Date started: 09/12/2000
Purpose: This module models a rocket engine
- ------------- Copyright (C) 2000 Jon S. Berndt (jsb@hal-pc.org) --------------
+ ------------- Copyright (C) 2000 Jon S. Berndt (jon@jsbsim.org) --------------
This program is free software; you can redistribute it and/or modify it under
- the terms of the GNU General Public License as published by the Free Software
+ the terms of the GNU Lesser General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any later
version.
This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
- FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+ FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
details.
- You should have received a copy of the GNU General Public License along with
+ You should have received a copy of the GNU Lesser General Public License along with
this program; if not, write to the Free Software Foundation, Inc., 59 Temple
Place - Suite 330, Boston, MA 02111-1307, USA.
- Further information about the GNU General Public License can also be found on
+ Further information about the GNU Lesser General Public License can also be found on
the world wide web at http://www.gnu.org.
FUNCTIONAL DESCRIPTION
INCLUDES
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/
+#include <iostream>
#include <sstream>
-
#include "FGRocket.h"
+#include "FGState.h"
+#include "models/FGPropulsion.h"
+#include "FGThruster.h"
+#include "FGTank.h"
+
+using namespace std;
namespace JSBSim {
FGRocket::FGRocket(FGFDMExec* exec, Element *el, int engine_number)
: FGEngine(exec, el, engine_number)
{
- if (el->FindElement("shr"))
- SHR = el->FindElementValueAsNumber("shr");
- if (el->FindElement("max_pc"))
- maxPC = el->FindElementValueAsNumberConvertTo("max_pc", "PSF");
- if (el->FindElement("prop_eff"))
- propEff = el->FindElementValueAsNumber("prop_eff");
+ Element* thrust_table_element = 0;
+ ThrustTable = 0L;
+ BurnTime = 0.0;
+ previousFuelNeedPerTank = 0.0;
+ previousOxiNeedPerTank = 0.0;
+ PropellantFlowRate = 0.0;
+ FuelFlowRate = 0.0;
+ OxidizerFlowRate = 0.0;
+ SLOxiFlowMax = 0.0;
+ BuildupTime = 0.0;
+ It = 0.0;
+ ThrustVariation = 0.0;
+ TotalIspVariation = 0.0;
+
+ // Defaults
+ MinThrottle = 0.0;
+ MaxThrottle = 1.0;
+
+ 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"))
SLFuelFlowMax = el->FindElementValueAsNumberConvertTo("slfuelflowmax", "LBS/SEC");
if (el->FindElement("sloxiflowmax"))
SLOxiFlowMax = el->FindElementValueAsNumberConvertTo("sloxiflowmax", "LBS/SEC");
- if (el->FindElement("variance"))
- Variance = el->FindElementValueAsNumber("variance");
+
+ // 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");
+ }
+ }
+ }
+
+ bindmodel();
Debug(0);
Type = etRocket;
Flameout = false;
- PC = 0.0;
- kFactor = (2.0*SHR*SHR/(SHR-1.0))*pow(2.0/(SHR+1), (SHR+1)/(SHR-1));
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
FGRocket::~FGRocket(void)
{
+ delete ThrustTable;
Debug(1);
}
double FGRocket::Calculate(void)
{
- double Cf=0;
+ double dT = State->Getdt()*Propulsion->GetRate();
+ double thrust;
if (!Flameout && !Starved) ConsumeFuel();
+ PropellantFlowRate = (FuelExpended + OxidizerExpended)/dT;
Throttle = FCS->GetThrottlePos(EngineNumber);
- if (Throttle < MinThrottle || Starved) {
- PctPower = Thrust = 0.0; // desired thrust
- Flameout = true;
- PC = 0.0;
+ // If there is a thrust table, it is a function of propellant burned. The
+ // engine is started when the throttle is advanced to 1.0. After that, it
+ // burns without regard to throttle setting.
+
+ if (ThrustTable != 0L) { // Thrust table given -> Solid fuel used
+
+ if ((Throttle == 1 || BurnTime > 0.0 ) && !Starved) {
+ double TotalEngineFuelBurned=0.0;
+ for (int i=0; i<(int)SourceTanks.size(); i++) {
+ FGTank* tank = Propulsion->GetTank(i);
+ if (SourceTanks[i] == 1) {
+ TotalEngineFuelBurned += tank->GetCapacity() - tank->GetContents();
+ }
+ }
+
+ VacThrust = ThrustTable->GetValue(TotalEngineFuelBurned)
+ * (ThrustVariation + 1)
+ * (TotalIspVariation + 1);
+ 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;
+ }
+
+ } else { // liquid fueled rocket assumed
+
+ if (Throttle < MinThrottle || Starved) { // Combustion not supported
+
+ PctPower = 0.0; // desired thrust
+ Flameout = true;
+ VacThrust = 0.0;
+
+ } else { // Calculate thrust
+
+ // This is nonsensical. Max throttle should be assumed to be 1.0. One might
+ // conceivably have a throttle setting > 1.0 for some rocket engines. But, 1.0
+ // should always be the default.
+ // PctPower = Throttle / MaxThrottle; // Min and MaxThrottle range from 0.0 to 1.0, normally.
+
+ PctPower = Throttle;
+ Flameout = false;
+ VacThrust = Isp * PropellantFlowRate;
+
+ }
+
+ } // End thrust calculations
+
+ thrust = Thruster->Calculate(VacThrust);
+ It += thrust * dT;
+
+ return thrust;
+}
+
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+// This overrides the base class ConsumeFuel() function, for special rocket
+// engine processing.
+
+void FGRocket::ConsumeFuel(void)
+{
+ unsigned int i;
+ FGTank* Tank;
+ bool haveOxTanks = false;
+ double Fshortage=0, Oshortage=0, TanksWithFuel=0, TanksWithOxidizer=0;
+
+ if (FuelFreeze) return;
+ if (TrimMode) return;
+
+ // Count how many assigned tanks have fuel for this engine at this time.
+ // If there is/are fuel tanks but no oxidizer tanks, this indicates
+ // a solid rocket is being modeled.
+
+ for (i=0; i<SourceTanks.size(); i++) {
+ Tank = Propulsion->GetTank(SourceTanks[i]);
+ switch(Tank->GetType()) {
+ case FGTank::ttFUEL:
+ if (Tank->GetContents() > 0.0 && Tank->GetSelected()) ++TanksWithFuel;
+ break;
+ case FGTank::ttOXIDIZER:
+ haveOxTanks = true;
+ if (Tank->GetContents() > 0.0 && Tank->GetSelected()) ++TanksWithOxidizer;
+ break;
+ }
+ }
+
+ // If this engine has burned out, it is starved.
+
+ if (TanksWithFuel==0 || (haveOxTanks && TanksWithOxidizer==0)) {
+ Starved = true;
+ return;
+ }
+
+ // Expend fuel from the engine's tanks if the tank is selected as a source
+ // for this engine.
+
+ double fuelNeedPerTank = CalcFuelNeed()/TanksWithFuel;
+ double oxiNeedPerTank = CalcOxidizerNeed()/TanksWithOxidizer;
+
+ for (i=0; i<SourceTanks.size(); i++) {
+ Tank = Propulsion->GetTank(SourceTanks[i]);
+ if ( ! Tank->GetSelected()) continue; // If this tank is not selected as a source, skip it.
+ switch(Tank->GetType()) {
+ case FGTank::ttFUEL:
+ Fshortage += Tank->Drain(2.0*fuelNeedPerTank - previousFuelNeedPerTank);
+ previousFuelNeedPerTank = fuelNeedPerTank;
+ break;
+ case FGTank::ttOXIDIZER:
+ Oshortage += Tank->Drain(2.0*oxiNeedPerTank - previousOxiNeedPerTank);
+ previousOxiNeedPerTank = oxiNeedPerTank;
+ break;
+ }
+ }
+
+ if (Fshortage < 0.00 || (haveOxTanks && Oshortage < 0.00)) Starved = true;
+ else Starved = false;
+}
+
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+//
+// The FuelFlowRate can be affected by the TotalIspVariation value (settable
+// in a config file or via properties). The TotalIspVariation parameter affects
+// thrust, but the thrust determines fuel flow rate, so it must be adjusted
+// for Total Isp Variation.
+
+double FGRocket::CalcFuelNeed(void)
+{
+ double dT = State->Getdt()*Propulsion->GetRate();
+
+ 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 {
- PctPower = Throttle / MaxThrottle;
- //todo: remove Variance?
- PC = maxPC*PctPower * (1.0 + Variance * ((double)rand()/(double)RAND_MAX - 0.5));
- // The Cf (below) is CF from Eqn. 3-30, "Rocket Propulsion Elements", Fifth Edition,
- // George P. Sutton. Note that the thruster function GetPowerRequired() might
- // be better called GetResistance() or something; this function returns the
- // nozzle exit pressure.
- Cf = sqrt(kFactor*(1 - pow(Thruster->GetPowerRequired()/(PC), (SHR-1)/SHR)));
- Flameout = false;
+ FuelFlowRate = SLFuelFlowMax*PctPower;
}
- return Thruster->Calculate(Cf*maxPC*PctPower*propEff);
+ FuelExpended = FuelFlowRate*dT; // For this time step ...
+ return FuelExpended;
+}
+
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+double FGRocket::CalcOxidizerNeed(void)
+{
+ double dT = State->Getdt()*Propulsion->GetRate();
+ OxidizerFlowRate = SLOxiFlowMax*PctPower;
+ OxidizerExpended = OxidizerFlowRate*dT;
+ return OxidizerExpended;
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-string FGRocket::GetEngineLabels(string delimeter)
+string FGRocket::GetEngineLabels(const string& delimiter)
{
std::ostringstream buf;
- buf << Name << "_ChamberPress[" << EngineNumber << "]" << delimeter
- << Thruster->GetThrusterLabels(EngineNumber, delimeter);
+ buf << Name << " Total Impulse (engine " << EngineNumber << " in psf)" << delimiter
+ << Thruster->GetThrusterLabels(EngineNumber, delimiter);
return buf.str();
}
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-string FGRocket::GetEngineValues(string delimeter)
+string FGRocket::GetEngineValues(const string& delimiter)
{
std::ostringstream buf;
- buf << PC << delimeter << Thruster->GetThrusterValues(EngineNumber, delimeter);
+ buf << It << delimiter << Thruster->GetThrusterValues(EngineNumber, delimiter);
return buf.str();
}
+//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+// This function should tie properties to rocket engine specific properties
+// that are not bound in the base class (FGEngine) code.
+//
+void FGRocket::bindmodel()
+{
+ string property_name, base_property_name;
+ base_property_name = CreateIndexedPropertyName("propulsion/engine", EngineNumber);
+
+ property_name = base_property_name + "/total-impulse";
+ PropertyManager->Tie( property_name.c_str(), this, &FGRocket::GetTotalImpulse);
+ property_name = base_property_name + "/vacuum-thrust_lbs";
+ PropertyManager->Tie( property_name.c_str(), this, &FGRocket::GetVacThrust);
+
+ if (ThrustTable) { // Solid rocket motor
+ property_name = base_property_name + "/thrust-variation_pct";
+ PropertyManager->Tie( property_name.c_str(), this, &FGRocket::GetThrustVariation,
+ &FGRocket::SetThrustVariation);
+ property_name = base_property_name + "/total-isp-variation_pct";
+ PropertyManager->Tie( property_name.c_str(), this, &FGRocket::GetTotalIspVariation,
+ &FGRocket::SetTotalIspVariation);
+ } else { // Liquid rocket motor
+ property_name = base_property_name + "/oxi-flow-rate-pps";
+ PropertyManager->Tie( property_name.c_str(), this, &FGRocket::GetOxiFlowRate);
+ }
+}
+
//%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
// The bitmasked value choices are as follows:
// unset: In this case (the default) JSBSim would only print
if (debug_lvl & 1) { // Standard console startup message output
if (from == 0) { // Constructor
cout << " Engine Name: " << Name << endl;
- cout << " Specific Heat Ratio = " << SHR << endl;
- cout << " Maximum Chamber Pressure = " << maxPC << endl;
- cout << " Propulsive Efficiency = " << propEff << endl;
- cout << " MaxThrottle = " << MaxThrottle << endl;
- cout << " MinThrottle = " << MinThrottle << endl;
- cout << " FuelFlowMax = " << SLFuelFlowMax << endl;
- cout << " OxiFlowMax = " << SLOxiFlowMax << endl;
- cout << " Variance = " << Variance << endl;
+ cout << " Vacuum Isp = " << Isp << endl;
+ cout << " Maximum Throttle = " << MaxThrottle << endl;
+ cout << " Minimum Throttle = " << MinThrottle << endl;
+ cout << " Fuel Flow (max) = " << SLFuelFlowMax << endl;
+ cout << " Oxidizer Flow (max) = " << SLOxiFlowMax << endl;
+ cout << " Mixture ratio = " << SLOxiFlowMax/SLFuelFlowMax << endl;
}
}
if (debug_lvl & 2 ) { // Instantiation/Destruction notification
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