FGPiston Class Reference

Detailed Description

Models a Supercharged Piston engine.

Based on Dave Luff's model.

Configuration File Format:

<piston_engine name="{string}">
  <minmp unit="{INHG | PA | ATM}"> {number} </minmp>
  <maxmp unit="{INHG | PA | ATM}"> {number} </maxmp>
  <idlerpm> {number} </idlerpm>
  <maxrpm> {number} </maxrpm>
  <maxhp unit="{HP | WATTS}"> {number} </maxhp>
  <displacement unit="{IN3 | LTR | CC}"> {number} </displacement>
  <cycles> {number} </cycles>
  <bore unit="{IN | M}"> {number} </bore>
  <stroke unit="{IN | M}"> {number} </stroke>
  <cylinders> {number} </cylinders>
  <compression-ratio> {number} </compression-ratio>
  <sparkfaildrop> {number} </sparkfaildrop>
  <static-friction unit="{HP | WATTS}"> {number} </static-friction>
  <air-intake-impedance-factor> {number} </air-intake-impedance-factor>
  <ram-air-factor> {number} </ram-air-factor>
  <cooling-factor> {number} </cooling-factor>
  <man-press-lag> {number} </man-press-lag>
  <starter-torque> {number} </starter-torque> 
  <starter-rpm> {number} </starter-rpm> 
  <cylinder-head-mass unit="{KG | LBS}"> {number} </cylinder-head-mass>
  <bsfc unit="{LBS/HP*HR | "KG/KW*HR"}"> {number} </bsfc>
  <volumetric-efficiency> {number} </volumetric-efficiency>
  <dynamic-fmep unit="{INHG | PA | ATM}"> {number} </dynamic-fmep>
  <static-fmep unit="{INHG | PA | ATM}"> {number} </static-fmep>
  <numboostspeeds> {number} </numboostspeeds>
  <boostoverride> {0 | 1} </boostoverride>
  <boostmanual> {0 | 1} </boostmanual>
  <boost-loss-factor> {number} </boost-loss-factor>
  <ratedboost1 unit="{INHG | PA | ATM}"> {number} </ratedboost1>
  <ratedpower1 unit="{HP | WATTS}"> {number} </ratedpower1>
  <ratedrpm1> {number} </ratedrpm1>
  <ratedaltitude1 unit="{FT | M}"> {number} </ratedaltitude1>
  <ratedboost2 unit="{INHG | PA | ATM}"> {number} </ratedboost2>
  <ratedpower2 unit="{HP | WATTS}"> {number} </ratedpower2>
  <ratedrpm2> {number} </ratedrpm2>
  <ratedaltitude2 unit="{FT | M}"> {number} </ratedaltitude2>
  <ratedboost3 unit="{INHG | PA | ATM}"> {number} </ratedboost3>
  <ratedpower3 unit="{HP | WATTS}"> {number} </ratedpower3>
  <ratedrpm3> {number} </ratedrpm3>
  <ratedaltitude3 unit="{FT | M}"> {number} </ratedaltitude3>
  <takeoffboost unit="{INHG | PA | ATM}"> {number} </takeoffboost>
  <oil-pressure-relief-valve-psi> {number} </oil-pressure-relief-valve=psi>
  <design-oil-temp-degK>  {number} </design-oil-temp-degK>
  <oil-pressure-rpm-max> {number} </oil-pressure-rpm-max>
  <oil-viscosity-index> {number} </oil-viscosity-index>
</piston_engine>

Definition of the piston engine configuration file parameters:

Basic parameters:

• minmp - this value is the nominal idle manifold pressure at sea-level without boost. Along with idlerpm, it determines throttle response slope.
• maxmp - this value is the nominal maximum manifold pressure at sea-level without boost. Along with maxrpm it determines the resistance of the aircraft intake system. Overridden by air-intake-impedance-factor
• man-press-lag - Delay in seconds for manifold pressure changes to take effect
• starter-torque - A value specifing the zero RPM torque in lb*ft the starter motor provides. Current default value is 40% of the horse power value.
• starter-rpm - A value specifing the maximum RPM the unloaded starter motor can achieve. Loads placed on the engine by the propeller and throttle will further limit RPM achieved in practice.
• idlerpm - this value affects the throttle fall off and the engine stops running if it is slowed below 80% of this value. The engine starts running when it reaches 80% of this value.
• maxrpm - this value is used to calculate air-box resistance and BSFC. It also affects oil pressure among other things.
• maxhp - this value is the nominal power the engine creates at maxrpm. It will determine bsfc if that tag is not input. It also determines the starter motor power.
• displacement - this value is used to determine mass air and fuel flow which impacts engine power and cooling.
• cycles - Designate a 2 or 4 stroke engine. Currently only the 4 stroke engine is supported.
• bore - cylinder bore is currently unused.
• stroke - piston stroke is used to determine the mean piston speed. Longer strokes result in an engine that does not work as well at higher RPMs.
• compression-ratio - the compression ratio affects the change in volumetric efficiency with altitude.
• sparkfaildrop - this is the percentage drop in horsepower for single magneto operation.
• static-friction - this value is the power required to turn an engine that is not running. Used to control and slow a windmilling propeller. Choose a small percentage of maxhp.

Advanced parameters

• bsfc - Indicated Specific Fuel Consumption. The power produced per unit of fuel. Higher numbers give worse fuel economy. This number may need to be lowered slightly from actual BSFC numbers because some internal engine losses are modeled separately. Typically between 0.3 and 0.5
• volumetric-efficiency - the nominal volumetric efficiency of the engine. This is the primary way to control fuel flow Boosted engines may require values above 1. Typical engines are 0.80 to 0.82
• air-intake-impedance-factor - this number is the pressure drop across the intake system. Increasing it reduces available manifold pressure. Also a property for run-time adjustment.
• ram-air-factor - this number creates increases manifold pressure with an increase in dynamic pressure (aircraft speed). Also a property for run-time adjustment.

Cooling control:

• cylinders - number of cylinders scales the cylinder head mass.
• cylinder-head-mass - the nominal mass of a cylinder head. A larger value slows changes in engine temperature
• cooling-factor - this number models the efficiency of the aircraft cooling system. Also a property for run-time adjustment.

Supercharge parameters:

• numboostspeed - zero (or not present) for a naturally-aspirated engine, either 1, 2 or 3 for a boosted engine. This corresponds to the number of supercharger speeds. Merlin XII had 1 speed, Merlin 61 had 2, a late Griffon engine apparently had 3. No known engine more than 3, although some German engines had continuously variable-speed superchargers.
• boostoverride - whether or not to clip output to the wastegate value
• boost-loss-factor - zero (or not present) for 'free' supercharging. A value entered will be used as a multiplier to the power required to compress the input air. Typical value should be 1.15 to 1.20.
• boostmanual - whether a multispeed supercharger will manually or automatically shift boost speeds. On manual shifting the boost speeds is accomplished by controlling the property propulsion/engine/boostspeed.

• takeoffboost - boost in psi above sea level ambient. Typically used for takeoff, and emergency situations, generally for not more than five minutes. This is a change in the boost control setting, not the actual supercharger speed, and so would only give extra power below the rated altitude. A typical takeoff boost for an early Merlin was about 12psi, compared with a rated boost of 9psi.

  When TAKEOFFBOOST is specified in the config file (and is above RATEDBOOST1), the throttle position is interpreted as:

  • 0 to 0.98 : idle manifold pressure to rated boost (where attainable)
  • 0.99, 1.0 : takeoff boost (where attainable).

The next items are all appended with either 1, 2 or 3 depending on which boostspeed they refer to:

• ratedboost[123] - the absolute rated boost above sea level ambient (14.7 PSI, 29.92 inHg) for a given boost speed.
• ratedpower[123] - unused
• ratedrpm[123] - The rpm at which rated boost is developed

• ratedaltitude[123] - The altitude up to which the rated boost can be maintained. Up to this altitude the boost is clipped to rated boost or takeoffboost. Beyond this altitude the manifold pressure must drop, since the supercharger is now at maximum unregulated output. The actual pressure multiplier of the supercharger system is calculated at initialization from this value.

  Author

  Jon S. Berndt (Engine framework code and framework-related mods)

  Dave Luff (engine operational code)

  David Megginson (initial porting and additional code)

  Ron Jensen (additional engine code)

  See also

  Taylor, Charles Fayette, "The Internal Combustion Engine in Theory and Practice"

Definition at line 223 of file FGPiston.h.

#include <FGPiston.h>

Inheritance diagram for FGPiston:

Collaboration diagram for FGPiston:

Public Member Functions
	FGPiston (FGFDMExec *exec, Element *el, int engine_number, struct Inputs &input)
	Constructor.
	~FGPiston ()
	Destructor.
double	CalcFuelNeed (void)
	The fuel need is calculated based on power levels and flow rate for that power level. More...
void	Calculate (void)
	Calculates the thrust of the engine, and other engine functions.
double	getAFR (void) const
double	getCylinderHeadTemp_degF (void) const
double	GetEGT (void) const
std::string	GetEngineLabels (const std::string &delimiter)
std::string	GetEngineValues (const std::string &delimiter)
double	getExhaustGasTemp_degF (void) const
int	GetMagnetos (void) const
double	getManifoldPressure_inHg (void) const
double	getOilPressure_psi (void) const
double	getOilTemp_degF (void) const
double	GetPowerAvailable (void) const
double	getRPM (void) const
void	ResetToIC (void)
	Resets the Engine parameters to the initial conditions.
void	SetMagnetos (int magnetos)
Public Member Functions inherited from FGEngine
	FGEngine (int engine_number, struct Inputs &input)
virtual double	CalcOxidizerNeed (void)
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
void	LoadThruster (FGFDMExec *exec, Element *el)
void	LoadThrusterInputs ()
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...
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	PutMessage (const Message &msg)
	Places a Message structure on the Message queue. More...
void	PutMessage (const std::string &text)
	Creates a message with the given text and places it on the queue. More...
void	PutMessage (const std::string &text, bool bVal)
	Creates a message with the given text and boolean value and places it on the queue. More...
void	PutMessage (const std::string &text, int iVal)
	Creates a message with the given text and integer value and places it on the queue. More...
void	PutMessage (const std::string &text, double dVal)
	Creates a message with the given text and double value and places it on the queue. More...
int	SomeMessages (void) const
	Reads the message on the queue (but does not delete it). More...
void	ProcessMessage (void)
	Reads the message on the queue and removes it from the queue. More...
Message *	ProcessNextMessage (void)
	Reads the next message on the queue and removes it from the queue. More...
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 double	PitotTotalPressure (double mach, double p)
	Compute the total pressure in front of the Pitot tube. More...
static double	MachFromImpactPressure (double qc, double p)
	Compute the Mach number from the differential pressure (qc) and the static pressure. More...
static double	VcalibratedFromMach (double mach, double p)
	Calculate the calibrated airspeed from the Mach number. More...
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). 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)
static double	GaussianRandomNumber (void)
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< FGFunction * >	PostFunctions
std::vector< FGFunction * >	PreFunctions
Static Protected Attributes inherited from FGJSBBase
static Message	localMsg
static std::queue< Message >	Messages
static unsigned int	messageId = 0
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	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/(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__
static int	gaussian_random_number_phase = 0

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 531 of file FGPiston.cpp.

{
  FuelExpended = FuelFlowRate * in.TotalDeltaT;
  if (!Starved) FuelUsedLbs += FuelExpended;
  return FuelExpended;
}

---

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

• FGPiston.h
• FGPiston.cpp