Articles with tag: "meteorology"

1. 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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2. 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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3. 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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4. 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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5. 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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6. 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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7. 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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8. 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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9. 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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10. 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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11. 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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12. 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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13. 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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14. 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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15. 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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