/** Calculates and returns the thrust produced by this propeller.
* Given the excess power available from the engine (in watts), the thrust is
* calculated, as well as the current RPM. The RPM is calculated by integrating
* the torque provided by the engine over what the propeller "absorbs"
* (essentially the "drag" of the propeller).
* @param PowerAvailable this is the excess power provided by the engine to
* accelerate the prop. It could be negative, dictating that the propeller
* would be slowed.
* @return the thrust in newtons */
public double Calculate(double EnginePower, double rho, double Vel, double speedOfSound, double deltaTime)
{
deltaT = deltaTime;
double omega, PowerAvailable;
double RPS = RPM * (1d / 60d);
double machInv = 1d / speedOfSound;
// Calculate helical tip Mach
double Area = 0.25d * Diameter * Diameter * Math.PI;
double Vtip = RPS * Diameter * Math.PI;
HelicalTipMach = Math.Sqrt(Vtip * Vtip + Vel * Vel) * machInv;
PowerAvailable = EnginePower - GetPowerRequired(rho, Vel);
if (RPS > 0d)
{
J = Vel / (Diameter * RPS); // Calculate J normally
}
else
{
J = Vel / Diameter;
}
if (MaxPitch == MinPitch) // Fixed pitch prop
{
ThrustCoeff = cThrustFP.Evaluate((float)J);
}
else // Variable pitch prop
{
ThrustCoeff = cThrust.GetValue(J, Pitch);
}
// Apply optional scaling factor to Ct (default value = 1)
ThrustCoeff *= CtFactor * CtTweak;
// Apply optional Mach effects from CT_MACH table
double CtMachFactor = 1;
if (CtMach != null)
{
CtMachFactor = Math.Pow(CtMach.Evaluate((float)HelicalTipMach), MachPowTweak);
ThrustCoeff *= CtMachFactor;
}
Thrust = ThrustCoeff * RPS * RPS * D4 * rho;
//Debug.Log("CT = " + ThrustCoeff + " CtFactor = " + CtFactor + "\n\rCtTweak = " + CtTweak + " CtMachFactor = " + CtMachFactor + "\n\rJ = " + J + "\n\rHelicalTipMach = " + HelicalTipMach + " SoundSpeed = " + speedOfSound);
/*// 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*Math.Abs(Vel) + 2.0*Thrust/(rho*Area);
*
* if( Vel2sum > 0.0)
* Vinduced = 0.5 * (-Vel + Math.Sqrt(Vel2sum));
* else
* Vinduced = 0.5 * (-Vel - Math.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, ?6.3, pp. 219-221)
*
* if ((Vel+2.0*Vinduced)*Vel < 0.0)
* // The momentum theory is no longer applicable so let's assume the induced
* // saturates to -0.5*Vel so that the total velocity Vel+2*Vinduced equals 0.
* Vinduced = -0.5*Vel;
*
* // 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 * 2d * Math.PI;
// 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
// FGForce::GetBodyForces() function.
/*vH(eX) = Ixx*omega*Sense;
* vH(eY) = 0.0;
* vH(eZ) = 0.0;*/
if (omega > 0d)
{
ExcessTorque = PowerAvailable / omega;
}
else
{
ExcessTorque = PowerAvailable;
}
RPM = (RPS + (ExcessTorque / (Ixx * 2.0 * Math.PI) * deltaT)) * 60d;
if (RPM < 0d)
{
RPM = 0d; // Engine won't turn backwards
}
// Transform Torque and momentum first, as PQR is used in this
// equation and cannot be transformed itself.
//vMn = in.PQR*(Transform()*vH) + Transform()*vTorque;
// hacky mach drag -- should not be needed with nuFAR
/*if (MachDrag != null)
* {
* double machDrag = MachDrag.Evaluate((float)(Vel * machInv));
* machDrag *= machDrag * D4 * RPS * RPS * rho * 0.00004d;
* Thrust -= machDrag;
* }*/
//MonoBehaviour.print("Prop running: thrust " + Thrust + ", Ct " + ThrustCoeff + ", RPM " + RPM + ", PAvail " + PowerAvailable + ", J " + J + ", delta RPM " + (RPM - RPS * 60d));
return(Thrust);
}
/*public Vector3 GetPFactor()
* {
* double px = 0.0, py, pz;
*
* py = Thrust * Sense * (ActingLocation.y - GetLocationY()) / 12.0;
* pz = Thrust * Sense * (ActingLocation.z - GetLocationZ()) / 12.0;
*
* return Vector3(px, py, pz);
* }*/
/** Retrieves the power required (or "absorbed") by the propeller -
* i.e. the power required to keep spinning the propeller at the current
* velocity, air density, and rotational rate. */
public double GetPowerRequired(double rho, double Vel)
{
double cPReq, J;
double RPS = RPM * (1d / 60d);
if (RPS != 0d)
{
J = Vel / (Diameter * RPS);
}
else
{
J = Vel / Diameter;
}
if (MaxPitch == MinPitch) // Fixed pitch prop
{
cPReq = cPowerFP.Evaluate((float)J);
}
else
{ // Variable pitch prop
if (ConstantSpeed != 0) // Constant Speed Mode
{
// do normal calculation when propeller is neither feathered nor reversed
// Note: This method of feathering and reversing was added to support the
// turboprop model. It's left here for backward compatablity, but
// now feathering and reversing should be done in Manual Pitch Mode.
if (!Feathered)
{
if (!Reversed)
{
double rpmReq = MinRPM + (MaxRPM - MinRPM) * Advance;
double dRPM = rpmReq - RPM;
// The pitch of a variable propeller cannot be changed when the RPMs are
// too low - the oil pump does not work.
if (RPM > 200d)
{
Pitch -= dRPM * deltaT;
}
if (Pitch < MinPitch)
{
Pitch = MinPitch;
}
else if (Pitch > MaxPitch)
{
Pitch = MaxPitch;
}
}
else // Reversed propeller
{
// when reversed calculate propeller pitch depending on throttle lever position
// (beta range for taxing full reverse for braking)
double PitchReq = MinPitch - (MinPitch - ReversePitch) * Reverse_coef;
// The pitch of a variable propeller cannot be changed when the RPMs are
// too low - the oil pump does not work.
if (RPM > 200d)
{
Pitch += (PitchReq - Pitch) * (1d / 200d);
}
if (RPM > MaxRPM)
{
Pitch += (MaxRPM - RPM) / 50;
if (Pitch < ReversePitch)
{
Pitch = ReversePitch;
}
else if (Pitch > MaxPitch)
{
Pitch = MaxPitch;
}
}
}
}
else // Feathered propeller
{
// ToDo: Make feathered and reverse settings done via FGKinemat
Pitch += (MaxPitch - Pitch) * (1d / 300d); // just a guess (about 5 sec to fully feathered)
if (Pitch > MaxPitch)
{
Pitch = MaxPitch;
}
}
}
else // Manual Pitch Mode, pitch is controlled externally
{
}
cPReq = cPower.GetValue(J, Pitch);
}
// Apply optional scaling factor to Cp (default value = 1)
cPReq *= CpFactor * CpTweak;
// Apply optional Mach effects from CP_MACH table
if (CpMach != null)
{
cPReq *= Math.Pow(CpMach.Evaluate((float)HelicalTipMach), MachPowTweak);
}
double local_RPS = RPS < 0.01d ? 0.01d : RPS;
PowerRequired = cPReq * local_RPS * local_RPS * local_RPS * D5 * rho;
vTorque.x = (-Sense * PowerRequired / (local_RPS * 2.0 * Math.PI));
//Debug.Log("Cp = " + cPReq);
return(PowerRequired);
}
