Detailed Description

Models a generic rocket engine.

The rocket engine is modeled given the following parameters:

Specific Impulse (in sec)

Additionally, the following control inputs, operating characteristics, and location are required, as with all other engine types:

Throttle setting (in percent, from 0 to 1.0)
Maximum allowable throttle setting
Minimum working throttle setting
Sea level fuel flow at maximum thrust
Sea level oxidizer flow at maximum thrust
X, Y, Z location in structural coordinate frame
Pitch and Yaw

The nozzle exit pressure (p2) is returned via a call to FGNozzle::GetPowerRequired(). This exit pressure is used to get the at-altitude thrust level.

One can model the thrust of a solid rocket by providing a normalized thrust table as a function of time. For instance, the space shuttle solid rocket booster normalized thrust value looks roughly like this:

    
 <thrust_table name="propulsion/thrust_time" type="internal">
   <tableData>
      0.0   0.00
      0.2   0.91
      8.0   0.97
     16.0   0.99
     20.0   1.00
     21.0   1.00
     24.0   0.95
     32.0   0.85
     40.0   0.78
     48.0   0.72
     50.0   0.71
     52.0   0.71
     56.0   0.73
     64.0   0.78
     72.0   0.82
     80.0   0.81
     88.0   0.73
     96.0   0.69
    104.0   0.59
    112.0   0.46
    120.0   0.09
    132.0   0.00
   </tableData>
 </thrust_table>

T
he left column is time, the right column is normalized thrust. Inside the FGRocket class code, the maximum thrust is calculated, and multiplied by this table. The Rocket class also tracks burn time. All that needs to be done is for the rocket engine to be throttle up to 1. At that time, the solid rocket fuel begins burning and thrust is provided.

@author Jon S. Berndt
@see FGNozzle,
FGThruster,
FGForce,
FGEngine,

Definition at line 125 of file FGRocket.h.

#include <FGRocket.h>

Inheritance diagram for FGRocket:

Collaboration diagram for FGRocket:

Public Member Functions
	FGRocket (FGFDMExec exec, Element el, int engine_number, struct FGEngine::Inputs &input)
	Constructor. More...

	~FGRocket (void)
	Destructor.

double	CalcFuelNeed (void)
	The fuel need is calculated based on power levels and flow rate for that power level. More...

double	CalcOxidizerNeed (void)
	The oxidizer need is calculated based on power levels and flow rate for that power level. More...

void	Calculate (void)
	Determines the thrust.

std::string	GetEngineLabels (const std::string &delimiter)

std::string	GetEngineValues (const std::string &delimiter)

bool	GetFlameout (void)
	Gets the flame-out status. More...

double	GetIsp (void) const

double	GetMixtureRatio (void) const

double	GetOxiFlowRate (void) const

double	GetThrustVariation (void) const
	Returns the thrust variation, if any.

double	GetTotalImpulse (void) const
	Gets the total impulse of the rocket. More...

double	GetTotalIspVariation (void) const
	Returns the Total Isp variation, if any.

double	GetVacTotalImpulse (void) const
	Gets the total impulse of the rocket. More...

void	SetIsp (double isp)

void	SetMixtureRatio (double mix)

void	SetThrustVariation (double var)
	Sets the thrust variation for a solid rocket engine. More...

void	SetTotalIspVariation (double var)
	Sets the variation in total motor energy. More...

Public Member Functions inherited from FGEngine
	FGEngine (int engine_number, struct Inputs &input)

virtual const FGColumnVector3 &	GetBodyForces (void)

virtual bool	GetCranking (void) const

virtual double	getFuelFlow_gph () const

virtual double	getFuelFlow_pph () const

virtual double	GetFuelFlowRate (void) const

virtual double	GetFuelFlowRateGPH (void) const

virtual double	GetFuelUsedLbs (void) const

virtual const FGColumnVector3 &	GetMoments (void)

virtual const std::string &	GetName (void) const

size_t	GetNumSourceTanks () const

virtual double	GetPowerAvailable (void)

virtual bool	GetRunning (void) const

unsigned int	GetSourceTank (unsigned int i) const

virtual bool	GetStarter (void) const

virtual bool	GetStarved (void) const

virtual double	GetThrottleMax (void) const

virtual double	GetThrottleMin (void) const

virtual double	GetThrust (void) const

FGThruster *	GetThruster (void) const

EngineType	GetType (void) const

virtual int	InitRunning (void)

void	LoadThruster (FGFDMExec exec, Element el)

void	LoadThrusterInputs ()

virtual void	ResetToIC (void)
	Resets the Engine parameters to the initial conditions.

virtual void	SetFuelDensity (double d)

virtual void	SetFuelFreeze (bool f)

virtual void	SetName (const std::string &name)

virtual void	SetRunning (bool bb)

virtual void	SetStarter (bool s)

virtual void	SetStarved (bool tt)

virtual void	SetStarved (void)

Public Member Functions inherited from FGModelFunctions
std::string	GetFunctionStrings (const std::string &delimeter) const
	Gets the strings for the current set of functions. More...

std::string	GetFunctionValues (const std::string &delimeter) const
	Gets the function values. More...

std::shared_ptr< FGFunction >	GetPreFunction (const std::string &name)
	Get one of the "pre" function. More...

bool	Load (Element el, FGFDMExec fdmex, std::string prefix="")

void	PostLoad (Element el, FGFDMExec fdmex, std::string prefix="")

void	PreLoad (Element el, FGFDMExec fdmex, std::string prefix="")

void	RunPostFunctions (void)

void	RunPreFunctions (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 FGEngine
enum	EngineType { etUnknown , etRocket , etPiston , etTurbine , etTurboprop , etElectric }

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 FGEngine
struct 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

Protected Member Functions inherited from FGEngine
void	Debug (int from)

bool	Load (FGFDMExec exec, Element el)

Protected Member Functions inherited from FGModelFunctions
virtual bool	InitModel (void)

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

Protected Attributes inherited from FGEngine
bool	Cranking

const int	EngineNumber

double	FuelDensity

double	FuelExpended

double	FuelFlow_gph

double	FuelFlow_pph

double	FuelFlowRate

bool	FuelFreeze

double	FuelUsedLbs

double	MaxThrottle

double	MinThrottle

std::string	Name

double	PctPower

bool	Running

double	SLFuelFlowMax

std::vector< int >	SourceTanks

bool	Starter

bool	Starved

FGThruster *	Thruster

EngineType	Type

Protected Attributes inherited from FGModelFunctions
FGPropertyReader	LocalProperties

std::vector< std::shared_ptr< FGFunction > >	PostFunctions

std::vector< std::shared_ptr< FGFunction > >	PreFunctions

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. 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

◆ FGRocket()

FGRocket	(	FGFDMExec *	exec,
		Element *	el,
		int	engine_number,
		struct FGEngine::Inputs &	input
	)

Constructor.

Parameters

exec	pointer to JSBSim parent object, the FDM Executive.
el	a pointer to the XML Element instance representing the engine.
engine_number	engine number

Definition at line 54 of file FGRocket.cpp.

   : FGEngine(engine_number, input), isp_function(nullptr), FDMExec(exec)
 {
   Load(exec, el);
  
   Type = etRocket;
   Element* thrust_table_element = nullptr;
   ThrustTable = nullptr;
   BurnTime = 0.0;
   previousFuelNeedPerTank = 0.0;
   previousOxiNeedPerTank = 0.0;
   PropellantFlowRate = 0.0;
   TotalPropellantExpended = 0.0;
   FuelFlowRate = FuelExpended = 0.0;
   OxidizerFlowRate = OxidizerExpended = 0.0;
   SLOxiFlowMax = SLFuelFlowMax = PropFlowMax = 0.0;
   MxR = 0.0;
   BuildupTime = 0.0;
   It = ItVac = 0.0;
   ThrustVariation = 0.0;
   TotalIspVariation = 0.0;
   VacThrust = 0.0;
   Flameout = false;
  
   // Defaults
    MinThrottle = 0.0;
    MaxThrottle = 1.0;
  
   std::stringstream strEngineNumber;
   strEngineNumber << EngineNumber;
  
   auto PropertyManager = exec->GetPropertyManager();
   bindmodel(PropertyManager.get()); // Bind model properties first, since they might be needed in functions.
  
   Element* isp_el = el->FindElement("isp");
  
   // Specific impulse may be specified as a constant value or as a function -
   // perhaps as a function of mixture ratio.
   if (isp_el) {
     Element* isp_func_el = isp_el->FindElement("function");
     if (isp_func_el) {
       isp_function = new FGFunction(exec, isp_func_el, strEngineNumber.str());
     } else {
       Isp = el->FindElementValueAsNumber("isp");
     }
   } else {
     throw("Specific Impulse <isp> must be specified for a rocket engine");
   }
   
   if (el->FindElement("builduptime"))
     BuildupTime = el->FindElementValueAsNumber("builduptime");
   if (el->FindElement("maxthrottle"))
     MaxThrottle = el->FindElementValueAsNumber("maxthrottle");
   if (el->FindElement("minthrottle"))
     MinThrottle = el->FindElementValueAsNumber("minthrottle");
  
   if (el->FindElement("slfuelflowmax")) {
     SLFuelFlowMax = el->FindElementValueAsNumberConvertTo("slfuelflowmax", "LBS/SEC");
     if (el->FindElement("sloxiflowmax")) {
     SLOxiFlowMax = el->FindElementValueAsNumberConvertTo("sloxiflowmax", "LBS/SEC");
     }
     PropFlowMax = SLOxiFlowMax + SLFuelFlowMax;
     MxR = SLOxiFlowMax/SLFuelFlowMax;
   } else if (el->FindElement("propflowmax")) {
     PropFlowMax = el->FindElementValueAsNumberConvertTo("propflowmax", "LBS/SEC");
     // Mixture ratio may be specified here, but it can also be specified as a
     // function or via property
     if (el->FindElement("mixtureratio")) {
       MxR = el->FindElementValueAsNumber("mixtureratio");
     }
   }
  
   if (isp_function) Isp = isp_function->GetValue(); // cause Isp function to be executed if present.
   // If there is a thrust table element, this is a solid propellant engine.
   thrust_table_element = el->FindElement("thrust_table");
   if (thrust_table_element) {
     ThrustTable = new FGTable(PropertyManager, thrust_table_element);
     Element* variation_element = el->FindElement("variation");
     if (variation_element) {
       if (variation_element->FindElement("thrust")) {
         ThrustVariation = variation_element->FindElementValueAsNumber("thrust");
       }
       if (variation_element->FindElement("total_isp")) {
         TotalIspVariation = variation_element->FindElementValueAsNumber("total_isp");
       }
     }
   }
  
  
   Debug(0);
 }

Here is the call graph for this function:

Member Function Documentation

◆ CalcFuelNeed()

double CalcFuelNeed ( void )

virtual

The fuel need is calculated based on power levels and flow rate for that power level.

It is also turned from a rate into an actual amount (pounds) by multiplying it by the delta T and the rate.

Returns: Total fuel requirement for this engine in pounds.

Reimplemented from FGEngine.

Definition at line 222 of file FGRocket.cpp.

 {
   if (ThrustTable != 0L) {          // Thrust table given - infers solid fuel
     FuelFlowRate = VacThrust/Isp;   // This calculates wdot (weight flow rate in lbs/sec)
     FuelFlowRate /= (1 + TotalIspVariation);
   } else {
     SLFuelFlowMax = PropFlowMax / (1 + MxR);
     FuelFlowRate = SLFuelFlowMax * PctPower;
   }
  
   FuelExpended = FuelFlowRate * in.TotalDeltaT; // For this time step ...
   return FuelExpended;
 }

◆ CalcOxidizerNeed()

double CalcOxidizerNeed ( void )

virtual

The oxidizer need is calculated based on power levels and flow rate for that power level.

It is also turned from a rate into an actual amount (pounds) by multiplying it by the delta T and the rate.

Returns: Total oxidizer requirement for this engine in pounds.

Reimplemented from FGEngine.

Definition at line 238 of file FGRocket.cpp.

 {
   SLOxiFlowMax = PropFlowMax * MxR / (1 + MxR);
   OxidizerFlowRate = SLOxiFlowMax * PctPower;
   OxidizerExpended = OxidizerFlowRate * in.TotalDeltaT;
   return OxidizerExpended;
 }

◆ GetFlameout()

bool GetFlameout ( void )

inline

Gets the flame-out status.

The engine will "flame out" if the throttle is set below the minimum sustainable-thrust setting.

Returns: true if engine has flamed out.

Definition at line 164 of file FGRocket.h.

164 {return Flameout;}

◆ GetTotalImpulse()

double GetTotalImpulse ( void ) const

inline

Gets the total impulse of the rocket.

Returns: The cumulative actual total impulse of the rocket up to this time.

Definition at line 154 of file FGRocket.h.

154 {return It;}

◆ GetVacTotalImpulse()

double GetVacTotalImpulse ( void ) const

inline

Gets the total impulse of the rocket.

Returns: The cumulative vacuum total impulse of the rocket up to this time.

Definition at line 158 of file FGRocket.h.

158 {return ItVac;}

◆ SetThrustVariation()

void SetThrustVariation ( double var )

inline

Sets the thrust variation for a solid rocket engine.

Solid propellant rocket motor thrust characteristics are typically defined at 70 degrees F temperature. At any other temperature, performance will be different. Warmer propellant grain will burn quicker and at higher thrust. Total motor impulse is not changed for change in thrust.

Parameters

var	the variation in percent. That is, a 2 percent variation would be specified as 0.02. A positive 2% variation in thrust would increase the thrust by 2%, and shorten the burn time.

Definition at line 188 of file FGRocket.h.

188 {ThrustVariation = var;}

◆ SetTotalIspVariation()

void SetTotalIspVariation ( double var )

inline

Sets the variation in total motor energy.

The total energy present in a solid rocket motor can be modified (such as might happen with manufacturing variations) by setting the total Isp variation.

Parameters

var	the variation in percent. That is, a 2 percent variation would be specified as 0.02. This variation will affect the total thrust, but not the burn time.

Definition at line 197 of file FGRocket.h.

197 {TotalIspVariation = var;}

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

Detailed Description

Public Member Functions

Additional Inherited Members

Constructor & Destructor Documentation

◆ FGRocket()

Member Function Documentation

◆ CalcFuelNeed()

◆ CalcOxidizerNeed()

◆ GetFlameout()

◆ GetTotalImpulse()

◆ GetVacTotalImpulse()

◆ SetThrustVariation()

◆ SetTotalIspVariation()