Detailed Description

Encapsulates code that models an individual arbitrary force, moment or a combination thereof.

This class encapsulates an individual reaction applied at the specified location on the vehicle, and oriented as specified in one of three frames:

BODY frame is defined with the X axis positive forward, the Y axis positive out the right wing, and the Z axis completing the set positive downward out the belly of the aircraft.
LOCAL frame is a world-based frame, with X positive north, Y positive east and Z completing the right handed system positive down towards the center of the Earth.
WIND frame (rotated) has X negative into the wind vector (in other words drag is along the positive X axis), the Z axis is perpendicular to X and positive up (lift) but in the aircraft XZ plane, and Y completes the right handed system. This is modified from a normal wind frame definition, which is rotated about the Y axis 180 degrees from this WIND frame.
INERTIAL frame refers to the ECI frame.

Much of the substance of this class is located in the FGForce base class, from which this class is derived.

Here is the XML definition of a force (optional items are in []):

<force name="name" frame="BODY | LOCAL | WIND">
 
  [<function> ... </function>]
 
  <location unit="{IN | M}"> 
    <x> {number} </x>
    <y> {number} </y>
    <z> {number} </z>
  </location>
  [<direction> <!-- optional initial direction vector -->
    <x> {number} </x>
    <y> {number} </y>
    <z> {number} </z>
  </direction>]
</force>

The location of the force vector, in structural coordinates, can be set at runtime through the following properties:

external_reactions/{force name}/location-x-in
external_reactions/{force name}/location-y-in
external_reactions/{force name}/location-z-in

The XML definition of a moment (optional items are in []) is a bit simpler because you do not need to specify the location:

<moment name="name" frame="BODY | LOCAL | WIND">
 
  [<function> ... </function>]
 
  [<direction> <!-- optional initial direction vector -->
    <x> {number} </x>
    <y> {number} </y>
    <z> {number} </z>
  </direction>]
</moment>

The initial direction can optionally be set by specifying a unit vector in the chosen frame (body, local, or wind).

As an example, a parachute can be defined oriented in the wind axis frame so the drag always acts in the drag direction - opposite the positive X axis. That does not include the effects of parachute oscillations, but those could be handled in the calling application.

The force (or moment) direction is not actually required to be specified as a unit vector, but prior to the force (or moment) vector being calculated, the direction vector is normalized when initialized.

The force direction can be specified at runtime through setting any/all of the following properties:

external_reactions/{force name}/x
external_reactions/{force name}/y
external_reactions/{force name}/z

The moment direction can be specified at runtime through setting any/all of the following properties:

external_reactions/{moment name}/l
external_reactions/{moment name}/m
external_reactions/{moment name}/n

However in that case, the direction is no longer normalized.

When no <function> has been provided in the force definition, its magnitude can be specified through the following property:

external_reactions/{force name}/magnitude

When no <function> has been provided in the moment definition, its magnitude can be specified through the following property:

external_reactions/{moment name}/magnitude-lbsft

Definition at line 211 of file FGExternalForce.h.

#include <FGExternalForce.h>

Inheritance diagram for FGExternalForce:

Collaboration diagram for FGExternalForce:

Public Member Functions
	FGExternalForce (const FGExternalForce &extForce)
	Copy Constructor.

	FGExternalForce (FGFDMExec *FDMExec)
	Constructor.

	~FGExternalForce () override
	Destructor.

const FGColumnVector3 &	GetBodyForces (void) override

void	setForce (Element *el)

void	setMoment (Element *el)

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

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.

void	SetActingLocationX (double x)

void	SetActingLocationY (double y)

void	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 FGForce
enum	TransformType { tNone , tWindBody , tLocalBody , tInertialBody , tCustom }

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 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 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 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 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/(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__

Constructor & Destructor Documentation

◆ FGExternalForce() [1/2]

FGExternalForce ( FGFDMExec * FDMExec )

inlineexplicit

Constructor.

Parameters

FDMExec	pointer to the main executive class.
el	pointer to the XML element defining an individual force.

Definition at line 218 of file FGExternalForce.h.

219 : FGForce(FDMExec), forceMagnitude(NULL), momentMagnitude(NULL)

220 { Debug(0); }

JSBSim::FGForce::FGForce

FGForce(FGFDMExec *FDMExec)

Constructor.

Definition FGForce.cpp:52

◆ FGExternalForce() [2/2]

FGExternalForce ( const FGExternalForce & extForce )

Copy Constructor.

Parameters

extForce a reference to an existing FGExternalForce object

◆ ~FGExternalForce()

~FGExternalForce ( )

override

Destructor.

Definition at line 187 of file FGExternalForce.cpp.

{
  delete forceMagnitude;
  delete momentMagnitude;
  Debug(1);
}

Member Function Documentation

◆ GetBodyForces()

const FGColumnVector3 & GetBodyForces ( void )

overridevirtual

Reimplemented from FGForce.

Definition at line 196 of file FGExternalForce.cpp.

{
  if (forceMagnitude)
    vFn = forceMagnitude->GetValue() * forceDirection;
 
  if (momentMagnitude)
    vMn = Transform() * (momentMagnitude->GetValue() * momentDirection);
 
  return FGForce::GetBodyForces();
}

◆ setForce()

void setForce ( Element * el )

Definition at line 145 of file FGExternalForce.cpp.

{
  auto PropertyManager = fdmex->GetPropertyManager();
  Name = el->GetAttributeValue("name");
  string BasePropertyName = "external_reactions/" + Name;
 
  forceDirection = FGPropertyVector3(PropertyManager.get(), BasePropertyName,
                                     "x", "y", "z");
  forceMagnitude = bind(el, BasePropertyName + "/magnitude", forceDirection);
 
  Element* location_element = el->FindElement("location");
  if (!location_element) {
    cerr << el->ReadFrom()
         << "No location element specified in force object." << endl;
  } else {
    FGColumnVector3 location = location_element->FindElementTripletConvertTo("IN");
    SetLocation(location);
  }
  PropertyManager->Tie( BasePropertyName + "/location-x-in", (FGForce*)this,
                        &FGForce::GetLocationX, &FGForce::SetLocationX);
  PropertyManager->Tie( BasePropertyName + "/location-y-in", (FGForce*)this,
                        &FGForce::GetLocationY, &FGForce::SetLocationY);
  PropertyManager->Tie( BasePropertyName + "/location-z-in", (FGForce*)this,
                        &FGForce::GetLocationZ, &FGForce::SetLocationZ);
}

◆ setMoment()

void setMoment ( Element * el )

Definition at line 173 of file FGExternalForce.cpp.

{
  auto PropertyManager = fdmex->GetPropertyManager();
  Name = el->GetAttributeValue("name");
  string BasePropertyName = "external_reactions/" + Name;
 
  momentDirection = FGPropertyVector3(PropertyManager.get(), BasePropertyName,
                                      "l", "m", "n");
  momentMagnitude = bind(el, BasePropertyName + "/magnitude-lbsft",
                         momentDirection);
}

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