Articles with tag: "basics"

1. 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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2. 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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3. 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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4. 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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5. 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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6. 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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7. 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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8. 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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9. 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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