namespace JSBSim {
-static const char *IdSrc = "$Id: FGPropeller.cpp,v 1.39 2011/10/15 13:00:57 bcoconni Exp $";
+static const char *IdSrc = "$Id: FGPropeller.cpp,v 1.44 2012/04/29 13:10:46 bcoconni Exp $";
static const char *IdHdr = ID_PROPELLER;
/*%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
double FGPropeller::Calculate(double EnginePower)
{
+ FGColumnVector3 localAeroVel = Transform().Transposed() * in.AeroUVW;
double omega, PowerAvailable;
- double Vel = in.AeroUVW(eU);
+ double Vel = localAeroVel(eU);
double rho = in.Density;
double RPS = RPM/60.0;
// Calculate helical tip Mach
double Area = 0.25*Diameter*Diameter*M_PI;
double Vtip = RPS * Diameter * M_PI;
- HelicalTipMach = sqrt(Vtip*Vtip + Vel*Vel) / in.Soundspeed;
+ HelicalTipMach = sqrt(Vtip*Vtip + Vel*Vel) / in.Soundspeed;
PowerAvailable = EnginePower - GetPowerRequired();
if (RPS > 0.0) J = Vel / (Diameter * RPS); // Calculate J normally
- else J = Vel / Diameter;
+ else J = Vel / Diameter;
if (MaxPitch == MinPitch) { // Fixed pitch prop
- ThrustCoeff = cThrust->GetValue(J);
+ ThrustCoeff = cThrust->GetValue(J);
} else { // Variable pitch prop
- ThrustCoeff = cThrust->GetValue(J, Pitch);
+ ThrustCoeff = cThrust->GetValue(J, Pitch);
}
-
+
// Apply optional scaling factor to Ct (default value = 1)
ThrustCoeff *= CtFactor;
// Apply optional Mach effects from CT_MACH table
if (CtMach) ThrustCoeff *= CtMach->GetValue(HelicalTipMach);
- if (P_Factor > 0.0001) {
- SetActingLocationY( GetLocationY() + P_Factor*in.Alpha*Sense);
- SetActingLocationZ( GetLocationZ() + P_Factor*in.Beta*Sense);
- }
-
Thrust = ThrustCoeff*RPS*RPS*D4*rho;
- // From B. W. McCormick, "Aerodynamics, Aeronautics, and Flight Mechanics"
- // first edition, eqn. 6.15 (propeller analysis chapter).
- Vinduced = 0.5 * (-Vel + sqrt(Vel*Vel + 2.0*Thrust/(rho*Area)));
+ // Induced velocity in the propeller disk area. This formula is obtained
+ // from momentum theory - see B. W. McCormick, "Aerodynamics, Aeronautics,
+ // and Flight Mechanics" 1st edition, eqn. 6.15 (propeller analysis chapter).
+ // Since Thrust and Vel can both be negative we need to adjust this formula
+ // To handle sign (direction) separately from magnitude.
+ double Vel2sum = Vel*abs(Vel) + 2.0*Thrust/(rho*Area);
+
+ if( Vel2sum > 0.0)
+ Vinduced = 0.5 * (-Vel + sqrt(Vel2sum));
+ else
+ Vinduced = 0.5 * (-Vel - sqrt(-Vel2sum));
+
+ // We need to drop the case where the downstream velocity is opposite in
+ // direction to the aircraft velocity. For example, in such a case, the
+ // direction of the airflow on the tail would be opposite to the airflow on
+ // the wing tips. When such complicated airflows occur, the momentum theory
+ // breaks down and the formulas above are no longer applicable
+ // (see H. Glauert, "The Elements of Airfoil and Airscrew Theory",
+ // 2nd edition, ยง16.3, pp. 219-221)
+
+ if ((Vel+2.0*Vinduced)*Vel < 0.0)
+ Vinduced = 0.0; // We cannot calculate the induced velocity so let's assume it is zero.
+
+ // P-factor is simulated by a shift of the acting location of the thrust.
+ // The shift is a multiple of the angle between the propeller shaft axis
+ // and the relative wind that goes through the propeller disk.
+ if (P_Factor > 0.0001) {
+ double tangentialVel = localAeroVel.Magnitude(eV, eW);
+
+ if (tangentialVel > 0.0001) {
+ double angle = atan2(tangentialVel, localAeroVel(eU));
+ double factor = Sense * P_Factor * angle / tangentialVel;
+ SetActingLocationY( GetLocationY() + factor * localAeroVel(eW));
+ SetActingLocationZ( GetLocationZ() + factor * localAeroVel(eV));
+ }
+ }
omega = RPS*2.0*M_PI;
- vFn(1) = Thrust;
+ vFn(eX) = Thrust;
// The Ixx value and rotation speed given below are for rotation about the
// natural axis of the engine. The transform takes place in the base class
double RPS = RPM / 60.0;
if (RPS != 0.0) J = Vel / (Diameter * RPS);
- else J = Vel / Diameter;
+ else J = Vel / Diameter;
if (MaxPitch == MinPitch) { // Fixed pitch prop
cPReq = cPower->GetValue(J);
} else { // Manual Pitch Mode, pitch is controlled externally
}
-
+
cPReq = cPower->GetValue(J, Pitch);
}
double CL = (90.0 - Pitch) / 20.0;
if (CL > 1.5) CL = 1.5;
double BladeArea = Diameter * Diameter / 32.0 * numBlades;
- vTorque(eX) = -Sense*BladeArea*Diameter*Vel*Vel*rho*0.19*CL;
- PowerRequired = fabs(vTorque(eX))*0.2*M_PI;
+ vTorque(eX) = -Sense*BladeArea*Diameter*fabs(Vel)*Vel*rho*0.19*CL;
+ PowerRequired = Sense*(vTorque(eX))*0.2*M_PI;
}
return PowerRequired;
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-FGColumnVector3 FGPropeller::GetPFactor()
+FGColumnVector3 FGPropeller::GetPFactor() const
{
double px=0.0, py, pz;
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-string FGPropeller::GetThrusterLabels(int id, string delimeter)
+string FGPropeller::GetThrusterLabels(int id, const string& delimeter)
{
std::ostringstream buf;
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-string FGPropeller::GetThrusterValues(int id, string delimeter)
+string FGPropeller::GetThrusterValues(int id, const string& delimeter)
{
std::ostringstream buf;
projects / flightgear.git / blobdiff