Detailed Description

Utility class that handles power transmission in conjunction with FGRotor.

This class provides brake, clutch and free-wheel-unit (FWU) functionality for the rotor model. Also it is responsible for the RPM calculations.

When the engine is off the brake could be used to slow/hold down a spinning rotor. The maximum brake power is defined in the rotors' config file. (Right now there is no checking if the input is in the [0..1] range.)

The clutch operation is based on a heuristic approach. In the intermediate state the transfer is proportional to the clutch position. But equal RPM values are enforced on the thruster and rotor sides when approaching the closed state.

The FWU inhibits that the rotor is driving the engine. To do so, the code just predicts the upcoming FWU state based on current torque conditions.

Some engines won't work properly when the clutch is open. To keep them controllable some load must be provided on the engine side (EngineFriction, aka gear-loss). See the notes under 'Engine issues' in FGRotor.

Property tree

The following properties are created (with x = your thruster number):

    propulsion/engine[x]/brake-ctrl-norm
    propulsion/engine[x]/free-wheel-transmission
    propulsion/engine[x]/clutch-ctrl-norm

Notes

EngineFriction is assumed constant, so better orientate at low RPM values, because piston and turboprop engines don't 'like' high load at startup.
The model doesn't support backward operation.
And even worse, the torque calculations silently assume a minimal RPM value of approx. 1.

Definition at line 108 of file FGTransmission.h.

#include <FGTransmission.h>

Inheritance diagram for FGTransmission:

Collaboration diagram for FGTransmission:

Public Member Functions
	FGTransmission (FGFDMExec *exec, int num, double dt)
	Constructor for FGTransmission.

	~FGTransmission ()
	Destructor for FGTransmission.

void	Calculate (double EnginePower, double ThrusterTorque, double dt)

double	GetBrakeCtrlNorm () const

double	GetClutchCtrlNorm () const

double	GetEngineFriction () const

double	GetEngineMoment () const

double	GetEngineRPM ()

double	GetFreeWheelTransmission () const

double	GetMaxBrakePower () const

double	GetThrusterMoment () const

double	GetThrusterRPM ()

void	ResetToIC (void)
	Reset the initial conditions.

void	SetBrakeCtrlNorm (double x)

void	SetClutchCtrlNorm (double x)

void	SetEngineFriction (double x)

void	SetEngineMoment (double x)

void	SetEngineRPM (double x)

void	SetMaxBrakePower (double x)

void	SetThrusterMoment (double x)

void	SetThrusterRPM (double x)

Public Member Functions inherited from FGJSBBase
	FGJSBBase ()
	Constructor for FGJSBBase.

virtual	~FGJSBBase ()
	Destructor for FGJSBBase.

Additional Inherited Members
Public Types inherited from FGJSBBase
enum	{ eL = 1 , eM , eN }
	Moments L, M, N. More...

enum	{ eP = 1 , eQ , eR }
	Rates P, Q, R. More...

enum	{ eU = 1 , eV , eW }
	Velocities U, V, W. More...

enum	{ eX = 1 , eY , eZ }
	Positions X, Y, Z. More...

enum	{ ePhi = 1 , eTht , ePsi }
	Euler angles Phi, Theta, Psi. More...

enum	{ eDrag = 1 , eSide , eLift }
	Stability axis forces, Drag, Side force, Lift. More...

enum	{ eRoll = 1 , ePitch , eYaw }
	Local frame orientation Roll, Pitch, Yaw. More...

enum	{ eNorth = 1 , eEast , eDown }
	Local frame position North, East, Down. More...

enum	{ eLat = 1 , eLong , eRad }
	Locations Radius, Latitude, Longitude. More...

enum	{ inNone = 0 , inDegrees , inRadians , inMeters , inFeet }
	Conversion specifiers. More...

Static Public Member Functions inherited from FGJSBBase
static constexpr double	CelsiusToFahrenheit (double celsius)
	Converts from degrees Celsius to degrees Fahrenheit.

static constexpr double	CelsiusToKelvin (double celsius)
	Converts from degrees Celsius to degrees Kelvin.

static constexpr double	CelsiusToRankine (double celsius)
	Converts from degrees Celsius to degrees Rankine.

static constexpr double	Constrain (double min, double value, double max)
	Constrain a value between a minimum and a maximum value.

static bool	EqualToRoundoff (double a, double b)
	Finite precision comparison.

static bool	EqualToRoundoff (double a, float b)
	Finite precision comparison.

static bool	EqualToRoundoff (float a, double b)
	Finite precision comparison.

static bool	EqualToRoundoff (float a, float b)
	Finite precision comparison.

static constexpr double	FahrenheitToCelsius (double fahrenheit)
	Converts from degrees Fahrenheit to degrees Celsius.

static constexpr double	FeetToMeters (double measure)
	Converts from feet to meters.

static const std::string &	GetVersion (void)
	Returns the version number of JSBSim.

static constexpr double	KelvinToCelsius (double kelvin)
	Converts from degrees Kelvin to degrees Celsius.

static constexpr double	KelvinToFahrenheit (double kelvin)
	Converts from degrees Kelvin to degrees Fahrenheit.

static constexpr double	KelvinToRankine (double kelvin)
	Converts from degrees Kelvin to degrees Rankine.

static constexpr double	RankineToCelsius (double rankine)
	Converts from degrees Rankine to degrees Celsius.

static constexpr double	RankineToKelvin (double rankine)
	Converts from degrees Rankine to degrees Kelvin.

static constexpr double	sign (double num)

Static Public Attributes inherited from FGJSBBase
static short	debug_lvl = 1

Static Protected Member Functions inherited from FGJSBBase
static std::string	CreateIndexedPropertyName (const std::string &Property, int index)

Static Protected Attributes inherited from FGJSBBase
static constexpr double	degtorad = M_PI / 180.

static constexpr double	fpstokts = 1.0 / ktstofps

static constexpr double	fttom = 0.3048

static constexpr double	hptoftlbssec = 550.0

static constexpr double	in3tom3 = inchtoftinchtoftinchtoft/m3toft3

static constexpr double	inchtoft = 1.0/12.0

static constexpr double	inhgtopa = 3386.38

static const std::string	JSBSim_version = JSBSIM_VERSION " " __DATE__ " " __TIME__

static constexpr double	kgtolb = 2.20462

static constexpr double	kgtoslug = 0.06852168

static constexpr double	ktstofps = 1852./(3600*fttom)

static constexpr double	lbtoslug = 1.0/slugtolb

static constexpr double	m3toft3 = 1.0/(fttomfttomfttom)

static const std::string	needed_cfg_version = "2.0"

static constexpr double	psftoinhg = 0.014138

static constexpr double	psftopa = 47.88

static constexpr double	radtodeg = 180. / M_PI

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.

Constructor & Destructor Documentation

◆ FGTransmission()

FGTransmission	(	FGFDMExec *	exec,
		int	num,
		double	dt
	)

Constructor for FGTransmission.

Parameters

exec	a pointer to the main executive object
num	the number of the thruster that uses this object
dt	simulation delta T

Definition at line 53 of file FGTransmission.cpp.

                                                                  :
  ThrusterMoment(1.0), EngineMoment(1.0), EngineFriction(0.0),
  ClutchCtrlNorm(1.0), BrakeCtrlNorm(0.0), MaxBrakePower(0.0)
{
  auto PropertyManager = exec->GetPropertyManager();
  FreeWheelLag = Filter(200.0,dt); // avoid too abrupt changes in transmission
  InitDynamics();
  BindModel(num, PropertyManager.get());
}

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◆ ~FGTransmission()

~FGTransmission ( )

Destructor for FGTransmission.

Definition at line 65 of file FGTransmission.cpp.

65 {

66}

Member Function Documentation

◆ Calculate()

void Calculate	(	double	EnginePower,
		double	ThrusterTorque,
		double	dt
	)

Definition at line 88 of file FGTransmission.cpp.

                                                                                   {
 
  double coupling = 1.0, coupling_sq = 1.0;
  double fw_mult = 1.0;
 
  double d_omega = 0.0, engine_d_omega = 0.0, thruster_d_omega = 0.0; // relative changes
 
  double engine_omega = rpm_to_omega(EngineRPM);
  double safe_engine_omega = engine_omega < 1e-1 ? 1e-1 : engine_omega;
  double engine_torque = EnginePower / safe_engine_omega;
 
  double thruster_omega = rpm_to_omega(ThrusterRPM);
  double safe_thruster_omega = thruster_omega < 1e-1 ? 1e-1 : thruster_omega;
 
  engine_torque  -= EngineFriction / safe_engine_omega;
  ThrusterTorque += Constrain(0.0, BrakeCtrlNorm, 1.0) * MaxBrakePower / safe_thruster_omega;
 
  // would the FWU release ?
  engine_d_omega = engine_torque/EngineMoment * dt;
  thruster_d_omega =  - ThrusterTorque/ThrusterMoment * dt;
 
  if ( thruster_omega+thruster_d_omega > engine_omega+engine_d_omega ) {
    // don't drive the engine
    FreeWheelTransmission = 0.0;
  } else {
    FreeWheelTransmission = 1.0;
  }
 
  fw_mult = FreeWheelLag.execute(FreeWheelTransmission);
  coupling = fw_mult * Constrain(0.0, ClutchCtrlNorm, 1.0);
 
  if (coupling < 0.999999) { // are the separate calculations needed ?
    // assume linear transfer
    engine_d_omega   =
       (engine_torque - ThrusterTorque*coupling)/(ThrusterMoment*coupling + EngineMoment) * dt;
    thruster_d_omega =
       (engine_torque*coupling - ThrusterTorque)/(ThrusterMoment + EngineMoment*coupling) * dt;
 
    EngineRPM += omega_to_rpm(engine_d_omega);
    ThrusterRPM += omega_to_rpm(thruster_d_omega);
 
    // simulate transit to static friction
    coupling_sq = coupling*coupling;
    EngineRPM   = (1.0-coupling_sq) * EngineRPM    + coupling_sq * 0.02 * (49.0*EngineRPM + ThrusterRPM);
    ThrusterRPM = (1.0-coupling_sq) * ThrusterRPM  + coupling_sq * 0.02 * (EngineRPM + 49.0*ThrusterRPM);
 
    // enforce equal rpm
    if ( fabs(EngineRPM-ThrusterRPM) < 1e-3 ) {
      EngineRPM = ThrusterRPM = 0.5 * (EngineRPM+ThrusterRPM);
    }
  } else {
    d_omega = (engine_torque - ThrusterTorque)/(ThrusterMoment + EngineMoment) * dt;
    EngineRPM = ThrusterRPM += omega_to_rpm(d_omega);
  }
 
  // nothing will turn backward
  if (EngineRPM < 0.0 ) EngineRPM = 0.0;
  if (ThrusterRPM < 0.0 ) ThrusterRPM = 0.0;
 
}

◆ GetBrakeCtrlNorm()

double GetBrakeCtrlNorm ( ) const

inline

Definition at line 140 of file FGTransmission.h.

140{return BrakeCtrlNorm;}

◆ GetClutchCtrlNorm()

double GetClutchCtrlNorm ( ) const

inline

Definition at line 142 of file FGTransmission.h.

142{return ClutchCtrlNorm;}

◆ GetEngineFriction()

double GetEngineFriction ( ) const

inline

Definition at line 128 of file FGTransmission.h.

128{return EngineFriction;}

◆ GetEngineMoment()

double GetEngineMoment ( ) const

inline

Definition at line 130 of file FGTransmission.h.

130{return EngineMoment;}

◆ GetEngineRPM()

double GetEngineRPM ( )

inline

Definition at line 136 of file FGTransmission.h.

136{return EngineRPM;}

◆ GetFreeWheelTransmission()

double GetFreeWheelTransmission ( ) const

inline

Definition at line 134 of file FGTransmission.h.

134{return FreeWheelTransmission;}

◆ GetMaxBrakePower()

double GetMaxBrakePower ( ) const

inline

Definition at line 126 of file FGTransmission.h.

126{return MaxBrakePower;}

◆ GetThrusterMoment()

double GetThrusterMoment ( ) const

inline

Definition at line 132 of file FGTransmission.h.

132{return ThrusterMoment;}

◆ GetThrusterRPM()

double GetThrusterRPM ( )

inline

Definition at line 138 of file FGTransmission.h.

138{return ThrusterRPM;}

◆ ResetToIC()

void ResetToIC ( void )

Reset the initial conditions.

Definition at line 70 of file FGTransmission.cpp.

{
  InitDynamics();
  FreeWheelLag.reset();
}

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◆ SetBrakeCtrlNorm()

void SetBrakeCtrlNorm ( double x )

inline

Definition at line 141 of file FGTransmission.h.

141{BrakeCtrlNorm=x;}

◆ SetClutchCtrlNorm()

void SetClutchCtrlNorm ( double x )

inline

Definition at line 143 of file FGTransmission.h.

143{ClutchCtrlNorm=x;}

◆ SetEngineFriction()

void SetEngineFriction ( double x )

inline

Definition at line 127 of file FGTransmission.h.

127{EngineFriction=x;}

◆ SetEngineMoment()

void SetEngineMoment ( double x )

inline

Definition at line 129 of file FGTransmission.h.

129{EngineMoment=x;}

◆ SetEngineRPM()

void SetEngineRPM ( double x )

inline

Definition at line 135 of file FGTransmission.h.

135{EngineRPM=x;}

◆ SetMaxBrakePower()

void SetMaxBrakePower ( double x )

inline

Definition at line 125 of file FGTransmission.h.

125{MaxBrakePower=x;}

◆ SetThrusterMoment()

void SetThrusterMoment ( double x )

inline

Definition at line 131 of file FGTransmission.h.

131{ThrusterMoment=x;}

◆ SetThrusterRPM()

void SetThrusterRPM ( double x )

inline

Definition at line 137 of file FGTransmission.h.

137{ThrusterRPM=x;}

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

Detailed Description

Property tree

Notes

Public Member Functions

Additional Inherited Members

Constructor & Destructor Documentation

◆ FGTransmission()

◆ ~FGTransmission()

Member Function Documentation

◆ Calculate()

◆ GetBrakeCtrlNorm()

◆ GetClutchCtrlNorm()

◆ GetEngineFriction()

◆ GetEngineMoment()

◆ GetEngineRPM()

◆ GetFreeWheelTransmission()

◆ GetMaxBrakePower()

◆ GetThrusterMoment()

◆ GetThrusterRPM()

◆ ResetToIC()

◆ SetBrakeCtrlNorm()

◆ SetClutchCtrlNorm()

◆ SetEngineFriction()

◆ SetEngineMoment()

◆ SetEngineRPM()

◆ SetMaxBrakePower()

◆ SetThrusterMoment()

◆ SetThrusterRPM()