FlightGear: JSBSim::FGTrim Class Reference

The trimming routine for JSBSim. More...

#include <FGTrim.h>

Public Member Functions
	FGTrim (FGFDMExec *FDMExec, TrimMode tm=tGround)
	Initializes the trimming class.

	~FGTrim (void)

bool	DoTrim (void)
	Execute the trim.

void	Report (void)
	Print the results of the trim.

void	TrimStats ()
	Iteration statistics.

void	SetMode (TrimMode tm)
	Clear all state-control pairs and set a predefined trim mode.

void	ClearStates (void)
	Clear all state-control pairs from the current configuration.

bool	AddState (State state, Control control)
	Add a state-control pair to the current configuration.

bool	RemoveState (State state)
	Remove a specific state-control pair from the current configuration.

bool	EditState (State state, Control new_control)
	Change the control used to zero a state previously configured.

void	SetGammaFallback (bool bb)
	automatically switch to trimming longitudinal acceleration with flight path angle (gamma) once it becomes apparent that there is not enough/too much thrust.

bool	GetGammaFallback (void)
	query the fallback state

void	SetMaxCycles (int ii)
	Set the iteration limit.

void	SetMaxCyclesPerAxis (int ii)
	Set the per-axis iteration limit.

void	SetTolerance (double tt)
	Set the tolerance for declaring a state trimmed.

void	SetDebug (int level)
	Debug level 1 shows results of each top-level iteration Debug level 2 shows level 1 & results of each per-axis iteration.

void	ClearDebug (void)

void	DebugState (State state)
	Output debug data for one of the axes The State enum is defined in FGTrimAxis.h.

void	SetTargetNlf (double nlf)

double	GetTargetNlf (void)

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

virtual	~FGJSBBase ()
	Destructor for FGJSBBase.

void	PutMessage (const Message &msg)
	Places a Message structure on the Message queue.

void	PutMessage (const std::string &text)
	Creates a message with the given text and places it on the queue.

void	PutMessage (const std::string &text, bool bVal)
	Creates a message with the given text and boolean value and places it on the queue.

void	PutMessage (const std::string &text, int iVal)
	Creates a message with the given text and integer value and places it on the queue.

void	PutMessage (const std::string &text, double dVal)
	Creates a message with the given text and double value and places it on the queue.

int	SomeMessages (void) const
	Reads the message on the queue (but does not delete it).

void	ProcessMessage (void)
	Reads the message on the queue and removes it from the queue.

Message *	ProcessNextMessage (void)
	Reads the next message on the queue and removes it from the queue.

void	disableHighLighting (void)
	Disables highlighting in the console output.

Additional Inherited Members
Public Types inherited from JSBSim::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 const std::string &	GetVersion (void)
	Returns the version number of JSBSim.

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

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

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

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

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

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

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

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

static double	PitotTotalPressure (double mach, double p)
	Compute the total pressure in front of the Pitot tube.

static double	MachFromImpactPressure (double qc, double p)
	Compute the Mach number from the differential pressure (qc) and the static pressure.

static double	VcalibratedFromMach (double mach, double p)
	Calculate the calibrated airspeed from the Mach number.

static double	MachFromVcalibrated (double vcas, double p)
	Calculate the Mach number from the calibrated airspeed.Based on the formulas in the US Air Force Aircraft Performance Flight Testing Manual (AFFTC-TIH-99-01).

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

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

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

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

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)

static double	GaussianRandomNumber (void)

Static Public Attributes inherited from JSBSim::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 std::string	CreateIndexedPropertyName (const std::string &Property, int index)

static Message	localMsg

static std::queue< Message >	Messages

static unsigned int	messageId = 0

static constexpr double	radtodeg = 180. / 3.14159265358979323846

static constexpr double	degtorad = 3.14159265358979323846 / 180.

static constexpr double	hptoftlbssec = 550.0

static constexpr double	psftoinhg = 0.014138

static constexpr double	psftopa = 47.88

static constexpr double	ktstofps = 1.68781

static constexpr double	fpstokts = 1.0 / ktstofps

static constexpr double	inchtoft = 1.0/12.0

static constexpr double	fttom = 0.3048

static constexpr double	m3toft3 = 1.0/(fttomfttomfttom)

static constexpr double	in3tom3 = inchtoftinchtoftinchtoft/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.

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__

static int	gaussian_random_number_phase = 0

Detailed Description

The trimming routine for JSBSim.

FGTrim finds the aircraft attitude and control settings needed to maintain the steady state described by the FGInitialCondition object . It does this iteratively by assigning a control to each state and adjusting that control until the state is within a specified tolerance of zero. States include the recti-linear accelerations udot, vdot, and wdot, the angular accelerations qdot, pdot, and rdot, and the difference between heading and ground track. Controls include the usual flight deck controls available to the pilot plus angle of attack (alpha), sideslip angle(beta), flight path angle (gamma), pitch attitude(theta), roll attitude(phi), and altitude above ground. The last three are used for on-ground trimming. The state-control pairs used in a given trim are completely user configurable and several pre-defined modes are provided as well. They are:

tLongitudinal: Trim wdot with alpha, udot with thrust, qdot with elevator
tFull: tLongitudinal + vdot with phi, pdot with aileron, rdot with rudder and heading minus ground track (hmgt) with beta
tPullup: tLongitudinal but adjust alpha to achieve load factor input with SetTargetNlf()
tGround: wdot with altitude, qdot with theta, and pdot with phi

The remaining modes include tCustom, which is completely user defined and tNone.

Note that trims can (and do) fail for reasons that are completely outside the control of the trimming routine itself. The most common problem is the initial conditions: is the model capable of steady state flight at those conditions? Check the speed, altitude, configuration (flaps, gear, etc.), weight, cg, and anything else that may be relevant.

Example usage:

FGFDMExec* FDMExec = new FGFDMExec();
 
FGInitialCondition* fgic = new FGInitialCondition(FDMExec);
FGTrim fgt(FDMExec, fgic, tFull);
fgic->SetVcaibratedKtsIC(100);
fgic->SetAltitudeFtIC(1000);
fgic->SetClimbRate(500);
if( !fgt.DoTrim() ) {
  cout << "Trim Failed" << endl;
}
fgt.Report();

Author: Tony Peden

Definition at line 123 of file FGTrim.h.

Constructor & Destructor Documentation

◆ FGTrim()

JSBSim::FGTrim::FGTrim	(	FGFDMExec *	FDMExec,
		TrimMode	tm = tGround )

Initializes the trimming class.

Parameters

FDMExec	pointer to a JSBSim executive object.
tm	trim mode

Definition at line 61 of file FGTrim.cpp.

◆ ~FGTrim()

JSBSim::FGTrim::~FGTrim ( void )

Definition at line 86 of file FGTrim.cpp.

Member Function Documentation

◆ AddState()

bool JSBSim::FGTrim::AddState	(	State	state,
		Control	control )

Add a state-control pair to the current configuration.

See the enums State and Control in FGTrimAxis.h for the available options. Will fail if the given state is already configured.

Parameters

state	the accel or other condition to zero
control	the control used to zero the state

Returns: true if add is successful

Definition at line 130 of file FGTrim.cpp.

◆ ClearDebug()

void JSBSim::FGTrim::ClearDebug ( void )

inline

Definition at line 280 of file FGTrim.h.

◆ ClearStates()

void JSBSim::FGTrim::ClearStates ( void )

Clear all state-control pairs from the current configuration.

The trimming routine must have at least one state-control pair configured to be useful

Definition at line 122 of file FGTrim.cpp.

◆ DebugState()

void JSBSim::FGTrim::DebugState ( State state )

inline

Output debug data for one of the axes The State enum is defined in FGTrimAxis.h.

Definition at line 286 of file FGTrim.h.

◆ DoTrim()

bool JSBSim::FGTrim::DoTrim ( void )

Execute the trim.

Definition at line 186 of file FGTrim.cpp.

◆ EditState()

bool JSBSim::FGTrim::EditState	(	State	state,
		Control	new_control )

Change the control used to zero a state previously configured.

Parameters

state	the accel or other condition to zero
new_control	the control used to zero the state

Definition at line 171 of file FGTrim.cpp.

◆ GetGammaFallback()

bool JSBSim::FGTrim::GetGammaFallback ( void )

inline

query the fallback state

Returns: true if fallback is enabled.

Definition at line 249 of file FGTrim.h.

◆ GetTargetNlf()

double JSBSim::FGTrim::GetTargetNlf ( void )

inline

Definition at line 289 of file FGTrim.h.

◆ RemoveState()

bool JSBSim::FGTrim::RemoveState ( State state )

Remove a specific state-control pair from the current configuration.

Parameters

state the state to remove

Returns: true if removal is successful

Definition at line 148 of file FGTrim.cpp.

◆ Report()

void JSBSim::FGTrim::Report ( void )

Print the results of the trim.

For each axis trimmed, this includes the final state value, control value, and tolerance used.

Returns: true if trim succeeds

Definition at line 113 of file FGTrim.cpp.

◆ SetDebug()

void JSBSim::FGTrim::SetDebug ( int level )

inline

Debug level 1 shows results of each top-level iteration Debug level 2 shows level 1 & results of each per-axis iteration.

Definition at line 279 of file FGTrim.h.

◆ SetGammaFallback()

void JSBSim::FGTrim::SetGammaFallback ( bool bb )

inline

automatically switch to trimming longitudinal acceleration with flight path angle (gamma) once it becomes apparent that there is not enough/too much thrust.

Parameters

bb	true to enable fallback

Definition at line 244 of file FGTrim.h.

◆ SetMaxCycles()

void JSBSim::FGTrim::SetMaxCycles ( int ii )

inline

Set the iteration limit.

DoTrim() will return false if limit iterations are reached before trim is achieved. The default is 60. This does not ordinarily need to be changed.

Parameters

ii	integer iteration limit

Definition at line 256 of file FGTrim.h.

◆ SetMaxCyclesPerAxis()

void JSBSim::FGTrim::SetMaxCyclesPerAxis ( int ii )

inline

Set the per-axis iteration limit.

Attempt to zero each state by iterating limit times before moving on to the next. The default limit is 100 and also does not ordinarily need to be changed.

Parameters

ii	integer iteration limit

Definition at line 264 of file FGTrim.h.

◆ SetMode()

void JSBSim::FGTrim::SetMode ( TrimMode tm )

Clear all state-control pairs and set a predefined trim mode.

Parameters

tm	the set of axes to trim. Can be: tLongitudinal, tFull, tGround, tCustom, or tNone

Definition at line 800 of file FGTrim.cpp.

◆ SetTargetNlf()

void JSBSim::FGTrim::SetTargetNlf ( double nlf )

inline

Definition at line 288 of file FGTrim.h.

◆ SetTolerance()

void JSBSim::FGTrim::SetTolerance ( double tt )

inline

Set the tolerance for declaring a state trimmed.

Angular accels are held to a tolerance of 1/10th of the given. The default is 0.001 for the recti-linear accelerations and 0.0001 for the angular.

Definition at line 270 of file FGTrim.h.

◆ TrimStats()

void JSBSim::FGTrim::TrimStats ( )

Iteration statistics.

Definition at line 92 of file FGTrim.cpp.

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

Public Member Functions

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ FGTrim()

◆ ~FGTrim()

Member Function Documentation

◆ AddState()

◆ ClearDebug()

◆ ClearStates()

◆ DebugState()

◆ DoTrim()

◆ EditState()

◆ GetGammaFallback()

◆ GetTargetNlf()

◆ RemoveState()

◆ Report()

◆ SetDebug()

◆ SetGammaFallback()

◆ SetMaxCycles()

◆ SetMaxCyclesPerAxis()

◆ SetMode()

◆ SetTargetNlf()

◆ SetTolerance()

◆ TrimStats()