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rocket engine and piston engine fixes

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This commit is contained in:
ehofman 2009-11-02 12:22:45 +00:00 committed by Tim Moore
parent a70431c5a4
commit b1eebb21a6
3 changed files with 35 additions and 16 deletions
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41
src/FDM/JSBSim/models/propulsion/FGPiston.cpp
View file

@ -88,7 +88,7 @@ FGPiston::FGPiston(FGFDMExec* exec, Element* el, int engine_number)
MinManifoldPressure_inHg = 6.5;
MaxManifoldPressure_inHg = 28.5;
ISFC = -1;
volumetric_efficiency = -0.1;
volumetric_efficiency = 0.85;
Bore = 5.125;
Stroke = 4.375;
Cylinders = 4;
@ -239,32 +239,41 @@ FGPiston::FGPiston(FGFDMExec* exec, Element* el, int engine_number)
StarterHP = sqrt(MaxHP) * 0.4;
displacement_SI = Displacement * in3tom3;
RatedMeanPistonSpeed_fps = ( MaxRPM * Stroke) / (360); // AKA 2 * (RPM/60) * ( Stroke / 12) or 2NS
// Create IFSC and VE to match the engine if not provided
int calculated_ve=0;
if (volumetric_efficiency < 0) {
volumetric_efficiency = MaxManifoldPressure_inHg / 29.92;
calculated_ve=1;
}
// Create IFSC to match the engine if not provided
if (ISFC < 0) {
double pmep = MaxManifoldPressure_inHg > 29.92 ? 0 : 29.92 - MaxManifoldPressure_inHg;
double pmep = 29.92 - MaxManifoldPressure_inHg;
pmep *= inhgtopa;
double fmep = (18400 * (2*(Stroke/12)*(MaxRPM/60)) * fttom + 46500)/2;
double fmep = (18400 * RatedMeanPistonSpeed_fps * fttom + 46500);
double hp_loss = ((pmep + fmep) * displacement_SI * MaxRPM)/(Cycles*22371);
ISFC = ( Displacement * MaxRPM * volumetric_efficiency ) / (9411 * (MaxHP+hp_loss));
ISFC = ( 1.1*Displacement * MaxRPM * volumetric_efficiency *(MaxManifoldPressure_inHg / 29.92) ) / (9411 * (MaxHP+hp_loss));
// cout <<"FMEP: "<< fmep <<" PMEP: "<< pmep << " hp_loss: " <<hp_loss <<endl;
}
if ( MaxManifoldPressure_inHg > 29.9 ) { // Don't allow boosting with a bogus number
MaxManifoldPressure_inHg = 29.9;
if (calculated_ve) volumetric_efficiency = 1.0;
}
minMAP = MinManifoldPressure_inHg * inhgtopa; // inHg to Pa
maxMAP = MaxManifoldPressure_inHg * inhgtopa;
// For throttle
RatedMeanPistonSpeed_fps = ( MaxRPM * Stroke) / (360); // AKA 2 * (RPM/60) * ( Stroke / 12) or 2NS
if(Z_airbox < 998){
double Ze=RatedMeanPistonSpeed_fps/PeakMeanPistonSpeed_fps; // engine impedence
/*
* Pm = ( Ze / ( Ze + Zi + Zt ) ) * Pa
* Where:
* Pm = Manifold Pressure
* Pa = Ambient Pressre
* Ze = engine impedance, Ze is effectively 1 / Mean Piston Speed
* Zi = airbox impedance
* Zt = throttle impedance
*
* For the calculation below throttle is fully open or Zt = 0
*
*
*
*/
if(Z_airbox < 0.0){
double Ze=PeakMeanPistonSpeed_fps/RatedMeanPistonSpeed_fps; // engine impedence
Z_airbox = (standard_pressure *Ze / maxMAP) - Ze; // impedence of airbox
}
Z_throttle=(((MaxRPM * Stroke) / 360)/((IdleRPM * Stroke) / 360))*(standard_pressure/minMAP - 1) - Z_airbox; // Constant for Throttle impedence
@ -913,7 +922,9 @@ void FGPiston::Debug(int from)
cout << " MaxThrottle: " << MaxThrottle << endl;
cout << " MinThrottle: " << MinThrottle << endl;
cout << " ISFC: " << ISFC << endl;
cout << " Volumentric Efficiency: " << volumetric_efficiency << endl;
cout << " Volumetric Efficiency: " << volumetric_efficiency << endl;
cout << " PeakMeanPistonSpeed_fps: " << PeakMeanPistonSpeed_fps << endl;
cout << " Intake Impedance Factor: " << Z_airbox << endl;
cout << endl;
cout << " Combustion Efficiency table:" << endl;

9
src/FDM/JSBSim/models/propulsion/FGRocket.cpp
View file

@ -69,6 +69,7 @@ FGRocket::FGRocket(FGFDMExec* exec, Element *el, int engine_number)
FuelFlowRate = 0.0;
OxidizerFlowRate = 0.0;
SLOxiFlowMax = 0.0;
BuildupTime = 0.0;
It = 0.0;
// Defaults
@ -77,6 +78,8 @@ FGRocket::FGRocket(FGFDMExec* exec, Element *el, int engine_number)
if (el->FindElement("isp"))
Isp = el->FindElementValueAsNumber("isp");
if (el->FindElement("builduptime"))
BuildupTime = el->FindElementValueAsNumber("builduptime");
if (el->FindElement("maxthrottle"))
MaxThrottle = el->FindElementValueAsNumber("maxthrottle");
if (el->FindElement("minthrottle"))
@ -127,7 +130,6 @@ double FGRocket::Calculate(void)
if (ThrustTable != 0L) { // Thrust table given -> Solid fuel used
if ((Throttle == 1 || BurnTime > 0.0 ) && !Starved) {
BurnTime += State->Getdt();
double TotalEngineFuelBurned=0.0;
for (int i=0; i<(int)SourceTanks.size(); i++) {
FGTank* tank = Propulsion->GetTank(i);
@ -137,6 +139,11 @@ double FGRocket::Calculate(void)
}
VacThrust = ThrustTable->GetValue(TotalEngineFuelBurned);
if (BurnTime <= BuildupTime && BuildupTime > 0.0) {
VacThrust *= sin((BurnTime/BuildupTime)*M_PI/2.0);
// VacThrust *= (1-cos((BurnTime/BuildupTime)*M_PI))/2.0; // 1 - cos approach
}
BurnTime += State->Getdt(); // Increment burn time
} else {
VacThrust = 0.0;
}

1
src/FDM/JSBSim/models/propulsion/FGRocket.h
View file

@ -200,6 +200,7 @@ private:
double OxidizerFlowRate;
double PropellantFlowRate;
bool Flameout;
double BuildupTime;
FGTable* ThrustTable;
void Debug(int from);