YASim bugfix: ground effect did not calculate wingspan correctly;

Variable name clarification;
Add Wing::getWingArea, separate Wing::getWingSpan and Wing::getBase.

src/FDM/YASim/Airplane.cpp

@@ -471,25 +471,33 @@ void Airplane::addContactPoint(float* pos)
 
 float Airplane::compileWing(Wing* w)
 {
+    // Make sure it's initialized.  The surfaces will pop out with
+    // total drag coefficients equal to their areas, which is what we
+    // want.
+    w->compile();
+
     // The tip of the wing is a contact point
     float tip[3];
+    // need compile() before getTip()!
     w->getTip(tip);
     addContactPoint(tip);
     if(w->isMirrored()) {
         tip[1] *= -1;
         addContactPoint(tip);
+        tip[1] *= -1; //undo mirror
     }
     if (_wingsN != 0) {
       _wingsN->getNode("tip-x", true)->setFloatValue(tip[0]);
       _wingsN->getNode("tip-y", true)->setFloatValue(tip[1]);
       _wingsN->getNode("tip-z", true)->setFloatValue(tip[2]);
+      w->getBase(tip);
+      _wingsN->getNode("base-x", true)->setFloatValue(tip[0]);
+      _wingsN->getNode("base-y", true)->setFloatValue(tip[1]);
+      _wingsN->getNode("base-z", true)->setFloatValue(tip[2]);
+      _wingsN->getNode("wingspan", true)->setFloatValue(w->getWingSpan());
+      _wingsN->getNode("wingarea", true)->setFloatValue(w->getWingArea());
     }
 
-    // Make sure it's initialized.  The surfaces will pop out with
-    // total drag coefficients equal to their areas, which is what we
-    // want.
-    w->compile();
-
     float wgt = 0;
     float dragSum = 0;
     for(int i=0; i<w->numSurfaces(); i++) {
@@ -764,7 +772,9 @@ void Airplane::compile()
     if(_wing) {
         float gepos[3];
         float gespan = 0;
-        gespan = _wing->getGroundEffect(gepos);
+        gespan = _wing->getWingSpan();
+	_wing->getBase(gepos);
+        // where does the hard coded factor 0.15 come from?
         _model.setGroundEffect(gepos, gespan, 0.15f);
     }
 

src/FDM/YASim/Model.cpp

@@ -66,9 +66,9 @@ Model::Model()
     _hook = 0;
     _launchbar = 0;
 
-    _groundEffectSpan = 0;
+    _wingSpan = 0;
     _groundEffect = 0;
-    for(i=0; i<3; i++) _wingCenter[i] = 0;
+    for(i=0; i<3; i++) _geRefPoint[i] = 0;
 
     _global_ground[0] = 0; _global_ground[1] = 0; _global_ground[2] = 1;
     _global_ground[3] = -100000;
@@ -289,8 +289,8 @@ Ground* Model::getGroundCallback(void)
 
 void Model::setGroundEffect(float* pos, float span, float mul)
 {
-    Math::set3(pos, _wingCenter);
-    _groundEffectSpan = span;
+    Math::set3(pos, _geRefPoint);
+    _wingSpan = span;
     _groundEffect = mul;
 }
 
@@ -470,16 +470,19 @@ void Model::calcForces(State* s)
     // Account for ground effect by multiplying the vertical force
     // component by an amount linear with the fraction of the wingspan
     // above the ground.
-    if ((_groundEffectSpan != 0) && (_groundEffect != 0 ))
+    if ((_wingSpan != 0) && (_groundEffect != 0 ))
     {
-        float dist = ground[3] - Math::dot3(ground, _wingCenter);
-        if(dist > 0 && dist < _groundEffectSpan) {
-        float fz = Math::dot3(faero, ground);
-            fz *= (_groundEffectSpan - dist) / _groundEffectSpan;
-            fz *= _groundEffect;
-        Math::mul3(fz, ground, faero);
-        _body.addForce(faero);
-        }
+      // distance between ground and wing ref. point
+      float dist = ground[3] - Math::dot3(ground, _geRefPoint); 
+      float fz = 0;
+      float geForce[3];
+      if(dist > 0 && dist < _wingSpan) {
+        fz = Math::dot3(faero, ground);
+        fz *= (_wingSpan - dist) / _wingSpan;
+        fz *= _groundEffect;
+        Math::mul3(fz, ground, geForce);
+        _body.addForce(geForce);
+      }      
     }
     
     // Convert the velocity and rotation vectors to local coordinates

src/FDM/YASim/Model.hpp

@@ -96,9 +96,9 @@ private:
     Launchbar* _launchbar;
     Vector _hitches;
 
-    float _groundEffectSpan;
+    float _wingSpan;
     float _groundEffect;
-    float _wingCenter[3];
+    float _geRefPoint[3];
 
     Ground* _ground_cb;
     double _global_ground[4];

src/FDM/YASim/Wing.cpp

@@ -1,4 +1,3 @@
-#include "Math.hpp"
 #include "Surface.hpp"
 #include "Wing.hpp"
 
@@ -228,30 +227,6 @@ void Wing::setSlatPos(float val)
 	((Surface*)_slatSurfs.get(i))->setSlatPos(val);
 }
 
-float Wing::getGroundEffect(float* posOut)
-{
-    int i;
-    for(i=0; i<3; i++) posOut[i] = _base[i];
-    float span = _length * Math::cos(_sweep) * Math::cos(_dihedral);
-    span = 2*(span + Math::abs(_base[2]));
-    return span;
-}
-
-void Wing::getTip(float* tip)
-{
-    tip[0] = -Math::tan(_sweep);
-    tip[1] = Math::cos(_dihedral);
-    tip[2] = Math::sin(_dihedral);
-    Math::unit3(tip, tip);
-    Math::mul3(_length, tip, tip);
-    Math::add3(_base, tip, tip);
-}
-
-bool Wing::isMirrored()
-{
-    return _mirror;
-}
-
 void Wing::compile()
 {
     // Have we already been compiled?
@@ -306,12 +281,13 @@ void Wing::compile()
     Math::unit3(left, left);
 
     // Calculate coordinates for the root and tip of the wing
-    float root[3], tip[3];
+    float root[3];
     Math::set3(_base, root);
-    Math::set3(left, tip);
-    Math::mul3(_length, tip, tip);
-    Math::add3(root, tip, tip);
-
+    Math::set3(left, _tip);
+    Math::mul3(_length, _tip, _tip);
+    Math::add3(root, _tip, _tip);
+    _wingspan = Math::abs(2*_tip[1]);
+    
     // The wing's Y axis will be the "left" vector.  The Z axis will
     // be perpendicular to this and the local (!) X axis, because we
     // want motion along the local X axis to be zero AoA (i.e. in the
@@ -363,7 +339,7 @@ void Wing::compile()
         for(j=0; j<nSegs; j++) {
             float frac = start + (j+0.5f) * (end-start)/nSegs;
             float pos[3];
-            interp(root, tip, frac, pos);
+            interp(root, _tip, frac, pos);
 
             float chord = _chord * (1 - (1-_taper)*frac);
 

src/FDM/YASim/Wing.hpp

@@ -3,6 +3,7 @@
 
 #include "Vector.hpp"
 #include "Version.hpp"
+#include "Math.hpp"
 
 namespace yasim {
 
@@ -24,7 +25,13 @@ public:
     void setTaper(float taper);       // fraction, 0-1
     void setSweep(float sweep);       // radians
     void setDihedral(float dihedral); // radians, positive is "up"
-
+    void getBase(float* base) { Math::set3(_base, base); };
+    float getLength() { return _length; };
+    float getChord() { return _chord; };
+    float getTaper() { return _taper; };
+    float getSweep() { return _sweep; };
+    float getDihedral() { return _dihedral; };
+    
     void setStall(float aoa);
     void setStallWidth(float angle);
     void setStallPeak(float fraction);
@@ -48,13 +55,11 @@ public:
 
     // Compile the thing into a bunch of Surface objects
     void compile();
-
-    void getTip(float* tip);
-
-    bool isMirrored();
-
-    // Ground effect information
-    float getGroundEffect(float* posOut);
+    void getTip(float* tip) { Math::set3(_tip, tip);};
+    bool isMirrored() { return _mirror; };
+    // Used for ground effect 
+    float getWingSpan() { return _wingspan; };
+    float getWingArea() {return 0.5f*_wingspan*_chord*(1+_taper); };
     
     // Query the list of Surface objects
     int numSurfaces();
@@ -92,6 +97,10 @@ private:
     float _taper;
     float _sweep;
     float _dihedral;
+    
+    // calculated from above
+    float _tip[3];
+    float _wingspan;
 
     float _stall;
     float _stallWidth;