Articles with tag: "ice shapes"

1. Swept Airfoil Cases in IceVal

   "Use of these relationships allows the direct determination of ice shapes adjusted for any given icing and flight condition as well as for size and sweep of the airfoil" ¹

   
   

   Experimental ice shapes compared to a LEWICE analysis.

   Summary

   There are 41 swept airfoil cases in the IceVal database ².

   The quote at the top from Wilder briefly describes the the empirically based analytical method he described in ¹. However, it is not directly applicable to airfoils other than the ones he considered, which had dozens of icing tunnel ice shapes tests each. For more details on Wilder's method, see Wilder.

   LEWICE ³, and other codes, offer potentially more widely applicable methods of ice shape prediction in swept airfoils.

   LEWICE analysis for these cases tends to produce ice shapes that are consistently too small compared to experiment.

   Empirically derived adjustments to the inputs to LEWICE are discussed that improve the …

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2. Running LEWICE version 3.2.3 for the IceVal cases

   "The resulting analysis showed that LEWICE compared well to the available experimental data." ¹

   
   

   An example of a good comparison between analysis and experiment.

   Introduction

   The IceVal database ², and its predecessors, were originally assembled to validate the LEWICE ³ ice shape prediction code.

   Here, we will repeat that analysis with a more recent version of LEWICE, and look at the effects of using "corrected" angle of attack values in the analysis.

   The LEWICE ice shapes results in the IceVal database were apparently run with LEWICE version 3.2.2 (We will abbreviate that as the Database LEWICE shape). The IceVal users guide is not explicit, other than "the latest version of the LEWICE ice shape prediction code". The 2008 LEWICE validation report was written at about the same time. It does not mention IceVal, but the validation report was for LEWICE version 3.2.2.

   Comparisons with all IceVal …

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3. A Geometric Analysis Method

   "This demonstrates that the automated process cannot (yet) be substituted for good engineering judgment."

   From the LEWICE manual. ¹

   
   

   A case where two methods detected similar upper surface ice horns.

   Introduction

   Reviewing 6000+ ice shape assessments to verify that they agree with engineering judgement is a daunting task. Even with professionalism and due-diligence, debatable results may be missed. So, there is motivation to automate the process as much as possible.

   Here, I describe a step toward that goal. It is a work in progress, not a completed product.

   Using the IceVal database to validate an assessment method

   The IceVal database will be used here to validate a different comparison assessment method. This is one of the uses envisioned when compiling the database ²:

   ... by compiling a comprehensive database consisting of a standardized, reliable data set, and combining that with an easy-to-use graphical user interface (GUI), providing quick and easy access …

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4. Overall comparison assessments between experiment and LEWICE

   "It is possible for any (or all!) ... parameters to be incorrectly output."

   
   

   A case with identified horn locations that are debatable.

   Introduction

   Assessments of LEWICE ice shapes compared to experiment have been published twice.

   The LEWICE THICK utility program was uses to identify ice horn locations and maximum heights. However, engineering judgement was used to adjust some values in the IceVal database. Cases with questionable ice horn identifications can be found in the database.

   The difficulty of consistently identifying ice horns affects the comparison assessment between LEWICE and experiment.

   Published assessments

   The overall comparison of LEWICE ¹ analysis to experimental data to has been published twice.

   The first was in 1999 ², and included 800 experiment cases. The second was in 2008 ³, and had more than 3000 experimental cases. These are the data that are included in the IceVal database ⁴.

   The 1999 Assessment

   The assessment published in 1999 …

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5. Challenges Using the IceVal Database

   "No data is clean, but most is useful."

   attributed to Dean Abbott.

   
   

   Ice shape tracing points that are mis-ordered and mis-aligned with the airfoil.

   Introduction

   The IceVal database is a significant achievement that is still yielding dividends, decades later.

   The IceVal description ¹ discusses some of the challenges of assembling the database:

   While all of this data is available, in theory, for every test run, as a practical matter, this is often not the case. Because the data is managed by the individual researcher, and much of it is stored in hardcopy form, locating a specific data set may require a significant effort. Furthermore, because of differences in experimental technique from one researcher to the next, the extent to which the relevant conditions have been explicitly documented can vary widely. Moreover, since plans made prior to a test may change during the test based on interim results, it is not …

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6. A Tour of the IceVal DatAssistant

   "... all publicly available IRT-generated experimental ice shapes with complete and verifiable conditions have now been compiled into one electronically-searchable database"

   NASA Report E-16236 ¹.

   
   Public Domain image from NASA Report Number: E-16236.

   A quick tour of the IceVal DatAssistant

   The IceVal DatAssistant is available from NASA. It runs on the Windows operating system (only).

   The IceVal DatAssistant can do several functions. The main interest here is the database of experimental run conditions and results.

   The tables of primary interest are IceShapeData, RunSpecs, and SprayConditions.

   
   Public Domain image from NASA Report Number: E-16236.

   In the time span 1988 to 2008 that the database covers, experimental test results were measured by cutting a thin slot into the ice, inserting a pre-made cardboard template, and manually tracing the ice shape. These were later digitized, and included in the database.

   
   Public Domain image from NASA Report Number: E-16236.

   Range of conditions tested

   The primary …

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7. 6000 Ice Shapes - the IceVal DatAssistant

   "As with any scientific endeavor, the foundation of icing research ... is the data acquired during experimental testing."

   NASA Report E-16236 ¹.
   
   

   
   

   4132 ice shapes for the NACA0012 airfoil.

   [Yes, that is how it is spelled.]

   The IceVal DatAssistant ¹, ² from NASA contains 6330 ice shapes from experiments in the NASA Icing Research Tunnel ³ (3665 shape tracings) and from analysis with LEWICE ⁴ (2965 ice shapes).

   Significant uses of the data were the LEWICE validation reports published in 1998 ^{5 6} and 2008 ⁷, which established measures for the comparison of LEWICE analysis results to experimental data.

   These data are tremendous aids to researchers and developers of icing analysis codes and test methods. It has been 27 and 18 years since these were published (respectively), and we should celebrate that the utility of the data has held up well. However, given that an entire generation of workers in the …

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8. 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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9. 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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10. 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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11. 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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12. 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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13. 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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14. 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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15. 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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16. 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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17. 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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18. 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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19. 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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20. 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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21. 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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22. 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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23. 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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24. 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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25. 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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26. 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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27. 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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