_f0 = 2*_etaC*power/(rho*v*V2);
_matchTakeoff = false;
+ _manual = false;
+ _proppitch = 0;
+ _propfeather = 0;
}
void Propeller::setTakeoff(float omega0, float power0)
float density = Atmosphere::getStdDensity(0);
_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 < 0.25f*_baseJ0) _j0 = 0.25f*_baseJ0;
- if(_j0 > 4*_baseJ0) _j0 = 4*_baseJ0;
+ 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;
-
- // The model doesn't work for propellers turning backwards.
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 = 1.0f/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 == 1.0) lambda = 0.9999f;
+ 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 = 0.5f * density * V2 * _f0 * tc;
-
- if(torque > 0) {
- torque -= thrust/gamma;
- thrust = -thrust;
- } else {
- torque = thrust/gamma;
+ 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;