tunnels can simulate natural icing with water-spray and refrigeration systems ... to permit safe, convenient and relatively inexpensive testing." ¹

     Summary

     While there were extensive publications on how to use aerodynamic wind tunnels in the NACA-era (for example, Pope's "Wind Tunnel Testing" ²), there was no reference for using icing wind tunnels that I could find, and I cannot think of a current publication that provides comprehensive guidance (there are publications that cover specific aspects, as we shall see in the thread).

     This thread will not by itself correct that problem, but it will summarize uses, and perhaps provide some guidance by examples.

     As there are numerous NACA publications (40+) that describe specific icing wind tunnel tests, but only a little about the icing wind tunnel itself in each one, I will not have a detailed review of most of the individual publications in this thread. Instead …

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132. Conclusions of the Ice Shapes and Their Effects Thread

     "an irregular shape is developed due to the ice formation, which is ruinous to the aerodynamic efficiency of the airfoils" ¹

     

     from NACA-TN-1598 ²

     Summary

     Data from the post-NACA era are used to resolve open questions

     Key Points

     1. The Ice Shapes and Their Effects thread is summarized.
     2. Post-NACA era data is used to resolve some open questions.
     3. Correlations of drag due to ice have limited, "first order" accuracy.

     Discussion

     Review of the "Ice Shapes and Their Effects" thread so far

     In this thread, we saw:

     An almost "lost gem" of the NACA-era, NACA-TN-313, "The Formation of Ice upon Airplanes in Flight" with, in 1929: - Description of supercooled large drop (SLD) icing conditions
     - "Detect and exit" icing mitigation strategy
     - Natural icing flight tests of icephobic materials
     - Identification of different types of icing

     The effect of "protuberances" on an airfoil section lift and drag in NACA-TR-446, "Airfoil Section Characteristics as Affected by …

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133. Six Month Review of Blast from the Past: NACA Icing Publications

     "You can't connect the dots looking forward; you can only connect them looking backwards."

     Attributed to Steve Jobs.

     
     One of the earliest icing wind tunnel tests on surface coatings to prevent ice, NACA-TN-339, 1929. Sometimes, there is a learning curve.

     Summary

     I have been posting for about six months now, so it is time to review how it is going.

     I thank all of my readers. I want to write things that are read, and you make this worthwhile.

     I started out with the statement "I make selected NACA publications easily accessible to you". By some measures, I have been achieving that, and I welcome your opinions of how well I am doing.

     Discussion

     Things that work

     Interest in the topic

     I presented "NACA Publications on Aircraft Icing: Cylinders" to the SAE AC-9C Aircraft Icing Technology Committee and it was well received.

     A measure of interest is views of a …

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134. The Greatest Thing That You Have (Probably) Never Read: 1969 Aircraft Ice Protection Report of Symposium, Ramon Wilder

     "The upper surface [ice] horn acts as a spoiler, increasing drag, and reducing lift."

     

     "Techniques Used to Determine Artificial Ice Shapes and Ice Shedding, Characteristics of Unprotected Airfoil Surfaces" ¹

     Summary

     Glaze ice shape correlations for two commercial aircraft airfoils are developed.

     Key Points

     1. Icing wind tunnel tests with two commercial aircraft airfoils were conducted.
     2. Glaze ice shape correlations were developed.
     3. Airplane level ice effects are detailed.
     4. The state of the art in 1969 is documented.

     A Note

     I briefly worked with Ramon Wilder (circa 1991?), but I did not ask him about this particular publication. I (a much junior engineer) asked him off-handedly about a certain heat conduction equation. He said "I'll get back to you." The next day he came in with an elegant, hand-written, 10 page proof, and said "That was a little tough. It took me three hours last night!" That was the kind of engineer …

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135. NASA-TM-D-2166

     "this correlation is a first-order approximation of the presently available aerodynamic and icing data for airfoils exposed to icing conditions"

     SAE Preprint No. 225, "Correlation of Airfoil Ice Formations and Their Aerodynamic Effects With Impingement and Flight Conditions"

     and

     NASA-TM-D-2166, "Prediction of Aerodynamic Penalties Caused by Ice Formations on Various Airfoils"

     The content of these two publications are almost identical. As NASA-TM-D-2166 is the one that was cited the most, and has a more legible copy available online, I will center the review around it.

     Summary

     A more general correlation of drag due to ice on an airfoil is developed.

     Key Points

     1. Several airfoils are studied in addition to the NACA 65A004 previously used.
     2. A more general correlation of drag due to ice on an airfoil is developed.
     3. For lift, "no systematic relation is readily apparent for a thin, sharp-nosed airfoil such as the 65A004 airfoil".

     Abstract

     An empirical equation …

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136. NACA-TN-4151

     "published aerodynamic data for performance penalties in icing conditions are not readily applicable to a very thin airfoil"

     NACA-TN-4151, "Correlations Among Ice Measurements, Impingement Rates, Icing Conditions and Drag Coefficients for an Unswept NACA 65A004 Airfoil"

     and

     NACA-TN-4155, "Aerodynamic Effects Caused by Icing of an Unswept NACA 65A004 Airfoil"

     These two publications reference each other, and so are reviewed together.

     Summary

     Correlations are develop between ice shapes, aerodynamic performance, and icing conditions.

     Key Points

     1. More than 60 ice shapes were measured in an icing wind tunnel for a thin airfoil section.
     2. Correlations were developed between ice shapes, aerodynamic performance, and icing conditions.

     Abstract

     NACA-TN-4155:

     The effects of ice formations on the section lift, drag, and pitching-moment coefficients of an unswept NACA 65A004 airfoil section of 6-foot chord were studied. The magnitude of the aerodynamic penalties was primarily a function of the shape and size of the ice formation near the …

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137. NACA-RM-E53J30

     "It is desirable to evaluate the effect of sweepback on the shape of the leading-edge ice formations and the associated drag penalties"

     "Effect of Ice Formations on Section Drag of Swept NACA 63A-009 Airfoil with Partial-Span Leading-Edge Slat for Various Modes of Thermal Ice Protection" ¹

     Summary

     The section drag due to ice on a swept airfoil section is measured.

     Key Points

     1. "At low rates of water catch, the rate of drag increase for the unheated swept 63A-009 airfoil is approximately 2 1/2 times as great as that of the unswept airfoil of reference 1 for similar icing conditions"
     2. "In general, the studies showed that icing on a thin swept airfoil will result in more detrimental aerodynamic characteristics than on a thick unswept airfoil."
     3. "small amounts of runback icing on the upper surface easily induced flow separation"

     Abstract

     The effects of primary and runback ice formations on the section …

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138. NACA-TN-2962

     "The results showed that glaze-ice formations, either primary or runback, ... caused large and rapid increases in drag, especially at datum air temperatures approaching 32F"

     NACA-TN-2962, "Effect of Ice and Frost Formations on Drag of NACA 65₁-212 Airfoil for Various Modes of Thermal Ice Protection" ¹

     

     Summary

     The drag due to ice shapes (including runback) are measured over a range of conditions.

     Key Points

     1. "The results showed that glaze-ice formations, either primary or runback, ... caused large and rapid increases in drag, especially at datum air temperatures approaching 32F"
     2. There is an early statement of icing wind tunnel test to flight similarity.
     3. Different phases of flight (takeoff, cruise, descent), including sequences, are considered.
     4. By "discriminating use of the data", drag results can be estimated using NACA-TR-446.

     Abstract

     The effects of primary and runback icing and frost formations on the drag of an 8-foot-chord NACA 651-212 airfoil section were investigated over …

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139. NACA-TN-1598

     "It is significant that the control response of the airplane approached the point of being marginal when all of the airplane except the propeller had accreted ice"

     

     NACA-TN-1598, "Effects of Ice Formations on Airplane Performance in Level Cruising Flight" ¹

     Summary

     Airplane levels effects of icing are measured, and broken into major components.

     Key Points

     1. Numerous, excellent quality photos show how icing flight test "should be done".
     2. Airplane levels effects of icing are measured, and broken into major components.
     3. "It is significant that the control response of the airplane approached the point of being marginal when all of the airplane except the propeller had accreted ice."

     Abstract

     A flight investigation in natural icing conditions was conducted by the NACA to determine the effect of ice accretion on airplane performance.

     The maximum loss in propeller efficiency encountered due to ice formation on the propeller blades was 19 percent. During 87 percent …

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140. NACA-WR-L-292

     "The danger lies, not so much in the higher stalling speed, but more in the possibility that the stall may occur without advance warning to the pilot."

     NACA-WR-L-292, "Effects of a Simulated Ice Formation on the Aerodynamic Characteristics of an Airfoil" ¹

     Summary

     Airfoil characteristics with simulated residual ice are measured.

     Key Points

     1. An airline operator survey of ice shapes was conducted.
     2. A residual ice shape was tested at near full scale.
     3. A significant reduction in Cl_max values was found.
     4. Values are compared to NACA-TR-446.

     Abstract

     In connection with the general study of icing problems an item of major interest is the effect of ice on the aerodynamic characteristics of a wing. Of particular interest is the effect of the ice which remains on a wing, under some flight conditions in spite of the operation of rubber de-icers. At the request of the N.A.C.A. a questionnaire seeking …

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141. NACA-TR-446

     "As regards the lift at higher angles of attack ..., the [effect] becomes increasingly serious as the protuberance approaches a point near the leading edge."

     

     NACA-TR-446, "Airfoil Section Characteristics as Affected by Protuberances" ¹

     Summary

     "Protuberances" on an airfoil can have significant effects on section lift and drag.

     Key Points

     1. Position and height of the protuberance are important.
     2. While icing is not mentioned, later works will apply this data in an icing context.

     Abstract

     The drag and interference caused by protuberance from the surface of an airfoil have been determined in the N.A.C.A. Variable-Density Wind Tunnel at a Reynolds Number of approximately 3,100,000. The effects of variations of the fore-and-aft position, height, and shape of the protuberance were measured by determining how the airfoil section characteristics were affected by the addition of th various protuberances extending along the entire span of the airfoil. The results provide …

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142. NACA-TN-313

     "an irregular shape is developed due to the ice formation, which is ruinous to the aerodynamic efficiency of the airfoils"

     NACA-TN-313, "The Formation of Ice upon Airplanes in Flight" ¹

     

     Summary

     Ice shapes are recorded in flight tests in natural icing conditions.

     Key Points

     1. Types of ice formations are noted, clear ice (possibly SLD) and rime ice.
     2. The atmospheric conditions for the types of ice are noted.
     3. "Oily surface" icephobic substances are tested.
     4. Procedures for avoiding the most hazardous icing conditions are provided.

     Abstract

     This report describes the atmospheric conditions under which ice is deposited upon the exposed parts of airplanes in flight. It identifies the formation which is found under different conditions, and describes some studies of preventative means together with recommendations for avoiding the consequences of the formation.

     Discussion

     This is an almost "lost gem" of the NACA-era (cited only 10 times).
     It features:
     - Description of supercooled large …

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143. Ice Shapes and Their Effects

     "an irregular shape is developed due to the ice formation, which is ruinous to the aerodynamic efficiency of the airfoils" ¹

     

     from NACA-TN-1598 ²

     Ice Shapes and Their Effects Thread

     Summary

     This thread will cover ice shapes and the aerodynamic effects of the ice.

     This will primarily cover ice shapes on unprotected surfaces.

     There are additional publications on ice shapes for deicing systems and propellers that will not be reviewed here.

     Publications

     NACA-TN-313, "The Formation of Ice upon Airplanes in Flight"

     Ice shapes are recorded in flight tests in natural icing conditions.

     NACA-TR-446, "Airfoil Section Characteristics as Affected by Protuberances"

     "Protuberances" on an airfoil can have significant effects on section lift and drag.

     NACA-WR-L-292, "Effects of a Simulated Ice Formation on the Aerodynamic Characteristics of an Airfoil"

     Airfoil characteristics with simulated residual ice are measured.

     NACA-TN-1598, "Effects of Ice Formations on Airplane Performance in Level Cruising Flight"

     Airplane levels effects …

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144. NACA-TN-3024-revisited

     "evaporation losses are ... very small (less than 1 percent) in the case of smaller obstacles (of icing-rate-measurement-cylinder size)."

     "Maximum Evaporation Rates of Water Droplets Approaching Obstacles the Atmosphere under Icing Conditions" Evaporation calculations ¹

     

     Summary

     Less that 1% of drops evaporate approaching an obstacle for most cases.

     Key points

     1. Equations are detailed for the evaporation of water drops approaching an obstacle.
     2. The equations were coded into a python program.
     3. Less that 1% of drops evaporate approaching an obstacle for most cases.
     4. A water drop that approaches on the stagnation line but does not impinge is predicted to evaporate away.

     NACA-TN-3024 was reviewed previously, herein we will concentrate on comparing our own code to the results in NACA-TN-3024.

     Abstract

     When a closed body or a duct envelope moves through the atmosphere, air pressure and temperature rises occur ahead of the body or, under ram conditions, within the duct. If cloud water …

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145. AEDC1DMP

     "The third part of the study comprised some numerical computations of two-phase, dilute, air and entrained water particle flows, using a new version of the AEDC one-dimensional, multiphase flow code, AEDC1DMP."

     

     The AEDC 1-Dimensional Multi-Phase code (AEDC1DMP) and the iads1dmp

     Abstract

     The AEDC1DMP calculates the water drop speed and evaporation in an icing wind tunnel. The AEDC1DMP is described in "Second Report for Research and Modeling of Water Particles in Adverse Weather Simulation Facilities" ¹. AEDC is the Arnold Engineering Development Complex, formerly the Arnold Engineering Development Center.

     1.0 INTRODUCTION TO THE RESEARCH
     This report describes a continuation of research into the modeling of water particle freezing for application to adverse weather simulation facilities. The research was initiated in FY1996 to investigate the physics of freezing of submillimeter supercooled water particles or droplets in both natural and artificial or simulated adverse weather environments. The first phase of the research …

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146. Let's Build a 1D Water Drop Trajectory Simulation

     

     "The discrepancies are of the magnitude to be expected from ... the step by step integration". ¹

     Let's build a 1D water drop trajectory simulation

     Summary

     Water impingement values on a cylinder are calculated with step-by-step integration.

     Key points

     1. 1D equations of motion were implemented.
     2. Results agree well with the minimum drop size required for impingement.
     3. Water drops may contact the cylinder at very low K values.
     4. The methods appears accurate enough to use for other applications.

     Discussion

     We are going to start with a one dimensional simulation along a single line, the stagnation line of flow around a cylinder, y=0 in the figure above.

     We will implement the equations of motions for a drop around a cylinder from "Mathematical Investigation of Water Droplet Trajectories" ¹.

     Readers unfamiliar with "Mathematical Investigation of Water Droplet Trajectories" may wish to review it before proceeding further herein, especially to be familiar with the …

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147. Super-Cooled Water Droplets in Rising Currents of Cold Saturated Air

     "It is possible to develop this theory to cover also growth of water droplets during the adiabatic expansion of a rising mass of saturated air."

     

     Irving Langmuir, "Super-Cooled Water Droplets in Rising Currents of Cold Saturated Air"

     Summary

     Evaporation and condensation rates on water drops are calculated.

     Key Points

     1. A theory of water drop growth by condensation in the atmosphere is developed.
     2. The drop size measurement by oiled-slide and multicylinder instruments is improved.
     3. The evaporation rates of stationary water drops is analyzed.

     Abstract

     As this is an extensive work (130 pages), and as Langmuir did not provide an abstract or introductory summary, we will begin with the Langmuir's conclusions as a summary.

     Summary of Main Conclusions of Part I to April 1, 1944

     Before analyzing the new data it is desirable to summarize the main conclusions reached from the foregoing parts of this report:

     1. The Glauert theory of the deposition …

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148. Water drop evaporation

     "snow-flakes will form and these will grow by vapor condensation and by evaporation of fog droplets" ¹

     

     A "mini-thread" on the evaporation of water drops

     Summary

     This thread will have a mix of NACA-era and post-NACA era data on water drop evaporation.

     Topics:

     Irving Langmuir, "Super-Cooled Water Droplets in Rising Currents of Cold Saturated Air"

     Evaporation and condensation rates on water drops are calculated.

     Let's build a 1D particle motion simulation: Impingement on the stagnation point of a cylinder

     A 1D water drop motion simulation is built.

     The AEDC 1-Dimensional Multi-Phase code (AEDC1DMP) and the iads1dmp

     Water drop evaporation rates in an icing tunnel are calculated.

     NACA-TN-3024 revisited

     Less that 1% of drops evaporate approaching an obstacle for most cases.

     Related

     The next thread in the NACA review series is the Icing Wind Tunnel Test Thread.

     Notes

     ---

     1. Langmuir, Irving: Super-Cooled Water Droplets in Rising Currents of Cold Saturated Air, Pt …

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149. Conclusions of the Icing Thermodynamics Thread

     "The collection of ice by the cylinders is similar to the collection of ice by airplane components"

     

     Figure 1. Modes of energy transfer for an unheated airfoil in icing conditions.

     Conclusions of the Icing Thermodynamics Thread

     Summary

     Data from the post-NACA era are used to resolve open questions

     Key points

     1. The Icing Thermodynamics thread is summarized.
     2. Post-NACA era data is used to resolve some open questions.
     3. The "Messinger model" and extended Messinger models are prevalent in current icing analysis.

     Discussion

     Review of the Icing Thermodynamics thread so far

     In the Icing Thermodynamics thread, we saw:

     • Calculations of wet surface temperatures NACA-ARR-5G13
     • Two dimensional heated surface equations for ice protection NACA-TR-8311
     • Comparisons of natural icing flight data to 2D ice protection calculations NACA-TN-1472
     • The "Ludlam limit" for freezing all water impinging Ludlam, F. H.: The Heat Economy of a Rimed Cylinder
     • The term "freezing fraction" defined Messinger, B. L.: Equilibrium Temperature …

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150. ADS-4

     "these calculations, performed at several span stations, can become unnecessarily tedious"

     ADS-4, “Engineering Summary of Airframe Icing Technical Data” ¹

     

     Summary

     A single thermodynamic control volume is used for anti-ice calculations.

     Key points

     1. Ice shapes are classified (glaze, rime).
     2. A single thermodynamic control volume is used for anti-ice calculations.
     3. NACA icing publications are extensively used.

     Abstract

     This report provides, in a single reference document, an engineering summary of selected technical data on airframe icing conditions, methods of detecting, preventing, and removing ice from airframes in flight, and methods of testing ice protection systems to ensure their adequacy. An aircraft engineer can use this report to design adequate ice protection systems for any type aircraft for any flight mission profile.
     The work done in preparing this report covered a survey, study, analysis, and summary of the vast amount of technical literature on airframe icing available in the world today. Key technical …

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151. NACA-TN-3396

     "into the transonic and supersonic regimes, the frictional heating becomes of considerable importance to icing."

     "Icing Limit and Wet-Surface Temperature Variation for Two Airfoil Shapes under Simulated High-Speed Flight Conditions"

     ¹

     

     Summary

     Predictions of the icing limit temperature were "sufficiently accurate" in tests at Mach 1.35.

     Key points

     1. Surface temperatures in icing conditions are challenging to measure.
     2. Apparently small differences in pressure coefficient and recovery factor values are important at high Mach values.
     3. Partial surface wettedness makes comparisons between analysis and test challenging.
     4. Thermal conduction in the substrate affects runback ice.
     5. Predictions of the icing limit temperature were "sufficiently accurate" in tests at Mach 1.35.

     Abstract

     Frictional heating resulting from flight at high speeds effectively reduces the value of ambient-air temperatures at which ice forms on aircraft surfaces. An experimental study was made of the wet-surface temperature and the stream conditions that result in ice-free surfaces for bodies …

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152. NACA-TR-1215 Thermodynamics

     "... the effect on final results of droplets that do not freeze completely on the cylinders"

     

     "Impingement of Cloud Droplets and Procedure for Measuring Liquid-Water Content and Droplet Sizes in Supercooled Clouds by Rotating Multicylinder Method" [Thermodynamics topics] ¹

     Summary

     Conditions where not all water drops freeze are considered.

     Key points

     1. Conditions where not all water drops freeze on the multicylinder instrument are considered.
     2. Rotating cylinder Ludlam limits are compared to flight test data.

     Abstract

     Evaluation of the rotating multicylinder method for the measurement of droplet-size distribution, volume-median droplet size, and liquid-water content in clouds showed that small uncertainties in the basic data eliminate the distinction between different cloud droplet-size distributions and are a source of large errors in the determination of the droplet size. Calculations of the trajectories of cloud droplets in incompressible and compressible flow fields around a cylinder were performed on a mechanical analog constructed for the study …

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153. NACA-TN-3104

     "there has been speculation concerning removing ice during flight in clear air at high altitudes by the process of sublimation"

     "Experimental Investigation of Sublimation of Ice at Subsonic and Supersonic Speeds and its Relation to Heat Transfer" ¹

     

     Abstract

     An experimental investigation was conducted in a 3.84- by 10-inch tunnel to determine the mass transfer by sublimation, heat transfer, and skin friction for an iced surface on a flat plate for Mach numbers of 0.4, 0.6, and 0.8 and pressure altitudes to 30,000 feet. Measurements of rates of sublimation were also made for a Mach number of 1.3 at a pressure altitude of 30,000 feet.
     The results show that the parameters of sublimation and heat transfer were 40 to 50 percent greater for an iced surface than was the bare- plate heat-transfer parameter. For iced surfaces of equivalent roughness, the ratio of sublimation …

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154. NACA-TN-3045

     "The evaporative cooling of surfaces by air streams at high speed is of considerable interest"

     "Analogy Between Mass and Heat Transfer with Turbulent Flow" ¹

     

     Summary

     For turbulent flow on a flat plate, ke/kh is about 1.1 to 1.05.

     Key points

     1. For turbulent flow on a flat plate, ke/kh is about 1.1 to 1.05.
     2. The result applies at Mach numbers up to 1.5.

     Abstract

     An analysis of combined heat and mass transfer from a flat plate has been made in terms of Prandtl's simplified physical concept of the turbulent boundary layer. The results of the analysis show that for conditions of reasonably small heat and mass transfer, the ratio of the mass- and heat-transfer coefficients is dependent on the Reynolds number of the boundary layer, the Prandtl number of the medium of diffusion, and the Schmidt number of the diffusing fluid in the …

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155. NACA-TN-3024

     "evaporation losses are ... very small (less than 1 percent) in the case of smaller obstacles (of icing-rate-measurement-cylinder size)."

     "Maximum Evaporation Rates of Water Droplets Approaching Obstacles the Atmosphere under Icing Conditions" ¹

     

     Summary

     Less that 1% of drops evaporate approaching an obstacle for most cases.

     Key points

     1. Equations are detailed for the evaporation of water drops approaching an obstacle.
     2. Less that 1% of drops evaporate approaching an obstacle for most cases.

     Abstract

     When a closed body or a duct envelope moves through the atmosphere, air pressure and temperature rises occur ahead of the body or, under ram conditions, within the duct. If cloud water droplets are encountered, droplet evaporation will result because of the air-temperature rise and the relative velocity between the droplet and stagnating air. It is shown that the solution of the steady-state psychrometric equation provides evaporation rates which are the maximum possible when droplets are entrained in …

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156. Fraser

     "[LWC] limits have been calculated for a rotating cylinder..., and the results show that rotating cylinder measurements are of limited usefulness and may, in fact, prove entirely misleading as regards both water content and droplet size."

     Fraser, et al., "Thermodynamic Limitations of Ice Accretion Instruments" ¹

     

     Summary

     The term "freezing fraction" is defined (but probably not the one that you expected).

     Key points

     1. The term "freezing fraction" is defined (but probably not the one that you expected).
     2. "Ludlam limits" for instruments are calculated.

     Abstract

     A number of instruments used for determining the supercooled water content of an icing cloud depend on measuring the rate of accretion of ice on an unheated body. It has been shown by Ludlam that, since only part of the supercooled water freezes on impact, and the rest cannot always be frozen by the limited convective and evaporative heat losses which are available, there are limiting …

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157. NACA-TN-2914

     "The effects of frictional heating were analyzed to determine the conditions under which ice formations can be prevented"

     

     NACA-TN-2861 "Analytical Investigation of Icing Limit for Diamond Shaped Airfoil in Transonic and Supersonic Flow" ¹

     and

     NACA-TN-2914 "A Method for Rapid Determination of the Icing Limit of a Body in Terms of the Stream Conditions" ²

     Summary

     The warmest ambient temperature at which ice can accumulate is calculated.

     Key points

     1. The warmest ambient temperature at which ice can accumulate is calculated.
     2. Compressibility effects were included.
     3. Analysis showed good results compared to test data at transonic Mach numbers.

     Abstract

     Calculations have been made for the icing limit of a diamond airfoil at zero angle of attack in terms of the stream Mach number, stream temperature, and pressure altitude. The icing limit is defined as a wetted-surface temperature of 32F and is related to the stream conditions by the method of Hardy.
     The …

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158. A Brief Digression on Unit Systems

     "I'm burning through the sky, yeah. Two hundred degrees, that's why they call me Mister Fahrenheit. I'm travelling at the speed of light."

     from Queen, "Don't Stop Me Now".

     Standard weights and other measurements in use. ¹

     Summary

     The unit system used herein is detailed.

     Preferred units (primary SI units):

         mass: kg
         force: N
         length: m
         tk: temperature, K
         time: seconds, s
         p: air static pressure, Pa (N/m^2)
         u: free-stream air speed, m/s
         altitude: pressure altitude, m
         energy: J or N-m
     

     Icing specific, entrenched exceptions:

         d_drop: water drop diameter, micrometer (1e-6 m)
         lwc: liquid water content, g/m^3
     

     The NACA publications systems of units

     The units in the NACA publications vaguely follow "US Customary" units, although there are often exceptions:

         mass: g, kg, lbm, slug
         force: N, lbf
         length: micron, inch, foot, mile, nautical mile
         temperature: F, R
         time: s, hour
         air static pressure, lbf/in …

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159. NACA-TN-2799

     "Solution of the heat and mass transfer from a wetted surface is quite involved and tedious."

     "Simple Graphical Solution of Heat Transfer and Evaporation from Surface Heated to Prevent Icing" ¹

     

     Figure 1. - Graphical solution of anti-icing heat and mass transfer from surface subject to impingement and heated above freezing.

     Summary

     Simplified ice protection equations allow graphical solutions.

     Key points

     1. Simplified ice protection equations allow graphical solutions.
     2. The effects of varying local surface pressure and velocity are included.

     Abstract

     Equations expressing the heat transfer and evaporation from wetted surfaces during ice prevention have been simplified and regrouped to permit solutions by simple graphical means. Working charts for quick and accurate anti-icing calculations are also included.

     Discussion

     INTRODUCTION Solution of the general problem of heat and mass transfer from a wetted surface in forced convection is quite involved and tedious. The calculations that often must be made point by point along …

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160. Python coding style guide

     "Beautiful is better than ugly."

     

     Summary

     For the Thermodynamics tread and on, I will be using this style guide. Previous code may eventually be upgraded to this.

     Python target version:

     Target python version 3.7, and the corresponding Anaconda stack (version 2021-11). Avoid modules with deprecation warnings (there are not many of them). This is a balance between current installations and future-proofing. The goal is to be applicable for all 3.7+ uses.

     (Note: 3.10 is the latest available version, as of April 2022).

     Code should be portable, and not use operating system specific functions.

     General guidelines

     • simple

       • use simple functions over classes
       • out-source complexity where possible
         • use built-in data structures (list, dict)
         • use numpy and scipy, anything in the anaconda stack
       • promote reuse
         • anything used more than once should be put in an importable module
         • use the "if __name__ == '__main__:" block idiom
           • to have clean (no side effect …

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161. Messinger

     ""freezing-fraction" denotes the proportion of the impinging liquid which freezes in the impingement region"

     B. L. Messinger, "Equilibrium Temperature of an Unheated Icing Surface as a Function of Airspeed" ¹

     

     Modes of energy transfer for an unheated airfoil in icing conditions.

     Summary

     The term "freezing fraction" is defined

     Key points

     1. Heat balance equations for a wet surface are presented.
     2. The term "freezing fraction" is defined
     3. Example calculations are provided
     4. Icing wind tunnel test data is provided

     Abstract

     The thermal analysis of a heated surface in icing conditions has been extensively treated in the literature. Except for the work of Tribus, however, little has been done on the analysis of an unheated icing surface. This latter analysis is significant in the design of cyclic thermal deicing systems that are attractive for small high-speed aircraft for which thermal anti-icing requirements have become severe. In this paper, a complete analysis of the temperature …

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162. Ludlam

     "The rotating-cylinder technique of determining water content and drop-size distribution cannot therefore be used without consideration of the heat economy"

     

     F. H. Ludlam, "The Heat Economy of a Rimed Cylinder" ¹

     Summary

     Various "Ludlam Limits" have been implemented, but they produce different results.

     Key points

     1. Calculations are laid out for finding the "critical" LWC where not all available water freezes on a cylinder.
     2. The critical LWC is often termed the "Ludlam limit", although Ludlam did not use that term.
     3. Various "Ludlam Limits" have been implemented, but they produce different results.

     Abstract

     A method is described for calculating the surface temperature of a slender cylinder which is moved through a supercooled cloud and becomes covered with rime ice. When the surface temperature reaches 0°C the ice formation proceeds at the maximum possible rate; the associated liquid-water content of the cloud is calculated and found to be usually less than the …

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163. NACA-TN-1472

     "... equations for calculating the rate of heat transfer from airfoils in icing conditions were verified"

     "The Calculation of the Heat Required for Wing Thermal Ice Prevention in Specified Icing Conditions" ¹

     

     Summary

     Natural icing flight tests with an instrumented test airfoil are compared to 2D thermodynamic calculations.

     Key points

     1. Thermodynamic equations for a heated surface with water impingement are detailed.
     2. Test flights in natural icing conditions measured surface temperature for a heated surface.
     3. Runback water characteristics were noted.
     4. Heat transfer coefficients in icing were be inferred from measurements and calculations.
     5. "the design of heated wings on a fundamental, wet-air basis now can be undertaken with reasonable certainty."

     Abstract

     As a result of a fundamental investigation of the meteorological conditions conducive to the formation of ice on aircraft and a study of the process of airfoil thermal ice prevention, previously derived equations for calculating the rate of heat transfer from airfoils …

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164. NACA-TR-831

     "It has been shown that the temperature of the surface of the wing in conditions of icing can be predicted with considerable exactitude from the temperatures measured in clear air."

     "An Analysis of the Dissipation of Heat in Conditions of Icing from a Section of the Wing of the C-46 Airplane" ¹

     

     Summary

     Two-dimensional heat balance equations for ice protection are detailed.

     Key points

     1. Heat balance equations for ice protection are detailed.
     2. An assumption about water drop temperature approaching an object is made.
     3. A cylinder approximation for an airfoil leading edge is used for water drop impingement.

     Abstract

     A method is given for calculating the temperature that a surface, heated internally by air, will assume in specified conditions of icing. The method can be applied generally to predict the performance, under conditions of icing, of the thermal system for protecting aircraft. Calculations have been made for a section of the …

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165. NACA-ARR-5G13

     "A method is given for calculating the temperature of a surface wetted ... by a pure liquid, such as water"

     "Kinetic Temperature of Wet Surfaces A Method of Calculating the Amount of Alcohol Required to Prevent Ice, and the Derivation of the Psychrometric Equation" ¹

     

     Summary

     Psychrometric equations are presented to calculate the thermal effects of evaporation from wet surfaces at high air speeds.

     Key Points

     1. The wet surface equilibrium "datum" temperature is defined.
     2. Psychrometric equations are presented to calculate the thermal effects of evaporation from wet surfaces.
     3. The calculations are implemented in python code.

     Abstract

     A method is given for calculating the temperature of a surface wetted either by a pure liquid, such as water, or by a mixture, such as alcohol and water. The method is applied to the problem of protecting, by alcohol, propellers and the induction system of the engine against ice. The minimum quantity of alcohol …

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166. Icing Thermodynamics

     "ice formation can be redefined in more general terms as a thermodynamic problem" ¹ (1936)

     

     Icing Thermodynamics Thread

     Summary

     This thread will focus on the use of thermodynamic heat and mass balance for icing and ice protection calculations.

     There may be some overlap with ice protection systems, but the systems will not be detailed herein.

     NACA-ARR-5G13, Kinetic Temperature of Wet Surfaces A Method of Calculating the Amount of Alcohol Required to Prevent Ice, and the Derivation of the Psychrometric Equation."

     Psychrometric equations are presented to calculate the thermal effects of evaporation from wet surfaces.

     NACA-TR-831, An Analysis of the Dissipation of Heat in Conditions of Icing from a Section of the Wing of the C-46 Airplane

     Two-dimensional heat balance equations for ice protection are detailed.

     NACA-TN-1472, The Calculation of the Heat Required for Wing Thermal Ice Prevention in Specified Icing Conditions

     Natural icing flight tests with an instrumented test airfoil …

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167. Conclusions of the Cylinder Thread

     "The collection of ice by the cylinders is similar to the collection of ice by airplane components." ¹

     

     Summary

     Data from the post-NACA era are used to resolve open questions

     Key points

     1. The Cylinders thread is summarized
     2. Post-NACA era data is used to resolve some open questions.
     3. NACA era data that are still used today are summarized

     Discussion

     Review of the Cylinders thread so far

     In the Cylinders thread, we saw:

     • A pioneering analysis of water drop impingement on a cylinder (NACA-TN-779)
     • The most cited aircraft icing publication, with more detail of water drop impingement on a cylinder, and the rotating multicylinder instrument ("Mathematical Investigation of Water Droplet Trajectories")
     • In flight icing measurements and an icing severity index (NACA-TN-1393)
     • An additional way to estimate drop size on a fixed cylinder (NACA-TN-1424)
     • Nine icing instruments compared (NACA-RM-A9C09)
     • The ability of the multicylinder method to determine drop distribution was questioned several times …

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168. NACA-TN-3338

     "a method has been developed ... to determine the droplet size distribution of the impinging cloud"

     "A Dye-Tracer Technique for Experimentally Obtaining Impingement Characteristics of Arbitrary Bodies and a Method for Determining Droplet Size Distribution" ¹

     Summary

     A pioneering test method is described, and a drop size measurement analysis is proposed.

     Key points

     1. A dye-tracer blotter-paper water drop impingement measurement technique is described.
     2. An analysis of test results to determine the water spray drop size distribution is described.
     3. The analysis method accuracy is unknown due to the lack of an independent measurement of drop sizes.
     4. We see the use of the Icing Research Tunnel for the first time in the Cylinders thread.

     Abstract

     A dye-tracer technique has been developed whereby the quantity of dyed water collected on a blotter-wrapped body exposed to an air stream containing a dyed-water spray cloud can be colorimetrically determined in order to obtain local collection efficiencies …

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169. NACA-TR-1215

     "... the effect on final results of droplets that do not freeze completely on the cylinders"

     

     "Impingement of Cloud Droplets and Procedure for Measuring Liquid-Water Content and Droplet Sizes in Supercooled Clouds by Rotating Multicylinder Method." ¹

     Summary

     Conditions where not all water drops freeze are considered.

     Key points

     1. NACA-TN-2903, NACA-TN-2904, and NACA-RM-E53D23 are "superseded" (collected together).
     2. Conditions where not all water drops freeze on the multicylinder instrument are considered.
     3. The terms "freezing fraction" is introduced into the NACA publications.

     Abstract

     Evaluation of the rotating multicylinder method for the measurement of droplet-size distribution, volume-median droplet size, and liquid-water content in clouds showed that small uncertainties in the basic data eliminate the distinction between different cloud droplet-size distributions and are a source of large errors in the determination of the droplet size. Calculations of the trajectories of cloud droplets in incompressible and compressible flow fields around a cylinder were performed on a …

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170. NACA-RM-E53D23

     "The meteorological data obtained with the multicylinder method are the only data available for the design of ice-protection equipment for aircraft"

     "Procedure for Measuring Liquid-Water Content and Droplet Sizes in Super-cooled Clouds by Rotating Multicylinder Method"¹

     

     Summary

     Detailed procedures for the use of multicylinders are described.

     Key points

     1. Detailed procedures for the in-flight use of multicylinders are described.
     2. Detailed procedures for analyzing results from of multicylinders are described, with a flight data case.
     3. Differences in analysis method details can drive MVD and LWC differences in the range of 5% to 10%.

     Abstract

     The rotating multicylinder method for in-flight determination of liquid-water content, droplet size, and droplet-size distribution in icing clouds is described. The theory of operation, the apparatus required, the technique of obtaining data in flight, and detailed methods of calculating the results, including necessary charts and tables, are presented.

     Discussion

     Procedures

     A set of rotating cylinders were constructed …

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171. NACA-TN-2903

     "For most practical problems involving measurements of droplet impingement on cylinders, the compressibility effect may be ignored."

     "Impingement of Cloud Droplets on Aerodynamic Bodies as Affected by Compressibility of Air Flow Around the Body"

     Summary

     The effect of the compressibility of air on the water-drop impingement calculations is found to be "negligible".

     Key points

     1. The effect of the compressibility of air on the water-drop impingement calculations is found to be "negligible"

     Abstract

     The trajectories of water droplets in a compressible-air flow field around a cylinder were computed with a mechanical analog. The results of the calculations at approximately the flight critical Mach number were compared with calculations of trajectories in an incompressible flow field. For a cylinder, the effect of compressibility of the air on the droplet trajectories was negligible up to the flight critical Mach number. The results obtained with the cylinder were extended to airfoils. This extension is …

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172. NACA-TN-2904

     "Many data points were carefully calculated in order to determine precisely the rate of droplet impingement on the surface of a right circular cylinder."

     

     "Impingement of Water Droplets on a Cylinder in an Incompressible Flow Field and Evaluation of Rotating Multicylinder Method for Measurement of Droplet-Size Distribution, Volume-Median Droplet Size, and Liquid-Water Content in Clouds" ¹

     Summary

     Detailed water drop impingement analysis (independent of prior analysis) is presented.

     Key points

     1. Detailed water drop impingement analysis (independent of prior analysis) is presented
     2. Error estimates are detailed.
     3. Detailed Beta curves are provided.
     4. A difference from Langmuir and Blodgett for drop size distributions calculations is noted.

     Abstract

     Evaluation of the rotating multicylinder method for the measurement of droplet-size distribution, volume-median droplet size, and liquid-water content in clouds shoved that small uncertainties in the basic data eliminate the distinction between different cloud droplet-size distributions and are a source of large errors in the determination …

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173. A Langmuir B drop size distribution is (almost) a normal distribution

     "Upon comparing this chart with Langmuir's tables, it was found that his selections of the representative radii for the various sub-divisions of the volume were in error." ¹

     Summary

     The Langmuir B drop size distribution is almost a normal distribution.

     Key points

     1. The Langmuir B drop size distribution is almost a normal distribution.
     2. Perhaps it was originally intended that it be exactly a normal distribution.
     3. The proposed alternatives in NACA-TN-2708 appears to have larger errors, rather than correcting errors.
     4. The other Langmuir distributions (C, D, E) do not fit a normal distribution as well.

     Discussion

     Normal drop size distributions

     Normal distributions show up many places in nature, so it is not surprising that drop sizes in clouds can approximate a normal distribution.

     In NACA-TN-2708 ¹, it was "presumed" that water-volume distribution with the drop size is a Gaussian [normal] distribution:

     Drop-Size Distribution. - In the present report it is presumed, following …

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174. NACA-TN-2708

     "...At low airspeeds and with large cylinders, the determination should be relatively good."

     "Comparison of Three Multicylinder Icing Meters and Critique of Multicylinder Method" ¹

     Summary

     Multicylinder instruments had good agreement for liquid water content and median effective drop diameter, but poor agreement for the distribution type.

     Key points

     1. Three multicylinder instruments had good agreement for liquid water content and median effective drop diameter, but poor agreement for the distribution type
     2. The Langmuir drop size distributions were revised (but the revised versions were not widely adopted)

     Abstract

     Three multicylinder cloud meters, fundamentally similar but differing in important details, were compared in use at the Mount Washington Observatory. Determinations of liquid water content were found to agree within the limits of the probable error, but the two instruments designed by the National Advisory Committee for Aeronautics indicated larger drop sizes than did the Observatory's instrument, apparently because of spurious ice catch …

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175. NACA-TN-1904

     "... the rotating-cylinder indications of drop-size distribution are so unreliable that they are of little or no value"

     NACA-TN-1904, "Observations of Icing Conditions Encountered in Flight During 1948" ¹

     Summary

     Meteorological data from flight observations in icing conditions during the first 5 months of 1948 are presented.

     Key points

     1. The average liquid water content varies over distance traveled in icing.
     2. The value of the multicylinder method for determining drop size distributions is questioned.
     3. Other flight test instruments are described.

     Abstract

     Meteorological data from flight observations in icing conditions during the first 5 months of 1948 are presented. A total of 335 measurements of liquid-water content and mean-effective drop diameter were obtained by the multicylinder method in the course of 40 flights in icing conditions covering most of northern United States. Cumulus clouds were predominant during approximately two-thirds of the flights. A continuous record of liquid-water content covering a major portion of …

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176. The Greatest Thing That You Have (Probably) Never Read: AC 00-6A (Cancelled)

     "Aircraft icing is one of the major weather hazards to aviation. Icing is a cumulative hazard. It reduces aircraft efficiency by increasing weight, reducing lift, decreasing thrust, and increasing drag." ¹

     Summary

     Prior information from the FAA on "Aviation Weather For Pilots and Flight Operations Personnel".

     Discussion

     Veteran pilots with FIKI ratings (Flight In Known Icing) may already be familiar with this, but the rest of us could benefit from reading it.

     Alas, this was cancelled in 2016 (the next version calcelled in 2022 ², and the superseding version ³ is more current, but not as entertaining a read). It also features "instructive illustrations" to introduce each chapter, which are somewhere on the corney-questionable-objectionable spectrum.

     The potential hazards of structural icing are noted:

     I am not so sure about the "Stalling Speed Increases" part. The speed at which the airplane may stall at may decrease due to the effects of …

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177. NACA-RM-A9C09

     "The [multicylinder] method has assumed the position of a standard against which other instruments are calibrated, and is apt to remain so..."

     

     "A Review of Instruments Developed for the Measurement of the Meteorological Factors Conducive to Aircraft Icing"

     ¹

     Summary

     The multicylinder is the "standard against which other instruments are calibrated"

     Key points

     1. Nine instruments, including the fixed cylinder and rotating multicylinder, are qualitatively assessed.
     2. "The [multicylinder] method has assumed the position of a standard against which other instruments are calibrated, and is apt to remain so..."
     3. The effect of mass measurements errors on multicylinder results were assessed.
     4. "A reliable method for the measurement of drop-size distribution should be developed"

     Abstract

     The status of instrument suitable for the measurement of the meteorological factors conducive to aircraft icing is reviewed. The meteorological factors to be evaluated are listed, and tentative values for the desired and acceptable accuracy of measurement for each …

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178. The Historical Selected Bibliography of NACA-NASA Icing Publications

     "... the recommendation was made that before attacking what appeared to be a new icing problem we should study the icing work of the 1940's and 50's." ¹

     
     The cover page of NACA-TN-2569. The original covers were often this orange or yellow, with some in beige or blue. If you find an original print now the color is probably rather faded.

     Summary

     A "Selected Bibliography of NACA-NASA Icing Publications" identified 132 publications in 17 categories.

     Discussion

     Publications

     This title was published three times.

     The first was in 1969 in the "Aircraft Ice Protection Report of Symposium" ¹ as "Selected Bibliography of NACA-NASA Unclassified Icing Publications". It was not credited, but immediately followed a paper by Vernon Gray.

     The second publication was in 1971 as part of FAA Advisory Circular 20-73 "Aircraft Ice Protection" ², as "APPENDIX 2. SELECTED BIBLIOGRAPHY OF UNCLASSIFIED NASA-NACA AIRCRAFT ICING REPORT". It was not otherwise credited. It …

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179. NACA-TN-1424

     "In spite of the inconsistency it is believed that the data on mean-effective diameters are fairly reliable."

     "A Further Investigation of the Meteorological Conditions Conducive to Aircraft Icing" ¹

     Summary

     The value of the multicylinder data for determining drop size distribution is questioned.

     Key points

     1. Two methods for determining drop size distributions are compared.
     2. The difference in water drop concentration around an aircraft body is proposed as an explanation for results from the two methods.
     3. A temperature effect of icing conditions is noted.
     4. Previously proposed design values from NACA-TN-1393 were verified.

     Abstract

     Meteorological data from flight observations in icing conditions during the winter of 1946-47 are presented. Data on liquid water content, temperature, and mean-effective drop diameter are shown to be consistent with values previously proposed for maximum icing conditions. Data on drop-size distribution as obtained by the rotating-cylinder method, although consistent with measurements previously made, were found to be …

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180. NACA-TN-1393

     "The rotating-cylinder method of measuring liquid water content is generally regarded as being the most accurate and dependable procedure thus far developed"

     

     “A Flight Investigation of the Meteorological Conditions Conducive to the Formation of Ice on Airplanes"

     ¹

     Summary

     A multicylinder and other instruments measure natural icing conditions in flight.

     Key points

     1. The accuracy of multicylinder instruments used to determine liquid water content and median water drop size is assessed.
     2. An icing intensity index as related to the ice growth rate on a 3-inch diameter cylinder is detailed.
     3. Results from agree well with the Python implementation of the cylinder analysis.
     4. "Tentative" values for icing design conditions were determined.
     5. An effect of distance on icing conditions is noted.

     Abstract

     Data from flight measurements of the meteorological factors related to the intensity of icing conditions are presented. The physical factors that establish the distribution of liquid water in clouds of various types …

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181. Implementation of multicylinder calculations in Python

     "This effect would be expected if the droplets were of non-uniform size, since the largest droplets could reach the largest collector while those of average size could not." ¹

     Summary

     The calculations to determine drop median volumetric diameter with a multicylinder instrument are implemented in Python.

     Key points

     1. A manual method of multicylinder calculation is illustrated.
     2. The drop median effect diameter is reproduced well from a multicylinder example in "Mathematical Investigation of Water Droplet Trajectories"

     Discussion

     Manual method of drop size analysis

     By measuring the differential rates of ice collection on cylinders of different sizes the drop median volumetric diameter (MVD) can be determined.

     Some typical multicylinder instruments (from NACA-TN-2708 ¹):

     "Mathematical Investigation of Water Droplet Trajectories" ² provides an example of the multicylinder calculations method in the section "Example of the Application of the D.A. Data to Experimental Data".

     The method has been revised as a result of …

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182. A Detailed Comparison of Water Drop Impingement Calculations

     "The discrepancies are of the magnitude to be expected from ... the step by step integration"

     Summary

     Water drop impingement calculations on a cylinder from "Mathematical Investigation of Water Droplet Trajectories" ¹ and NACA-TN-779 ² are compared.

     Key Points

     1. There are differences in conditions in Table IV(a) of "Mathematical Investigation of Water Droplet Trajectories" compared to NACA-TN-779.
     2. When the conditions are revised to match, the comparison with NACA-TN-779 data improves.

     Discussion

     NACA-TN-779

     In NACA-TN-779, the water drop impingement on a cylinder 12 inch in diameter, with an airspeed of 200 mph, was analyzed. The altitude was not noted. Water drop diameters from 0.002 inch (about 8 micrometer) to 0.1 inch (about 4000 micrometer) were considered, as shown below.

     

     The “swept area of cleared drops” represents what fraction of the water drops in the forward projected area of the cylinder impinge on the cylinder. In more modern terms, this …

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183. Implementation of cylinder impingement correlations in Python

     "The equations were found to fit the experimental data over a wider range of values..." ¹

     Summary

     The correlations for water drop impingement on a cylinder from "Mathematical Investigation of Water Droplet Trajectories" ¹ are implemented in the Python programming language.

     Key points

     1. The cylinder impingement correlations were implemented and reproduced values from "Mathematical Investigation of Water Droplet Trajectories"
     2. A subtlety about calculations with drop size distributions is noted.

     Discussion

     Implementation of cylinder impingement correlations

     Alas, I do not have access to a differential analyzer as was used in ¹, so I will have to use a modern, digital computer. Also, we will not be integrating the water drop equations of motion; we will be using the data in ¹ to determine water drop impingement on a cylinder.

     The Anaconda distribution of Python version 3.7 was used ², as this includes the third party modules matplotlib, numpy, and scipy …

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184. "Mathematical Investigation of Water Droplet Trajectories"

     "IT IS DESIRED to calculate the trajectories of small water droplets (fog) in air moving at high velocities across a cylinder."

     

     Summary

     Langmuir drop size distributions are defined, and water drop impingement on a collection of cylinders for use as an icing instrument is described.

     Key points

     1. The Langmuir drop size distributions are defined
     2. The water drop impingement terms E, Beta, K, and Ko are defined
     3. The use of cylinders of different sizes and detailed calculations to determine water drop sizes

     Abstract

     Calculations are given of the trajectories of small water droplets moving in air at high velocities across a cylinder. The calculations were made by means of a differential analyzer (D.A.). A few calculations are also given for the case of a sphere and a ribbon.

     Each D. A. trajectory represents the motion of a single particle. The theoretical curves for the efficiency of deposition of very large …

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185. NACA-TN-779

     "In order to provide qualitative information ..., numerical calculations of the drop paths in air flowing ... around a circular cylinder were made"

     

     “Aerodynamic Heating and Deflection of Drops by an Obstacle in an Airstream in Relation to Aircraft Icing"

     Summary

     Water drop impingement on a cylinder is calculated.

     Key points

     1. The effect of aerodynamic heating is predictable
     2. The impingement of water drops on a cylinder is calculated

     Abstract

     Two topics of interest to persons attempting to apply the heat method of preventing ice formation on aircraft are considered. Surfaces moving through air at high speed are shown, both theoretically and experimentally, to be subject to important aerodynamic heating effects that will materially reduce the heat required to prevent ice.

     Numerical calculations of the paths of water drops in an air stream around a circular cylinder are given. From these calculations, information is obtained on the percentage of the swept area cleared …

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186. NACA Icing Publications Database

     "The documents of that period were so old, however, that they were not listed in the modern computerized library search systems" ¹

     
     NACA Cleveland library, circa 1945.

     Summary

     210 NACA icing publications were identified, and the references were included in a database.

     Discussion

     I have assembled a database of 210 NACA-NASA* icing publications. 132 were cited in “Selected Bibliography of NACA-NASA Aircraft Icing Publications” ¹. I also identified 78 additional NACA icing publications in the NTRS ² that were not cited in ¹.

     The format of the citations in the NACA publications varies over the years. For the database, the citations were updated to a consistent format similar to MLA format (similar to that used in current NASA publications).

     The document identifiers such as “NACA TN 1907” were updated to the format used in the NTRS, such as “NACA-TN-1907”.

     Some publications were written concurrently with other publications, so the citation …

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187. Icing on Cylinders

     "The collection of ice by the cylinders is similar to the collection of ice by airplane components." ¹

     

     
     Calculating water drop trajectories with a differential analyzer analog
     (from NACA-TN-2904)

     Summary

     The cylinder has a wide range of current uses in aviation

     Abstract

     The cylinder has a wide range of current uses in aviation:
     - Meteorological instruments for flight and icing wind tunnel tests
     - Aircraft in-flight ice detectors and indicators
     - Structural elements (such as landing gear and cables)
     - An approximation of an airfoil leading edge (used in thermal design and icing wind tunnel test conditions determination ²)

     Icing conditions measurements with instruments based on cylinders were key to developing the current aircraft flight in icing certification regulations.

     One hundred and thirty-two NACA publications related to aircraft icing were identified in "The Historical Selected Bibliography of NACA-NASA Icing Publications", and categorized into 17 topics.

     Publications related to icing on a …

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188. More general information

     
     

     Here are references that include more general information on the NACA era and aircraft icing.

     Lew Rodert, Epistemological Liaison, and Thermal De-Icing at Ames

     "We Freeze to Please": A History of NASA's Icing Research Tunnel and the Quest for Flight Safety

     "Bringing the Future Within Reach: the NASA John H. Glenn Research Center"

     "The Wind and Beyond: Journey into the History of Aerodynamics in America, Volume 2, Reinventing the Airplane.", NASA-SP-4409, 2007. (Especially the "Heat Against Ice" excerpt, p. 506-518.)
     history.nasa.gov

     "Engines and Innovation: Lewis Laboratory and American Propulsion Technology". NASA SP-4306, by Virginia P. Dawson, 271 pages, published by NASA, Washington, DC, 1991 4306 (1991) ntrs.nasa.gov, especially the chapter "Operations Research".

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189. About

     

     This site is still under development.

     Do not expect the site content, structure, nor links to be stable.

     Author: Donald E. Cook

     Welcome

     A Gentle Introduction to Aircraft Icing

     Six Month Review

     One Year Review

     Web publishing tools

     Python programming style guide

     Ideas for Future Posts

     The Blast from the Past Newsletter

     The web content is hosted at two, mirrored sites: icinganalysis.github.io
     icinganalysis.com

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190. Diversions

     
     Four Instructive Illustrations.

     Diversions can take us into the post-NACA era of aircraft icing, with perhaps more freewheeling reviews.

     The Greatest Thing That You Have (Probably) Never Read: AC 00-6A

     The Greatest Thing That You Have (Probably) Never Read: 1969 Aircraft Ice Protection Report of Symposium

     The Greatest Thing That You Have (Probably) Never Read: Wilder, Ramon W.: "Techniques used to determine Artificial Ice Shapes and Ice Shedding, Characteristics of Unprotected Airfoil Surfaces"

     A Brief Digression on Units

     Instructive Illustrations

     Out-Sourcing My Work to ChatGPT and DALL-E ;)

     Candidates (not yet reviewed):

     • Green, Steven D.: Inflight Icing Education Objectives for Air Carrier Pilots, AIAA 2003-21, 2003. http://www.flightopsresearch.org/data/files/aiaa2003-21.pdf.
     • NACA Conference on Aircraft Ice Prevention A Compilation of Papers Presented by NACA Staff Members. 6505/NACA-1947/8, 1947.
       This is available at DTIC.
     • Project Cirrus, Final Report, 1948
     • Mazin, I. P., 1957: The Physical Principles of …

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191. Donald Cook

     
     Making delicate adjustments in an icing wind tunnel.

     Donald Cook has over 30 years experience at a major airplane manufacturer in several areas of aircraft icing, including:

     • Ice shape analysis (including computational fluid dynamics tool development)
     • Ice protection system design, test, analysis, and certification
       • wing anti-ice
       • engine anti-ice
       • air data probes
       • ice detection
     • Natural icing flight test
     • Icing wind tunnel test
     • Industry groups
     • Teaching classes on aircraft icing
     • Certification
     • Regulatory issues

     BS Engineering Iowa State University
     MS Engineering University of Wisconsin

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192. Web publishing tools

     
     Linotype operators circa 1942. Public Domain Library of Congress.

     The Python package Pelican ¹ was used to build this web page.

     The Markdown ² markup text format was used to write the content.

     The Python package matplotlib and LibreOffice Impress ³ were used to produce graphics.

     The content is hosted on GitHub Pages ⁴ icinganalysis.github.io.
     There is also a mirror site icinganalysis.com.

     Notes:

     ---

     1. blog.getpelican.com ↩

     2. daringfireball.net ↩

     3. libreoffice.org ↩

     4. docs.github.com ↩

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193. Welcome

     “If you want to go somewhere, it’s best to find someone who has already been there” Robert Kiyosaki

     

     Many new aircraft icing problems aren’t new at all. Like excavating a lost city, many surprises, answers to problems, road maps, and confirmations can be found in the work of the National Advisory Committee for Aeronautics (NACA). This treasure trove of data can help you today.

     Why care about aircraft icing? If ice forms on a plane during flight, it can be hazardous. Engineers research the weather conditions aircraft will encounter and work to ensure that they can navigate them safely.

     What you will find here

     On this website, I make selected NACA publications easily accessible to you. I have read thousands of pages so that you do not have to.

     I summarize each paper for you with:
     - a quote from the paper
     - a one-line summary
     - the …

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