FM_LiftDrag.cpp

//==================================================================
/// FM_LiftDrag.cpp
///
/// Created by Davide Pasca - 2017/6/12
/// See the file "license.txt" that comes with this project for
/// copyright info.
//==================================================================

#include "stdafx.h"
#include "FM_Utils.h"
#include "FM_LiftDrag.h"

//#define USE_HFFM_FALCOM_REFERENCE
#define TEMP_NICE_F16_CL_AOA0

//==================================================================
namespace FM
{

static constexpr float SSONIC_MACH_REF_VAL = 1.2f;

//==================================================================
LiftDrag::LiftDrag()
{
    { // F-16
    auto &m = mModels[TYPE_F16];

    // see: http://www.kdu.ac.lk/proceedings/irc2015/2015/eng-012.pdf
    m.mRefSurfaceArea = 27.87f;

#ifdef USE_HFFM_FALCOM_REFERENCE
    // see: http://www.dept.aoe.vt.edu/~mason/Mason_f/F16S04.pdf
    // http://www.checksix-fr.com/downloads/falcon4/Topolo/zip/H-F-F-M-manual.pdf (p.15)
    m.mCL_Subso.AddLinearMapKeyVal( 0 , 0   );
    m.mCL_Subso.AddLinearMapKeyVal( 30, 1.8f );
    m.mCL_Subso.AddLinearMapKeyVal( 35, 1.9f );
    m.mCL_Subso.AddLinearMapKeyVal( 40, 1.8f );
    m.mCL_Subso.AddLinearMapKeyVal( 50, 1.2f );
    m.mCL_Subso.AddLinearMapKeyVal( 60, 0    ); // stall

    // Mach 1.4
    m.mCL_Super.AddLinearMapKeyVal( 0 , 0   );
    m.mCL_Super.AddLinearMapKeyVal( 16, 0.8f );
    m.mCL_Super.AddLinearMapKeyVal( 50, 0.8f );
    m.mCL_Super.AddLinearMapKeyVal( 60, 0    ); // negligible ?

    // drag
    // see: https://en.wikipedia.org/wiki/Drag_coefficient
    m.mCD_Subso.AddLinearMapKeyVal(  0 , 0.044f ); // F-4 (ssonic)
    m.mCD_Subso.AddLinearMapKeyVal(  90, 1.05f );  // cube (ssonic)
#else
    // see: http://www.kdu.ac.lk/proceedings/irc2015/2015/eng-012.pdf
    // Mach 0.6
#ifdef TEMP_NICE_F16_CL_AOA0
    m.mCL_Subso.AddLinearMapKeyVal( 0 , -0.05f );
#else
    m.mCL_Subso.AddLinearMapKeyVal( 0 , -0.2f );
#endif
    m.mCL_Subso.AddLinearMapKeyVal( 10, 0.55f );
    m.mCL_Subso.AddLinearMapKeyVal( 20, 1.15f );
    m.mCL_Subso.AddLinearMapKeyVal( 30, 1.55f );
    m.mCL_Subso.AddLinearMapKeyVal( 40, 1.60f );
    m.mCL_Subso.AddLinearMapKeyVal( 60, 0    ); // stall

    // Mach 1.2
#ifdef TEMP_NICE_F16_CL_AOA0
    m.mCL_Super.AddLinearMapKeyVal( 0 , -0.05f );
#else
    m.mCL_Super.AddLinearMapKeyVal( 0 , -0.25f );
#endif
    m.mCL_Super.AddLinearMapKeyVal( 10, 0.30f );
    m.mCL_Super.AddLinearMapKeyVal( 20, 0.80f );
    m.mCL_Super.AddLinearMapKeyVal( 30, 1.10f );
    m.mCL_Super.AddLinearMapKeyVal( 40, 1.25f );
    m.mCL_Super.AddLinearMapKeyVal( 60, 0    ); // negligible ?

    m.mCD_Subso.AddLinearMapKeyVal(  0 , 0.040f );
    m.mCD_Subso.AddLinearMapKeyVal(  10, 0.050f );
    m.mCD_Subso.AddLinearMapKeyVal(  20, 0.300f );
    m.mCD_Subso.AddLinearMapKeyVal(  30, 0.600f );
    m.mCD_Subso.AddLinearMapKeyVal(  40, 1.050f );
    m.mCD_Subso.AddLinearMapKeyVal(  50, 2.000f ); // closing value

    m.mCD_Super.AddLinearMapKeyVal(  0 , 0.100f );
    m.mCD_Super.AddLinearMapKeyVal(  10, 0.150f );
    m.mCD_Super.AddLinearMapKeyVal(  20, 0.450f );
    m.mCD_Super.AddLinearMapKeyVal(  30, 0.900f );
    m.mCD_Super.AddLinearMapKeyVal(  40, 1.400f );
    m.mCD_Super.AddLinearMapKeyVal(  50, 2.000f ); // closing value
#endif

    // assume we get 70% of lift when inverted
    m.mLiftCoeForNegAlpha = -0.7f;
    }

#if 0
    // see: http://www.globalsecurity.org/military/systems/aircraft/f-15-specs.htm
    m.mRefSurfaceArea = 56.0f;
#endif

    { // small missile
    auto &m = mModels[TYPE_SMALL_MISSILE];

    // NOTE: using the wetted area
    // see: http://www.f-16.net/forum/viewtopic.php?f=38&t=28234&start=60
    // http://www.f-16.net/forum/viewtopic.php?f=38&t=28234&sid=b61f53615527f000a59471c719c60141&start=60
    m.mRefSurfaceArea = 2.5f;

    // NOTE: kind of based on below
    m.mCL_Subso.AddLinearMapKeyVal( 0 , 0.0f );
    m.mCL_Subso.AddLinearMapKeyVal( 30, 0.1f );
    m.mCL_Subso.AddLinearMapKeyVal( 40, 0.1f );
    m.mCL_Subso.AddLinearMapKeyVal( 60, 0.5f );
    m.mCL_Subso.AddLinearMapKeyVal( 90, 0.0f ); // stall

    // Mach 1.4
    m.mCL_Super.AddLinearMapKeyVal( 0 , 0.0f );
    m.mCL_Super.AddLinearMapKeyVal( 30, 0.1f );
    m.mCL_Super.AddLinearMapKeyVal( 60, 0.5f );
    m.mCL_Super.AddLinearMapKeyVal( 90, 0.0f ); // ngligible ?

    // assume flighting inverted has no reduced effect on lift
    m.mLiftCoeForNegAlpha = -1.0f;

    // drag
    // see: http://www.zaretto.com/sites/zaretto.com/files/missile-aerodynamic-data/AIM120C5-Performance-Assessment-rev2.pdf
    m.mCD_Subso.AddLinearMapKeyVal(  0 , 0.004f );
    m.mCD_Subso.AddLinearMapKeyVal(  30, 0.030f );
    m.mCD_Subso.AddLinearMapKeyVal(  90, 0.300f );
    }
}

//==================================================================
static float sampleLDLinearMap(
                    const LinearMap &subsoMap,
                    const LinearMap &superMap,
                    const float negAlphaCoe,
                    float alpha,
                    float mach )
{
    const auto &useMap = (mach >= SSONIC_MACH_REF_VAL && !superMap.empty())
                            ? superMap
                            : subsoMap;

    const auto coe = alpha >= 0 ? 1.f : negAlphaCoe;

    return coe * useMap.SampleLinearMap( fabs( alpha ) );

}

//==================================================================
float LiftDrag::ModelEntry::CalcCL( float alpha, float mach ) const
{
    return sampleLDLinearMap( mCL_Subso, mCL_Super, mLiftCoeForNegAlpha, alpha, mach );
}

//==================================================================
float LiftDrag::ModelEntry::CalcCD( float alpha, float mach ) const
{
    return sampleLDLinearMap( mCD_Subso, mCD_Super, mDragCoeForNegAlpha, alpha, mach );
}

//==================================================================
float LiftDrag::ModelEntry::CalcLDFactor( float speed, float altitudeM ) const
{
    const auto rho = FMUT::CalcAirDesnity( altitudeM );

    return 0.5f * rho * (speed * speed) * mRefSurfaceArea;
}

//==================================================================
}

FM_LiftDrag.h

//==================================================================
/// FM_LiftDrag.h
///
/// Created by Davide Pasca - 2017/6/7
/// See the file "license.txt" that comes with this project for
/// copyright info.
//==================================================================

#ifndef FM_LIFTDRAG_H
#define FM_LIFTDRAG_H

#include "LinearMap.h"

//==================================================================
namespace FM
{

//==================================================================
class LiftDrag
{
public:
    enum Type
    {
        TYPE_F16,
        TYPE_SMALL_MISSILE,
        TYPE_N,
    };

    class ModelEntry
    {
        friend class LiftDrag;

    private:
        LinearMap mCL_Subso;
        LinearMap mCL_Super;

        LinearMap mCD_Subso;
        LinearMap mCD_Super;

        // coefficient for negative lift
        // ...only an approximation. Ideally we'd get actual data
        //  like for positive alpha..
        float     mLiftCoeForNegAlpha = -1;

        float     mDragCoeForNegAlpha =  1;

        float     mRefSurfaceArea = 1;

    public:
        float CalcCL( float alpha, float mach ) const;
        float CalcCD( float alpha, float mach ) const;
        float CalcLDFactor( float speed, float altitudeM ) const;
    };

private:
    ModelEntry  mModels[TYPE_N];

public:
    LiftDrag();

    const ModelEntry &GetLiftDragModel( Type type ) const
    {
        return mModels[ type ];
    }
};

//==================================================================
}

#endif