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[flightgear.git] / src / FDM / YASim / Propeller.cpp

diff --git a/src/FDM/YASim/Propeller.cpp b/src/FDM/YASim/Propeller.cpp
index 9e6245120ae6cb075e28e929dbfa33f5a0b5f982..af19e705088467c79f54d15a7c72d3797f10562d 100644 (file)
--- a/src/FDM/YASim/Propeller.cpp
+++ b/src/FDM/YASim/Propeller.cpp
@@ -10,18 +10,21 @@ Propeller::Propeller(float radius, float v, float omega,
 {
     // Initialize numeric constants:
     _lambdaPeak = Math::pow(5.0, -1.0/4.0);
-    _beta = 1.0/(Math::pow(5.0, -1.0/4.0) - Math::pow(5.0, -5.0/4.0));
+    _beta = 1.0f/(Math::pow(5.0f, -1.0f/4.0f) - Math::pow(5.0f, -5.0f/4.0f));
 
     _r = radius;
-    _etaC = 0.85; // make this settable?
+    _etaC = 0.85f; // make this settable?
 
-    _J0 = v/(omega*_lambdaPeak);
-    _baseJ0 = _J0;
+    _j0 = v/(omega*_lambdaPeak);
+    _baseJ0 = _j0;
 
     float V2 = v*v + (_r*omega)*(_r*omega);
-    _F0 = 2*_etaC*power/(rho*v*V2);
+    _f0 = 2*_etaC*power/(rho*v*V2);
 
     _matchTakeoff = false;
+    _manual = false;
+    _proppitch = 0;
+    _propfeather = 0;
 }
 
 void Propeller::setTakeoff(float omega0, float power0)
@@ -29,63 +32,87 @@ void Propeller::setTakeoff(float omega0, float power0)
     // Takeoff thrust coefficient at lambda==0
     _matchTakeoff = true;
     float V2 = _r*omega0 * _r*omega0;
-    float gamma = _etaC * _beta / _J0;
+    float gamma = _etaC * _beta / _j0;
     float torque = power0 / omega0;
     float density = Atmosphere::getStdDensity(0);
-    _tc0 = (torque * gamma) / (0.5 * density * V2 * _F0);
+    _tc0 = (torque * gamma) / (0.5f * density * V2 * _f0);
+}
+
+void Propeller::setStops(float fine_stop, float coarse_stop)
+{
+    _fine_stop = fine_stop;
+    _coarse_stop = coarse_stop;
 }
     
 void Propeller::modPitch(float mod)
 {
-    _J0 *= mod;
-    if(_J0 < 0.25*_baseJ0) _J0 = 0.25*_baseJ0;
-    if(_J0 > 4*_baseJ0)    _J0 = 4*_baseJ0;
+    _j0 *= mod;
+    if(_j0 < _fine_stop*_baseJ0) _j0 = _fine_stop*_baseJ0;
+    if(_j0 > _coarse_stop*_baseJ0)     _j0 = _coarse_stop*_baseJ0;
+}
+
+void Propeller::setManualPitch()
+{
+    _manual = true;
+}
+
+void Propeller::setPropPitch(float proppitch)
+{
+    // makes only positive range of axis effective.
+    _proppitch = Math::clamp(proppitch, 0, 1);
 }
 
+void Propeller::setPropFeather(int state)
+{
+    // 0 = normal, 1 = feathered
+    _propfeather = (state != 0);
+}
 
 void Propeller::calc(float density, float v, float omega,
                     float* thrustOut, float* torqueOut)
 {
+    // For manual pitch, exponentially modulate the J0 value between
+    // 0.25 and 4.  A prop pitch of 0.5 results in no change from the
+    // base value.
+    // TODO: integrate with _fine_stop and _coarse_stop variables
+    if (_manual) 
+        _j0 = _baseJ0 * Math::pow(2, 2 - 4*_proppitch);
+    
     float tipspd = _r*omega;
     float V2 = v*v + tipspd*tipspd;
 
-    // Clamp v (forward velocity) to zero, now that we've used it to
-    // calculate V (propeller "speed")
+    // Sanify
     if(v < 0) v = 0;
+    if(omega < 0.001) omega = 0.001;
 
-    float J = v/omega;
-    float lambda = J/_J0;
+    float J = v/omega;    // Advance ratio
+    float lambda = J/_j0; // Unitless scalar advance ratio
 
-    float torque = 0;
-    if(lambda > 1) {
-       lambda = 1.0/lambda;
-       torque = (density*V2*_F0*_J0)/(4*_etaC*_beta*(1-_lambdaPeak));
-    }
+    // There's an undefined point at lambda == 1.
+    if(lambda == 1.0f) lambda = 0.9999f;
 
-    // There's an undefined point at 1.  Just offset by a tiny bit to
-    // fix (note: the discontinuity is at EXACTLY one, this is about
-    // the only time in history you'll see me use == on a floating
-    // point number!)
-    if(lambda == 1) lambda = 0.9999;
+    float l4 = lambda*lambda; l4 = l4*l4;   // lambda^4
+    float gamma = (_etaC*_beta/_j0)*(1-l4); // thrust/torque ratio
 
-    // Calculate lambda^4
-    float l4 = lambda*lambda; l4 = l4*l4;
-
-    // thrust/torque ratio
-    float gamma = (_etaC*_beta/_J0)*(1-l4);
-
-    // Compute a thrust, clamp to takeoff thrust to prevend huge
-    // numbers at slow speeds.
+    // Compute a thrust coefficient, with clamping at very low
+    // lambdas (fast propeller / slow aircraft).
     float tc = (1 - lambda) / (1 - _lambdaPeak);
     if(_matchTakeoff && tc > _tc0) tc = _tc0;
 
-    float thrust = 0.5 * density * V2 * _F0 * tc;
-
-    if(torque > 0) {
-       torque -= thrust/gamma;
-       thrust = -thrust;
-    } else {
-       torque = thrust/gamma;
+    float thrust = 0.5f * density * V2 * _f0 * tc;
+    float torque = thrust/gamma;
+    if(lambda > 1) {
+        // This is the negative thrust / windmilling regime.  Throw
+        // out the efficiency graph approach and instead simply
+        // extrapolate the existing linear thrust coefficient and a
+        // torque coefficient that crosses the axis at a preset
+        // windmilling speed.  The tau0 value is an analytically
+        // calculated (i.e. don't mess with it) value for a torque
+        // coefficient at lamda==1.
+        float tau0 = (0.25f * _j0) / (_etaC * _beta * (1 - _lambdaPeak));
+        float lambdaWM = 1.2f; // lambda of zero torque (windmilling)
+        torque = tau0 - tau0 * (lambda - 1) / (lambdaWM - 1);
+        torque *= 0.5f * density * V2 * _f0;
     }
 
     *thrustOut = thrust;