How to create a realistic missile-vessel

Topper · Apr 11, 2008

Hi,

I am not an expert in aerodynamic.
i wan't to create a vessel for my missile add on witch can be fly stable with speeds near 1400 m/s near see level. At this time my vessel begin to shake around at speeds more than 1000m/s.
My question is what respect by using "CreateAirfoil3" and inside the "VLiftCoeff" / "HLiftCoeff" function to get a "near realistic flight model"?
reg.
Topper

My modified vessel code from the shuttlePB (i know i have cheated a bit...):

Code:

// ==============================================================
//                 ORBITER MODULE: ShuttlePB
//                  Part of the ORBITER SDK
//          Copyright (C) 2002-2004 Martin Schweiger
//                   All rights reserved
//
// ShuttlePB.cpp
// Control module for ShuttlePB vessel class
//
// Notes:
// This is an example for a "minimal" vessel implementation which
// only overloads the clbkSetClassCaps method to define vessel
// capabilities and otherwise uses the default VESSEL class
// behaviour.
// ==============================================================

//#define STRICT
#include "AAMissile.h"
#define ORBITER_MODULE

// ==============================================================
// Some vessel parameters
// ==============================================================
const double PB_FUELMASS = 125.0;
const double PB_ISP = 980;
const double PB_MAXMAINTH = 2.0e4;
//const double PB_MAXHOVERTH = 1.5e4;
const double PB_MAXRCSTH = 50;

// Calculate lift coefficient [Cl] as a function of aoa (angle of attack) over -Pi ... Pi
// Implemented here as a piecewise linear function


void VLiftCoeff (VESSEL *v, double aoa, double M, double Re, void *context, double *cl, double *cm, double *cd)
{
    int i;
    const int nabsc = 9;
    static const double AOA[nabsc] = {-180*RAD,-60*RAD,-30*RAD, -2*RAD, 8*RAD,20*RAD,25*RAD,60*RAD,180*RAD};
    static const double CL[nabsc]  = {       0,      0,   -0.4,      0,    0.04,     1,   0.8,     0,      0};
    static const double CM[nabsc]  = {       0,      0,  0.014, 0.0039, -0.006,-0.008,-0.010,     0,      0};
    for (i = 0; i < nabsc-1 && AOA[i+1] < aoa; i++);
    double f = (aoa-AOA[i]) / (AOA[i+1]-AOA[i]);
    *cl = CL[i] + (CL[i+1]-CL[i]) * f;  // aoa-dependent lift coefficient
    *cm = CM[i] + (CM[i+1]-CM[i]) * f;  // aoa-dependent moment coefficient
    double saoa = sin(aoa);
    double pd = 0.001 + 0.01*saoa*saoa;  // profile drag
    *cd = pd + (oapiGetInducedDrag (*cl, 1.1, 0.9) + oapiGetWaveDrag (M, 0.75, 1.0, 1.1, 0.04))/30;
    // profile drag + (lift-)induced drag + transonic/supersonic wave (compressibility) drag
}
// 2. horizontal lift component (vertical stabilisers and body)

void HLiftCoeff (VESSEL *v, double beta, double M, double Re, void *context, double *cl, double *cm, double *cd)
{
    int i;
    const int nabsc = 8;
    static const double BETA[nabsc] = {-180*RAD,-135*RAD,-90*RAD,-45*RAD,45*RAD,90*RAD,135*RAD,180*RAD};
    static const double CL[nabsc]   = {       0,    +0.3,      0,   -0.3,  +0.3,     0,   -0.3,      0};
    for (i = 0; i < nabsc-1 && BETA[i+1] < beta; i++);
    *cl = CL[i] + (CL[i+1]-CL[i]) * (beta-BETA[i]) / (BETA[i+1]-BETA[i]);
    *cm = 0.0;
    *cd =  0.001 + (oapiGetInducedDrag (*cl, 1.1, 0.9) + oapiGetWaveDrag (M, 0.75, 1.0, 1.1, 0.04))/30;
}

// ==============================================================
// Shuttle-PB class interface
// ==============================================================



// ==============================================================
// Overloaded callback functions
// ==============================================================

// --------------------------------------------------------------
// Set the capabilities of the vessel class
// --------------------------------------------------------------

void AIM120::clbkSetClassCaps (FILEHANDLE cfg)
{
    
    anim_x = CreateAnimation (0);

    THRUSTER_HANDLE th_main;
    SetSize (10);
    SetEmptyMass (35.0);
//make wings
    CreateAirfoil3 (LIFT_VERTICAL, _V(0,0,-2.8), VLiftCoeff, 0, 1, 2.6, 1.2);
    //CreateAirfoil3 (LIFT_VERTICAL, _V(0,0, 4), VLiftCoeff, 0, 1, 0.5, 1.6);
    // wing and body lift+drag components

    CreateAirfoil3 (LIFT_HORIZONTAL, _V(0,0,-2.8), HLiftCoeff, 0, 1, 2.6, 1.2);
    //CreateAirfoil3 (LIFT_HORIZONTAL, _V(0,0, 4), HLiftCoeff, 0, 1, 0.5, 1.6);
    // vertical stabiliser and body lift and drag components

    CreateControlSurface (AIRCTRL_ELEVATOR,     0.4, 2.5, _V(   0,0,-7.2), AIRCTRL_AXIS_XPOS, anim_x);
    CreateControlSurface (AIRCTRL_RUDDER,       0.4, 2.5, _V(   0,0,-7.2), AIRCTRL_AXIS_YPOS, anim_x);
    CreateControlSurface2 (AIRCTRL_AILERON,        0.4, 2.5, _V( 7.5,0,-7.2), AIRCTRL_AXIS_XPOS, anim_x);
    CreateControlSurface2 (AIRCTRL_AILERON,        0.4, 2.5, _V(-7.5,0,-7.2), AIRCTRL_AXIS_XNEG, anim_x);
    CreateControlSurface (AIRCTRL_ELEVATORTRIM, 0.4, 2.5, _V(   0,0,-7.2), AIRCTRL_AXIS_XPOS, anim_x);


    PROPELLANT_HANDLE hpr = CreatePropellantResource (PB_FUELMASS);


    th_main = CreateThruster (_V(0,0,-4.35), _V(0,0,1), PB_MAXMAINTH, hpr, PB_ISP);
    CreateThrusterGroup (&th_main, 1, THGROUP_MAIN);

    // visual specs
/*
    PARTICLESTREAMSPEC contrail_main = {
        0, 5.0, 16, 200, 0.15, 1.0, 5, 3.0, PARTICLESTREAMSPEC::DIFFUSE,
        PARTICLESTREAMSPEC::LVL_PSQRT, 0, 2,
        PARTICLESTREAMSPEC::ATM_PLOG, 1e-4, 1
    };

    PARTICLESTREAMSPEC exhaust_main = {
        0, 2.0, 20, 200, 0.05, 0.1, 8, 1.0, PARTICLESTREAMSPEC::EMISSIVE,
        PARTICLESTREAMSPEC::LVL_SQRT, 0, 1,
        PARTICLESTREAMSPEC::ATM_PLOG, 1e-5, 0.1
    };
*/
    AddExhaust (th_main, 5, 0.25, _V(0,0,-1.82), _V(0,0,-1));
    //AddExhaustStream (th_main, _V(0,0.1,-10), &contrail_main);
    //AddExhaustStream (th_main, _V(0,0.1,-5), &exhaust_main);

    //SetTouchdownPoints (_V(0,-1.5,-2.6), _V(-0.2,1.5,-2.6), _V(0.2,0,-1.6));
    //AG : SetTouchdownPoints (_V(0,-3.5,2), _V(-1,-1.0,-1.5), _V(1,-1.0,-1.5));
    SetTouchdownPoints (_V(0,-1,2), _V(-1,-1.0,-1.5), _V(1,-1.0,-1.5));
    
    AddMesh ("AAMissile");
    SetReentryTexture(NULL);                            
}

// ==============================================================
// API callback interface
// ==============================================================

// --------------------------------------------------------------
// Vessel initialisation
// --------------------------------------------------------------

DLLCLBK VESSEL *ovcInit (OBJHANDLE hvessel, int flightmodel)
{
    return new AIM120 (hvessel, flightmodel);
}

// --------------------------------------------------------------
// Vessel cleanup
// --------------------------------------------------------------
DLLCLBK void ovcExit (VESSEL *vessel)
{
    if (vessel) delete (AIM120*)vessel;
}


void AIM120::clbkDrawHUD (int mode, const HUDPAINTSPEC *hps, HDC hDC)
{
        // draw the default HUD
    VESSEL2::clbkDrawHUD (mode, hps, hDC);
    
    int cx = hps->CX;
    int cy = hps->CY;
    int RADIUS = 500*(cx/cy);
    int CenterX = cx;
    int CenterY = cy;
    Ellipse (hDC, 
        CenterX - RADIUS, 
        CenterY + RADIUS,
        CenterX + RADIUS,
        CenterY - RADIUS);
}

double AIM120::GetVesselDistance2(OBJHANDLE hVesselFrom, VESSEL* VesselTo)
{
    VECTOR3 v3;
    VesselTo->GetRelativePos(hVesselFrom,v3);
    double TotalDistance = sqrt((v3.x * v3.x) + (v3.y * v3.y) + (v3.z * v3.z));
    return TotalDistance;
}


void AIM120::clbkPostStep (double simt, double simdt, double mjd)
{
    //walpha.wMain();
}

Urwumpe · Apr 11, 2008

The instability comes when you have very strong gradients in the lift function. Make the lift function a bit less extreme and demand higher AOAs for maximum L/D.

mikey451 · Apr 11, 2008

And the moment function...

Eagle · Apr 11, 2008

mikey451 said:
And the moment function...

Yeah, that's an easy thing to overlook. If you increase the vessel's moment of inertia it will resist its airfoils more. Too much rotational inertia and it will oscillate. This is known as inertia coupling: http://en.wikipedia.org/wiki/Inertia_coupling

sts-107 · Jun 1, 2008

Hi Topper,

I hope those pages will assist you http://www.megaupload.com/?d=RN5L847V
As well any plans in future to implement TVC steering methods (for high altitudes)?

Best regards,
Alex.

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How to create a realistic missile-vessel

Topper

Addon Developer

Urwumpe

Not funny anymore

mikey451

Addon Developer

Eagle

The Amazing Flying Tuna Can

sts-107

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