FGPropeller Class Reference

Detailed Description

FGPropeller models a propeller given the tabular data for Ct (thrust) and Cp (power), indexed by the advance ratio "J".

Configuration File Format

<sense> {1 | -1} </sense> 
<p_factor> {number} </p_factor>
<propeller name="{string}" version="{string}">
  <ixx> {number} </ixx>
  <diameter unit="IN"> {number} </diameter>
  <numblades> {number} </numblades>
  <gearratio> {number} </gearratio>
  <minpitch> {number} </minpitch>
  <maxpitch> {number} </maxpitch>
  <minrpm> {number} </minrpm>
  <maxrpm> {number} </maxrpm>
  <constspeed> {number} </constspeed>
  <reversepitch> {number} </reversepitch>
  <ct_factor> {number} </ct_factor>
  <cp_factor> {number} </cp_factor>
 
  <table name="C_THRUST" type="internal">
    <tableData>
      {numbers}
    </tableData>
  </table>
 
  <table name="C_POWER" type="internal">
    <tableData>
      {numbers}
    </tableData>
  </table>
 
  <table name="CT_MACH" type="internal">
    <tableData>
      {numbers}
    </tableData>
  </table>
 
  <table name="CP_MACH" type="internal">
    <tableData>
      {numbers}
    </tableData>
  </table>
 
</propeller>

Configuration Parameters

    <ixx>           - Propeller rotational inertia.
    <diameter>      - Propeller disk diameter.
    <numblades>     - Number of blades.
    <gearratio>     - Ratio of (engine rpm) / (prop rpm).
    <minpitch>      - Minimum blade pitch angle.
    <maxpitch>      - Maximum blade pitch angle.
    <minrpm>        - Minimum rpm target for constant speed propeller.
    <maxrpm>        - Maximum rpm target for constant speed propeller.
    <constspeed>    - 1 = constant speed mode, 0 = manual pitch mode. 
    <reversepitch>  - Blade pitch angle for reverse.
    <sense>         - Direction of rotation (1=clockwise as viewed from cockpit,
                        -1=anti-clockwise as viewed from cockpit). Sense is
                       specified in the parent tag of the propeller.
    <p_factor>      - P factor. It is specified in the parent tag of
                       the propeller.
    <ct_factor>     - A multiplier for the coefficients of thrust.
    <cp_factor>     - A multiplier for the coefficients of power.

Two tables are needed. One for coefficient of thrust (Ct) and one for coefficient of power (Cp).

Two tables are optional. They apply a factor to Ct and Cp based on the helical tip Mach.

The parameters <sense> and <p_factor> must be specified at the parent level i.e. in the <thruster> element. This allows to specify different sense and P factor values for each propeller of the model while using the same definition file for all the propellers.

In addition to thrust, the propeller applies two moments to the aircraft:

• The torque that tends to roll the aircraft in the direction opposite to the propeller rotation,
• and the gyroscopic moment.

It should be noted that historically the gyroscopic moment had an incorrect sign. The correct sign can be obtained by specifying a version attribute higher than 1.0 to the propeller definition

<propeller name="a_prop" version="1.1">
  <!-- propeller definition -->
</propeller>

For backward compatibility, the absence of the version attribute will result in the gyroscopic moment to be computed with the legacy incorrect sign.

Several references were helpful, here:

• Barnes W. McCormick, "Aerodynamics, Aeronautics, and Flight Mechanics", Wiley & Sons, 1979 ISBN 0-471-03032-5
• Edwin Hartman, David Biermann, "The Aerodynamic Characteristics of Full Scale Propellers Having 2, 3, and 4 Blades of Clark Y and R.A.F. 6 Airfoil Sections", NACA Report TN-640, 1938 (?)
• Various NACA Technical Notes and Reports

Author

Jon S. Berndt

See also

FGEngine

FGThruster

Definition at line 169 of file FGPropeller.h.

#include <FGPropeller.h>

Inheritance diagram for FGPropeller:

Collaboration diagram for FGPropeller:

Public Member Functions
	FGPropeller (FGFDMExec *exec, Element *el, int num=0)
	Constructor for FGPropeller. More...
	~FGPropeller ()
	Destructor for FGPropeller - deletes the FGTable objects.
double	Calculate (double EnginePower)
	Calculates and returns the thrust produced by this propeller. More...
int	GetConstantSpeed (void) const
	Returns a non-zero value if the propeller is constant speed.
double	GetCpFactor (void) const
	Retrieves the coefficient of power multiplier.
FGTable *	GetCpMachTable (void) const
	Retrieves propeller power Mach effects factor.
FGTable *	GetCPowerTable (void) const
	Retrieves propeller power table.
double	GetCtFactor (void) const
	Retrieves the coefficient of thrust multiplier.
FGTable *	GetCThrustTable (void) const
	Retrieves propeller thrust table.
FGTable *	GetCtMachTable (void) const
	Retrieves propeller thrust Mach effects factor.
double	GetDiameter (void) const
	Retrieves the propeller diameter.
double	GetEngineRPM (void) const
	Calculates the RPMs of the engine based on gear ratio.
bool	GetFeather (void) const
	Returns true if the propeller is in feathered position.
double	GetHelicalTipMach (void) const
	Retrieves the Mach number at the propeller tips.
double	GetInducedVelocity (void) const
	Get the propeller induced velocity.
double	GetIxx (void) const
	Retrieves the propeller moment of inertia.
FGColumnVector3	GetPFactor (void) const
	Retrieves the P-Factor constant.
double	GetPitch (void) const
	Retrieves the pitch of the propeller in degrees.
double	GetPowerRequired (void)
	Retrieves the power required (or "absorbed") by the propeller - i.e. More...
bool	GetReverse (void) const
	Returns true if the propeller is in reverse position.
double	GetReverseCoef (void) const
	Retrieves the reverse pitch command.
double	GetRPM (void) const
	Retrieves the RPMs of the propeller.
double	GetThrustCoefficient (void) const
	Retrieves the thrust coefficient.
std::string	GetThrusterLabels (int id, const std::string &delimeter)
	Generate the labels for the thruster standard CSV output.
std::string	GetThrusterValues (int id, const std::string &delimeter)
	Generate the values for the thruster standard CSV output.
double	GetTorque (void) const
	Retrieves the Torque in foot-pounds (Don't you love the English system?)
bool	IsVPitch (void) const
	Returns true of this propeller is variable pitch.
void	ResetToIC (void)
	Reset the initial conditions.
void	SetAdvance (double advance)
	Set the propeller pitch. More...
void	SetConstantSpeed (int mode)
	Sets propeller into constant speed mode, or manual pitch mode.
void	SetCpFactor (double cpf)
	Sets coefficient of power multiplier.
void	SetCtFactor (double ctf)
	Sets coefficient of thrust multiplier.
void	SetEngineRPM (double rpm)
	Sets the Revolutions Per Minute for the propeller using the engine gear ratio.
void	SetFeather (bool f)
	If true, sets the propeller in feathered position.
void	SetInducedVelocity (double Vi)
	Set the propeller induced velocity.
void	SetPFactor (double pf)
	Sets the P-Factor constant.
void	SetPitch (double pitch)
	This commands the pitch of the blade to change to the value supplied. More...
void	SetReverse (bool r)
	If true, sets the propeller in reversed position.
void	SetReverseCoef (double c)
	Set the propeller reverse pitch. More...
void	SetRPM (double rpm)
	Sets the Revolutions Per Minute for the propeller. More...
void	SetSense (double s)
	Sets the rotation sense of the propeller. More...
Public Member Functions inherited from FGThruster
	FGThruster (FGFDMExec *FDMExec, Element *el, int num)
	Constructor.
virtual	~FGThruster ()
	Destructor.
double	GetGearRatio (void)
std::string	GetName (void)
double	GetReverserAngle (void) const
double	GetThrust (void) const
eType	GetType (void)
void	SetName (std::string name)
void	SetReverserAngle (double angle)
Public Member Functions inherited from FGForce
	FGForce (FGFDMExec *FDMExec)
	Constructor.
virtual	~FGForce ()
	Destructor.
const FGColumnVector3 &	GetActingLocation (void) const
double	GetActingLocationX (void) const
double	GetActingLocationY (void) const
double	GetActingLocationZ (void) const
double	GetAnglesToBody (int axis) const
const FGColumnVector3 &	GetAnglesToBody (void) const
virtual const FGColumnVector3 &	GetBodyForces (void)
double	GetBodyXForce (void) const
double	GetBodyYForce (void) const
double	GetBodyZForce (void) const
const FGColumnVector3 &	GetLocation (void) const
double	GetLocationX (void) const
double	GetLocationY (void) const
double	GetLocationZ (void) const
const FGColumnVector3 &	GetMoments (void) const
double	GetPitch (void) const
TransformType	GetTransformType (void) const
double	GetYaw (void) const
void	SetActingLocation (const FGColumnVector3 &vv)
void	SetActingLocation (double x, double y, double z)
	Acting point of application. More...
double	SetActingLocationX (double x)
double	SetActingLocationY (double y)
double	SetActingLocationZ (double z)
void	SetAnglesToBody (const FGColumnVector3 &vv)
void	SetAnglesToBody (double broll, double bpitch, double byaw)
void	SetLocation (const FGColumnVector3 &vv)
void	SetLocation (double x, double y, double z)
void	SetLocationX (double x)
void	SetLocationY (double y)
void	SetLocationZ (double z)
void	SetPitch (double pitch)
void	SetTransformType (TransformType ii)
void	SetYaw (double yaw)
const FGMatrix33 &	Transform (void) const
void	UpdateCustomTransformMatrix (void)
Public Member Functions inherited from FGJSBBase
	FGJSBBase ()
	Constructor for FGJSBBase.
virtual	~FGJSBBase ()
	Destructor for FGJSBBase.
void	disableHighLighting (void)
	Disables highlighting in the console output.

Additional Inherited Members
Public Types inherited from FGThruster
enum	eType { ttNozzle , ttRotor , ttPropeller , ttDirect }
Public Types inherited from FGForce
enum	TransformType {   tNone , tWindBody , tLocalBody , tInertialBody ,   tCustom }
Public Types inherited from FGJSBBase
enum	{ eL = 1 , eM , eN }
	Moments L, M, N.
enum	{ eP = 1 , eQ , eR }
	Rates P, Q, R.
enum	{ eU = 1 , eV , eW }
	Velocities U, V, W.
enum	{ eX = 1 , eY , eZ }
	Positions X, Y, Z.
enum	{ ePhi = 1 , eTht , ePsi }
	Euler angles Phi, Theta, Psi.
enum	{ eDrag = 1 , eSide , eLift }
	Stability axis forces, Drag, Side force, Lift.
enum	{ eRoll = 1 , ePitch , eYaw }
	Local frame orientation Roll, Pitch, Yaw.
enum	{ eNorth = 1 , eEast , eDown }
	Local frame position North, East, Down.
enum	{ eLat = 1 , eLong , eRad }
	Locations Radius, Latitude, Longitude.
enum	{   inNone = 0 , inDegrees , inRadians , inMeters ,   inFeet }
	Conversion specifiers.
Static Public Member Functions inherited from FGJSBBase
static const std::string &	GetVersion (void)
	Returns the version number of JSBSim. More...
static constexpr double	KelvinToFahrenheit (double kelvin)
	Converts from degrees Kelvin to degrees Fahrenheit. More...
static constexpr double	CelsiusToRankine (double celsius)
	Converts from degrees Celsius to degrees Rankine. More...
static constexpr double	RankineToCelsius (double rankine)
	Converts from degrees Rankine to degrees Celsius. More...
static constexpr double	KelvinToRankine (double kelvin)
	Converts from degrees Kelvin to degrees Rankine. More...
static constexpr double	RankineToKelvin (double rankine)
	Converts from degrees Rankine to degrees Kelvin. More...
static constexpr double	FahrenheitToCelsius (double fahrenheit)
	Converts from degrees Fahrenheit to degrees Celsius. More...
static constexpr double	CelsiusToFahrenheit (double celsius)
	Converts from degrees Celsius to degrees Fahrenheit. More...
static constexpr double	CelsiusToKelvin (double celsius)
	Converts from degrees Celsius to degrees Kelvin. More...
static constexpr double	KelvinToCelsius (double kelvin)
	Converts from degrees Kelvin to degrees Celsius. More...
static constexpr double	FeetToMeters (double measure)
	Converts from feet to meters. More...
static bool	EqualToRoundoff (double a, double b)
	Finite precision comparison. More...
static bool	EqualToRoundoff (float a, float b)
	Finite precision comparison. More...
static bool	EqualToRoundoff (float a, double b)
	Finite precision comparison. More...
static bool	EqualToRoundoff (double a, float b)
	Finite precision comparison. More...
static constexpr double	Constrain (double min, double value, double max)
	Constrain a value between a minimum and a maximum value.
static constexpr double	sign (double num)
Public Attributes inherited from FGThruster
struct JSBSim::FGThruster::Inputs	in
Static Public Attributes inherited from FGJSBBase
static char	highint [5] = {27, '[', '1', 'm', '\0' }
	highlights text
static char	halfint [5] = {27, '[', '2', 'm', '\0' }
	low intensity text
static char	normint [6] = {27, '[', '2', '2', 'm', '\0' }
	normal intensity text
static char	reset [5] = {27, '[', '0', 'm', '\0' }
	resets text properties
static char	underon [5] = {27, '[', '4', 'm', '\0' }
	underlines text
static char	underoff [6] = {27, '[', '2', '4', 'm', '\0' }
	underline off
static char	fgblue [6] = {27, '[', '3', '4', 'm', '\0' }
	blue text
static char	fgcyan [6] = {27, '[', '3', '6', 'm', '\0' }
	cyan text
static char	fgred [6] = {27, '[', '3', '1', 'm', '\0' }
	red text
static char	fggreen [6] = {27, '[', '3', '2', 'm', '\0' }
	green text
static char	fgdef [6] = {27, '[', '3', '9', 'm', '\0' }
	default text
static short	debug_lvl = 1
Static Protected Member Functions inherited from FGJSBBase
static std::string	CreateIndexedPropertyName (const std::string &Property, int index)
Protected Attributes inherited from FGThruster
int	EngineNum
double	GearRatio
std::string	Name
double	PowerRequired
double	ReverserAngle
double	Thrust
double	ThrustCoeff
eType	Type
Protected Attributes inherited from FGForce
FGFDMExec *	fdmex
std::shared_ptr< FGMassBalance >	MassBalance
FGMatrix33	mT
TransformType	ttype
FGColumnVector3	vActingXYZn
FGColumnVector3	vFn
FGColumnVector3	vMn
FGColumnVector3	vOrient
FGColumnVector3	vXYZn
Static Protected Attributes inherited from FGJSBBase
static constexpr double	radtodeg = 180. / M_PI
static constexpr double	degtorad = M_PI / 180.
static constexpr double	hptoftlbssec = 550.0
static constexpr double	psftoinhg = 0.014138
static constexpr double	psftopa = 47.88
static constexpr double	fttom = 0.3048
static constexpr double	ktstofps = 1852./(3600*fttom)
static constexpr double	fpstokts = 1.0 / ktstofps
static constexpr double	inchtoft = 1.0/12.0
static constexpr double	m3toft3 = 1.0/(fttom*fttom*fttom)
static constexpr double	in3tom3 = inchtoft*inchtoft*inchtoft/m3toft3
static constexpr double	inhgtopa = 3386.38
static constexpr double	slugtolb = 32.174049
	Note that definition of lbtoslug by the inverse of slugtolb and not to a different constant you can also get from some tables will make lbtoslug*slugtolb == 1 up to the magnitude of roundoff. More...
static constexpr double	lbtoslug = 1.0/slugtolb
static constexpr double	kgtolb = 2.20462
static constexpr double	kgtoslug = 0.06852168
static const std::string	needed_cfg_version = "2.0"
static const std::string	JSBSim_version = JSBSIM_VERSION " " __DATE__ " " __TIME__

Constructor & Destructor Documentation

FGPropeller()

FGPropeller	(	FGFDMExec *	exec,
		Element *	el,
		int	num = 0
	)

Constructor for FGPropeller.

Parameters

exec	a pointer to the main executive object
el	a pointer to the thruster config file XML element
num	the number of this propeller

Definition at line 53 of file FGPropeller.cpp.

                       : FGThruster(exec, prop_element, num)
{
  Element *table_element, *local_element;
  string name="";
  auto PropertyManager = exec->GetPropertyManager();
 
  MaxPitch = MinPitch = P_Factor = Pitch = Advance = MinRPM = MaxRPM = 0.0;
  Sense = 1; // default clockwise rotation
  ReversePitch = 0.0;
  Reversed = false;
  Feathered = false;
  Reverse_coef = 0.0;
  GearRatio = 1.0;
  CtFactor = CpFactor = 1.0;
  ConstantSpeed = 0;
  cThrust = cPower = CtMach = CpMach = 0;
  Vinduced = 0.0;
 
  if (prop_element->FindElement("ixx"))
    Ixx = max(prop_element->FindElementValueAsNumberConvertTo("ixx", "SLUG*FT2"), 1e-06);
 
  Sense_multiplier = 1.0;
  if (prop_element->HasAttribute("version")
      && prop_element->GetAttributeValueAsNumber("version") > 1.0)
      Sense_multiplier = -1.0;
 
  if (prop_element->FindElement("diameter"))
    Diameter = max(prop_element->FindElementValueAsNumberConvertTo("diameter", "FT"), 0.001);
  if (prop_element->FindElement("numblades"))
    numBlades = (int)prop_element->FindElementValueAsNumber("numblades");
  if (prop_element->FindElement("gearratio"))
    GearRatio = max(prop_element->FindElementValueAsNumber("gearratio"), 0.001);
  if (prop_element->FindElement("minpitch"))
    MinPitch = prop_element->FindElementValueAsNumber("minpitch");
  if (prop_element->FindElement("maxpitch"))
    MaxPitch = prop_element->FindElementValueAsNumber("maxpitch");
  if (prop_element->FindElement("minrpm"))
    MinRPM = prop_element->FindElementValueAsNumber("minrpm");
  if (prop_element->FindElement("maxrpm")) {
    MaxRPM = prop_element->FindElementValueAsNumber("maxrpm");
    ConstantSpeed = 1;
    }
  if (prop_element->FindElement("constspeed"))
    ConstantSpeed = (int)prop_element->FindElementValueAsNumber("constspeed");
  if (prop_element->FindElement("reversepitch"))
    ReversePitch = prop_element->FindElementValueAsNumber("reversepitch");
  while((table_element = prop_element->FindNextElement("table")) != 0) {
    name = table_element->GetAttributeValue("name");
    try {
      if (name == "C_THRUST") {
        cThrust = new FGTable(PropertyManager, table_element);
      } else if (name == "C_POWER") {
        cPower = new FGTable(PropertyManager, table_element);
      } else if (name == "CT_MACH") {
        CtMach = new FGTable(PropertyManager, table_element);
      } else if (name == "CP_MACH") {
        CpMach = new FGTable(PropertyManager, table_element);
      } else {
        cerr << "Unknown table type: " << name << " in propeller definition." << endl;
      }
    } catch (std::string& str) {
      throw("Error loading propeller table:" + name + ". " + str);
    }
  }
  if( (cPower == 0) || (cThrust == 0)){
      cerr << "Propeller configuration must contain C_THRUST and C_POWER tables!" << endl;
  }
 
  local_element = prop_element->GetParent()->FindElement("sense");
  if (local_element) {
    double Sense = local_element->GetDataAsNumber();
    SetSense(Sense >= 0.0 ? 1.0 : -1.0);
  }
  local_element = prop_element->GetParent()->FindElement("p_factor");
  if (local_element) {
    P_Factor = local_element->GetDataAsNumber();
  }
  if (P_Factor < 0) {
    cerr << "P-Factor value in propeller configuration file must be greater than zero" << endl;
  }
  if (prop_element->FindElement("ct_factor"))
    SetCtFactor( prop_element->FindElementValueAsNumber("ct_factor") );
  if (prop_element->FindElement("cp_factor"))
    SetCpFactor( prop_element->FindElementValueAsNumber("cp_factor") );
 
  Type = ttPropeller;
  RPM = 0;
  vTorque.InitMatrix();
  D4 = Diameter*Diameter*Diameter*Diameter;
  D5 = D4*Diameter;
  Pitch = MinPitch;
 
  string property_name, base_property_name;
  base_property_name = CreateIndexedPropertyName("propulsion/engine", EngineNum);
  property_name = base_property_name + "/engine-rpm";
  PropertyManager->Tie( property_name.c_str(), this, &FGPropeller::GetEngineRPM );
  property_name = base_property_name + "/advance-ratio";
  PropertyManager->Tie( property_name.c_str(), &J );
  property_name = base_property_name + "/blade-angle";
  PropertyManager->Tie( property_name.c_str(), &Pitch );
  property_name = base_property_name + "/thrust-coefficient";
  PropertyManager->Tie( property_name.c_str(), this, &FGPropeller::GetThrustCoefficient );
  property_name = base_property_name + "/propeller-rpm";
  PropertyManager->Tie( property_name.c_str(), this, &FGPropeller::GetRPM );
  property_name = base_property_name + "/helical-tip-Mach";
  PropertyManager->Tie( property_name.c_str(), this, &FGPropeller::GetHelicalTipMach );
  property_name = base_property_name + "/constant-speed-mode";
  PropertyManager->Tie( property_name.c_str(), this, &FGPropeller::GetConstantSpeed,
                      &FGPropeller::SetConstantSpeed );
  property_name = base_property_name + "/prop-induced-velocity_fps"; // [ft/sec]
  PropertyManager->Tie( property_name.c_str(), this, &FGPropeller::GetInducedVelocity,
                      &FGPropeller::SetInducedVelocity );
  property_name = base_property_name + "/propeller-power-ftlbps"; // [ft-lbs/sec]
  PropertyManager->Tie( property_name.c_str(), &PowerRequired );
  property_name = base_property_name + "/propeller-torque-ftlb"; // [ft-lbs]
  PropertyManager->Tie( property_name.c_str(), this, &FGPropeller::GetTorque);
  property_name = base_property_name + "/propeller-sense";
  PropertyManager->Tie( property_name.c_str(), &Sense );
 
  Debug(0);
}

Here is the call graph for this function:

Member Function Documentation

Calculate()

double Calculate ( double  EnginePower )

virtual

Calculates and returns the thrust produced by this propeller.

Given the excess power available from the engine (in foot-pounds), 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).

Parameters

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.

Returns

the thrust in pounds

Reimplemented from FGThruster.

Definition at line 207 of file FGPropeller.cpp.

{
  FGColumnVector3 vDXYZ = MassBalance->StructuralToBody(vXYZn);
  const FGMatrix33& mT = Transform();
  // Local air velocity is obtained from Stevens & Lewis' "Aircraft Control and
  // Simualtion (3rd edition)" eqn 8.2-1
  // Variables in.AeroUVW and in.AeroPQR include the wind and turbulence effects
  // as computed by FGAuxiliary.
  FGColumnVector3 localAeroVel = mT.Transposed() * (in.AeroUVW + in.AeroPQR*vDXYZ);
  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 > 0.01) 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;
  vTorque(eX) = -Sense*EnginePower / max(0.01, omega);
 
  // 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 > 0.01) 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*(mT*vH) + mT*vTorque;
 
  return Thrust; // return thrust in pounds
}

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GetPowerRequired()

double GetPowerRequired ( void  )

virtual

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.

Reimplemented from FGThruster.

Definition at line 302 of file FGPropeller.cpp.

{
  double cPReq;
 
  if (MaxPitch == MinPitch) {   // Fixed pitch prop
    cPReq = cPower->GetValue(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 compatiblity, 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 > 200) Pitch -= dRPM * in.TotalDeltaT;
          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 > 200) Pitch += (PitchReq - Pitch) / 200;
          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) / 300; // just a guess (about 5 sec to fully feathered)
      }
 
    } else { // Manual Pitch Mode, pitch is controlled externally
 
    }
 
    cPReq = cPower->GetValue(J, Pitch);
  }
 
  // Apply optional scaling factor to Cp (default value = 1)
  cPReq *= CpFactor;
 
  // Apply optional Mach effects from CP_MACH table
  if (CpMach) cPReq *= CpMach->GetValue(HelicalTipMach);
 
  double RPS = RPM / 60.0;
  double local_RPS = RPS < 0.01 ? 0.01 : RPS; 
 
  PowerRequired = cPReq*local_RPS*local_RPS*local_RPS*D5*in.Density;
 
  return PowerRequired;
}

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SetAdvance()

void SetAdvance ( double  advance )

inline

Set the propeller pitch.

Parameters

advance

the pitch command in percent (0.0 - 1.0)

Definition at line 211 of file FGPropeller.h.

{Advance = advance;}

SetPitch()

void SetPitch ( double  pitch )

inline

This commands the pitch of the blade to change to the value supplied.

This call is meant to be issued either from the cockpit or by the flight control system (perhaps to maintain constant RPM for a constant-speed propeller). This value will be limited to be within whatever is specified in the config file for Max and Min pitch. It is also one of the lookup indices to the power and thrust tables for variable-pitch propellers.

Parameters

pitch

the pitch of the blade in degrees.

Definition at line 206 of file FGPropeller.h.

{Pitch = pitch;}

SetReverseCoef()

void SetReverseCoef ( double  c )

inline

Set the propeller reverse pitch.

Parameters

c	the reverse pitch command in percent (0.0 - 1.0)

Definition at line 289 of file FGPropeller.h.

{ Reverse_coef = c; }

SetRPM()

void SetRPM ( double  rpm )

inlinevirtual

Sets the Revolutions Per Minute for the propeller.

Normally the propeller instance will calculate its own rotational velocity, given the Torque produced by the engine and integrating over time using the standard equation for rotational acceleration \(a\): \(a = Q/I\) , where \(Q\) is Torque and \(I\) is moment of inertia for the propeller.

Parameters

rpm	the rotational velocity of the propeller

Reimplemented from FGThruster.

Definition at line 190 of file FGPropeller.h.

{RPM = rpm;}

SetSense()

void SetSense ( double  s )

inline

Sets the rotation sense of the propeller.

Parameters

s	this value should be +/- 1 ONLY. +1 indicates clockwise rotation as viewed by someone standing behind the engine looking forward into the direction of flight.

Definition at line 229 of file FGPropeller.h.

{ Sense = s;}

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---

The documentation for this class was generated from the following files:

• FGPropeller.h
• FGPropeller.cpp