Articles with tag: "intermediate topics"

1. 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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2. 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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3. 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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4. 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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5. 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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6. 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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7. 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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8. 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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9. 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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10. 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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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. 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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13. 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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