7228024ed5
if desired) in the stall. This allows for fairly docile stalls when desired, as on trainers (you also need to limit the elevator lift).
306 lines
7.2 KiB
C++
306 lines
7.2 KiB
C++
#include "Math.hpp"
|
|
#include "Surface.hpp"
|
|
namespace yasim {
|
|
|
|
Surface::Surface()
|
|
{
|
|
// Start in a "sane" mode, so unset stuff doesn't freak us out
|
|
_c0 = 1;
|
|
_cx = _cy = _cz = 1;
|
|
_cz0 = 0;
|
|
_peaks[0] = _peaks[1] = 1;
|
|
int i;
|
|
for(i=0; i<4; i++) {
|
|
_stalls[i] = 0;
|
|
_widths[i] = 0.01; // half a degree
|
|
}
|
|
_orient[0] = 1; _orient[1] = 0; _orient[2] = 0;
|
|
_orient[3] = 0; _orient[4] = 1; _orient[5] = 0;
|
|
_orient[6] = 0; _orient[7] = 0; _orient[8] = 1;
|
|
|
|
_chord = 0;
|
|
_incidence = 0;
|
|
_twist = 0;
|
|
_slatPos = _spoilerPos = _flapPos = 0;
|
|
_slatDrag = _spoilerDrag = _flapDrag = 1;
|
|
|
|
_flapLift = 0;
|
|
_slatAlpha = 0;
|
|
_spoilerLift = 1;
|
|
_inducedDrag = 1;
|
|
}
|
|
|
|
void Surface::setPosition(float* p)
|
|
{
|
|
int i;
|
|
for(i=0; i<3; i++) _pos[i] = p[i];
|
|
}
|
|
|
|
void Surface::getPosition(float* out)
|
|
{
|
|
int i;
|
|
for(i=0; i<3; i++) out[i] = _pos[i];
|
|
}
|
|
|
|
void Surface::setChord(float chord)
|
|
{
|
|
_chord = chord;
|
|
}
|
|
|
|
void Surface::setTotalDrag(float c0)
|
|
{
|
|
_c0 = c0;
|
|
}
|
|
|
|
float Surface::getTotalDrag()
|
|
{
|
|
return _c0;
|
|
}
|
|
|
|
void Surface::setXDrag(float cx)
|
|
{
|
|
_cx = cx;
|
|
}
|
|
|
|
void Surface::setYDrag(float cy)
|
|
{
|
|
_cy = cy;
|
|
}
|
|
|
|
void Surface::setZDrag(float cz)
|
|
{
|
|
_cz = cz;
|
|
}
|
|
|
|
void Surface::setBaseZDrag(float cz0)
|
|
{
|
|
_cz0 = cz0;
|
|
}
|
|
|
|
void Surface::setStallPeak(int i, float peak)
|
|
{
|
|
_peaks[i] = peak;
|
|
}
|
|
|
|
void Surface::setStall(int i, float alpha)
|
|
{
|
|
_stalls[i] = alpha;
|
|
}
|
|
|
|
void Surface::setStallWidth(int i, float width)
|
|
{
|
|
_widths[i] = width;
|
|
}
|
|
|
|
void Surface::setOrientation(float* o)
|
|
{
|
|
int i;
|
|
for(i=0; i<9; i++)
|
|
_orient[i] = o[i];
|
|
}
|
|
|
|
void Surface::setIncidence(float angle)
|
|
{
|
|
_incidence = angle;
|
|
}
|
|
|
|
void Surface::setTwist(float angle)
|
|
{
|
|
_twist = angle;
|
|
}
|
|
|
|
void Surface::setSlatParams(float stallDelta, float dragPenalty)
|
|
{
|
|
_slatAlpha = stallDelta;
|
|
_slatDrag = dragPenalty;
|
|
}
|
|
|
|
void Surface::setFlapParams(float liftAdd, float dragPenalty)
|
|
{
|
|
_flapLift = liftAdd;
|
|
_flapDrag = dragPenalty;
|
|
}
|
|
|
|
void Surface::setSpoilerParams(float liftPenalty, float dragPenalty)
|
|
{
|
|
_spoilerLift = liftPenalty;
|
|
_spoilerDrag = dragPenalty;
|
|
}
|
|
|
|
void Surface::setFlap(float pos)
|
|
{
|
|
_flapPos = pos;
|
|
}
|
|
|
|
void Surface::setSlat(float pos)
|
|
{
|
|
_slatPos = pos;
|
|
}
|
|
|
|
void Surface::setSpoiler(float pos)
|
|
{
|
|
_spoilerPos = pos;
|
|
}
|
|
|
|
// Calculate the aerodynamic force given a wind vector v (in the
|
|
// aircraft's "local" coordinates) and an air density rho. Returns a
|
|
// torque about the Y axis, too.
|
|
void Surface::calcForce(float* v, float rho, float* out, float* torque)
|
|
{
|
|
// Split v into magnitude and direction:
|
|
float vel = Math::mag3(v);
|
|
|
|
// Handle the blowup condition. Zero velocity means zero force by
|
|
// definition.
|
|
if(vel == 0) {
|
|
int i;
|
|
for(i=0; i<3; i++) out[i] = torque[i] = 0;
|
|
return;
|
|
}
|
|
|
|
Math::mul3(1/vel, v, out);
|
|
|
|
// Convert to the surface's coordinates
|
|
Math::vmul33(_orient, out, out);
|
|
|
|
// "Rotate" by the incidence angle. Assume small angles, so we
|
|
// need to diddle only the Z component, X is relatively unchanged
|
|
// by small rotations.
|
|
float incidence = _incidence + _twist;
|
|
out[2] += incidence * out[0]; // z' = z + incidence * x
|
|
|
|
// Hold onto the local wind vector so we can multiply the induced
|
|
// drag at the end.
|
|
float lwind[3];
|
|
Math::set3(out, lwind);
|
|
|
|
// Diddle the Z force according to our configuration
|
|
float stallMul = stallFunc(out);
|
|
stallMul *= 1 + _spoilerPos * (_spoilerLift - 1);
|
|
float stallLift = (stallMul - 1) * _cz * out[2];
|
|
float flaplift = flapLift(out[2]);
|
|
|
|
out[2] *= _cz; // scaling factor
|
|
out[2] += _cz*_cz0; // zero-alpha lift
|
|
out[2] += stallLift;
|
|
out[2] += flaplift;
|
|
|
|
// Airfoil lift (pre-stall and zero-alpha) torques "up" (negative
|
|
// torque) around the Y axis, while flap lift pushes down. Both
|
|
// forces are considered to act at one third chord from the
|
|
// edge. Convert to local (i.e. airplane) coordiantes and store
|
|
// into "torque".
|
|
torque[0] = 0;
|
|
torque[1] = 0.1667f * _chord * (flaplift - (_cz*_cz0 + stallLift));
|
|
torque[2] = 0;
|
|
Math::tmul33(_orient, torque, torque);
|
|
|
|
// The X (drag) force gets diddled for control deflection
|
|
out[0] = controlDrag(out[2], _cx * out[0]);
|
|
|
|
// Add in any specific Y (side force) coefficient.
|
|
out[1] *= _cy;
|
|
|
|
// Diddle the induced drag
|
|
float IDMUL = 0.5;
|
|
Math::mul3(-1*_inducedDrag*out[2]*lwind[2], lwind, lwind);
|
|
Math::add3(lwind, out, out);
|
|
|
|
// Reverse the incidence rotation to get back to surface
|
|
// coordinates.
|
|
out[2] -= incidence * out[0];
|
|
|
|
// Convert back to external coordinates
|
|
Math::tmul33(_orient, out, out);
|
|
|
|
// Add in the units to make a real force:
|
|
float scale = 0.5f*rho*vel*vel*_c0;
|
|
Math::mul3(scale, out, out);
|
|
Math::mul3(scale, torque, torque);
|
|
}
|
|
|
|
// Returns a multiplier for the "plain" force equations that
|
|
// approximates an airfoil's lift/stall curve.
|
|
float Surface::stallFunc(float* v)
|
|
{
|
|
// Sanity check to treat FPU psychopathology
|
|
if(v[0] == 0) return 1;
|
|
|
|
float alpha = Math::abs(v[2]/v[0]);
|
|
|
|
// Wacky use of indexing, see setStall*() methods.
|
|
int fwdBak = v[0] > 0; // set if this is "backward motion"
|
|
int posNeg = v[2] < 0; // set if the lift is toward -z
|
|
int i = (fwdBak<<1) | posNeg;
|
|
|
|
float stallAlpha = _stalls[i];
|
|
if(stallAlpha == 0)
|
|
return 1;
|
|
|
|
if(i == 0)
|
|
stallAlpha += _slatAlpha;
|
|
|
|
// Beyond the stall
|
|
if(alpha > stallAlpha+_widths[i])
|
|
return 1;
|
|
|
|
// (note mask: we want to use the "positive" stall angle here)
|
|
float scale = 0.5f*_peaks[fwdBak]/_stalls[i&2];
|
|
|
|
// Before the stall
|
|
if(alpha <= stallAlpha)
|
|
return scale;
|
|
|
|
// Inside the stall. Compute a cubic interpolation between the
|
|
// pre-stall "scale" value and the post-stall unity.
|
|
float frac = (alpha - stallAlpha) / _widths[i];
|
|
frac = frac*frac*(3-2*frac);
|
|
|
|
return scale*(1-frac) + frac;
|
|
}
|
|
|
|
// Similar to the above -- interpolates out the flap lift past the
|
|
// stall alpha
|
|
float Surface::flapLift(float alpha)
|
|
{
|
|
float flapLift = _cz * _flapPos * (_flapLift-1);
|
|
|
|
if(alpha < 0) alpha = -alpha;
|
|
if(alpha < _stalls[0])
|
|
return flapLift;
|
|
else if(alpha > _stalls[0] + _widths[0])
|
|
return 1;
|
|
|
|
float frac = (alpha - _stalls[0]) / _widths[0];
|
|
frac = frac*frac*(3-2*frac);
|
|
return flapLift * (1-frac) + frac;
|
|
}
|
|
|
|
float Surface::controlDrag(float lift, float drag)
|
|
{
|
|
// Negative flap deflections don't affect drag until their lift
|
|
// multiplier exceeds the "camber" (cz0) of the surface. Use a
|
|
// synthesized "fp" number instead of the actual flap position.
|
|
float fp = _flapPos;
|
|
if(fp < 0) {
|
|
fp = -fp;
|
|
fp -= _cz0/(_flapLift-1);
|
|
if(fp < 0) fp = 0;
|
|
}
|
|
|
|
// Calculate an "effective" drag -- this is the drag that would
|
|
// have been produced by an unflapped surface at the same lift.
|
|
float flapDragAoA = (_flapLift - 1 - _cz0) * _stalls[0];
|
|
float fd = Math::abs(lift * flapDragAoA * fp);
|
|
if(drag < 0) fd = -fd;
|
|
drag += fd;
|
|
|
|
// Now multiply by the various control factors
|
|
drag *= 1 + fp * (_flapDrag - 1);
|
|
drag *= 1 + _spoilerPos * (_spoilerDrag - 1);
|
|
drag *= 1 + _slatPos * (_slatDrag - 1);
|
|
|
|
return drag;
|
|
}
|
|
|
|
}; // namespace yasim
|