Articles with tag: "ice shapes"

1. 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 …

   read more

2. 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 …

   read more

3. 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 …

   read more

4. 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 …

   read more

5. 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 …

   read more

6. 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 …

   read more

7. 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 …

   read more

8. 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 …

   read more

9. 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 …

   read more

10. 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 …

    read more

11. 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 …

    read more

12. 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 …

    read more

13. 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 …

    read more

14. 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 …

    read more

15. 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 …

    read more

16. 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 …

    read more

17. 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 …

    read more