Exemplo n.º 1
0
FGColumnVector3 FGPropeller::GetPFactor()
{
  double px=0.0, py, pz;

  py = Thrust * Sense * (GetActingLocationY() - GetLocationY()) / 12.0;
  pz = Thrust * Sense * (GetActingLocationZ() - GetLocationZ()) / 12.0;

  return FGColumnVector3(px, py, pz);
}
Exemplo n.º 2
0
FGColumnVector3 FGPropeller::GetPFactor() const
{
  // These are moments in lbf per ft : the lever arm along Z generates a moment
  // along the pitch direction.
  double p_pitch = Thrust * Sense * (GetActingLocationZ() - GetLocationZ()) / 12.0;
  // The lever arm along Y generates a moment along the yaw direction.
  double p_yaw = Thrust * Sense * (GetActingLocationY() - GetLocationY()) / 12.0;

  return FGColumnVector3(0.0, p_pitch, p_yaw);
}
Exemplo n.º 3
0
double FGPropeller::Calculate(double PowerAvailable)
{
  double omega, alpha, beta;

  double Vel = fdmex->GetAuxiliary()->GetAeroUVW(eU);
  double rho = fdmex->GetAtmosphere()->GetDensity();
  double RPS = RPM/60.0;

  if (RPS > 0.00) J = Vel / (Diameter * RPS); // Calculate J normally
  else            J = 1000.0;                 // Set J to a high number

  if (MaxPitch == MinPitch)  ThrustCoeff = cThrust->GetValue(J);
  else                       ThrustCoeff = cThrust->GetValue(J, Pitch);
  ThrustCoeff *= CtFactor;

  if (P_Factor > 0.0001) {
    alpha = fdmex->GetAuxiliary()->Getalpha();
    beta  = fdmex->GetAuxiliary()->Getbeta();
    SetActingLocationY( GetLocationY() + P_Factor*alpha*Sense);
    SetActingLocationZ( GetLocationZ() + P_Factor*beta*Sense);
  }

  Thrust = ThrustCoeff*RPS*RPS*D4*rho;
  omega = RPS*2.0*M_PI;

  vFn(1) = 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
  // FGForce::GetBodyForces() function.

  vH(eX) = Ixx*omega*Sense;
  vH(eY) = 0.0;
  vH(eZ) = 0.0;

  if (omega > 0.0) ExcessTorque = GearRatio * PowerAvailable / omega;
  else             ExcessTorque = GearRatio * PowerAvailable / 1.0;

  RPM = (RPS + ((ExcessTorque / Ixx) / (2.0 * M_PI)) * deltaT) * 60.0;

  if (RPM < 1.0) RPM = 0; // Engine friction stops rotation arbitrarily at 1 RPM.

  vMn = fdmex->GetPropagate()->GetPQR()*vH + vTorque;

  return Thrust; // return thrust in pounds
}
Exemplo n.º 4
0
double FGPropeller::Calculate(double EnginePower)
{
  FGColumnVector3 localAeroVel = Transform().Transposed() * in.AeroUVW;
  double omega, PowerAvailable;

  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;

  PowerAvailable = EnginePower - GetPowerRequired();

  if (RPS > 0.0) J = Vel / (Diameter * RPS); // Calculate J normally
  else           J = Vel / Diameter;

  if (MaxPitch == MinPitch) {    // Fixed pitch prop
    ThrustCoeff = cThrust->GetValue(J);
  } else {                       // Variable pitch prop
    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);

  Thrust = ThrustCoeff*RPS*RPS*D4*rho;

  // 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, §16.3, 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*2.0*M_PI;

  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
  // FGForce::GetBodyForces() function.

  vH(eX) = Ixx*omega*Sense;
  vH(eY) = 0.0;
  vH(eZ) = 0.0;

  if (omega > 0.0) ExcessTorque = PowerAvailable / omega;
  else             ExcessTorque = PowerAvailable / 1.0;

  RPM = (RPS + ((ExcessTorque / Ixx) / (2.0 * M_PI)) * deltaT) * 60.0;

  if (RPM < 0.0) RPM = 0.0; // 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;

  return Thrust; // return thrust in pounds
}
Exemplo n.º 5
0
double FGPropeller::Calculate(double EnginePower)
{
  FGColumnVector3 localAeroVel = Transform().Transposed() * in.AeroUVW;
  double omega, PowerAvailable;

  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;

  if (RPS > 0.0) J = Vel / (Diameter * RPS); // Calculate J normally
  else           J = Vel / Diameter;

  PowerAvailable = EnginePower - GetPowerRequired();

  if (MaxPitch == MinPitch) {    // Fixed pitch prop
    ThrustCoeff = cThrust->GetValue(J);
  } else {                       // Variable pitch prop
    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);

  Thrust = ThrustCoeff*RPS*RPS*D4*rho;

  // 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));
    
  // 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) {
      // The angle made locally by the air flow with respect to the propeller
      // axis is influenced by the induced velocity. This attenuates the
      // influence of a string cross wind and gives a more realistic behavior.
      double angle = atan2(tangentialVel, Vel+Vinduced);
      double factor = Sense * P_Factor * angle / tangentialVel;
      SetActingLocationY( GetLocationY() + factor * localAeroVel(eW));
      SetActingLocationZ( GetLocationZ() + factor * localAeroVel(eV));
    }
  }

  omega = RPS*2.0*M_PI;

  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
  // FGForce::GetBodyForces() function.

  FGColumnVector3 vH(Ixx*omega*Sense*Sense_multiplier, 0.0, 0.0);

  if (omega > 0.0) ExcessTorque = PowerAvailable / omega;
  else             ExcessTorque = PowerAvailable / 1.0;

  RPM = (RPS + ((ExcessTorque / Ixx) / (2.0 * M_PI)) * in.TotalDeltaT) * 60.0;

  if (RPM < 0.0) RPM = 0.0; // Engine won't turn backwards

  // Transform Torque and momentum first, as PQR is used in this
  // equation and cannot be transformed itself.
  vMn = in.PQRi*(Transform()*vH) + Transform()*vTorque;

  return Thrust; // return thrust in pounds
}