#include "PistonEngine.hpp"
namespace yasim {
-const static float HP2W = 745.7;
-const static float CIN2CM = 1.6387064e-5;
+const static float HP2W = 745.7f;
+const static float CIN2CM = 1.6387064e-5f;
+const static float RPM2RADPS = 0.1047198f;
PistonEngine::PistonEngine(float power, float speed)
{
_boost = 1;
_running = false;
- _cranking = false;
+ _fuel = true;
// Presume a BSFC (in lb/hour per HP) of 0.45. In SI that becomes
// (2.2 lb/kg, 745.7 W/hp, 3600 sec/hour) 7.62e-08 kg/Ws.
- _f0 = power * 7.62e-08;
+ _f0 = power * 7.62e-08f;
_power0 = power;
_omega0 = speed;
// Further presume that takeoff is (duh) full throttle and
// peak-power, that means that by our efficiency function, we are
// at 11/8 of "ideal" fuel flow.
- float realFlow = _f0 * (11.0/8.0);
- _mixCoeff = realFlow * 1.1 / _omega0;
+ float realFlow = _f0 * (11.0f/8.0f);
+ _mixCoeff = realFlow * 1.1f / _omega0;
_turbo = 1;
_maxMP = 1e6; // No waste gate on non-turbo engines.
float P = P0 * (1 + _boost * (_turbo - 1));
if(P > _maxMP) P = _maxMP;
float T = Atmosphere::getStdTemperature(0) * Math::pow(P/P0, 2./7.);
- _rho0 = P / (287.1 * T);
+ _rho0 = P / (287.1f * T);
}
void PistonEngine::setDisplacement(float d)
return _power0;
}
-void PistonEngine::setThrottle(float t)
-{
- _throttle = t;
-}
-
-void PistonEngine::setStarter(bool s)
-{
- _starter = s;
-}
-
-void PistonEngine::setMagnetos(int m)
-{
- _magnetos = m;
-}
-
-void PistonEngine::setMixture(float m)
-{
- _mixture = m;
-}
-
-void PistonEngine::setBoost(float boost)
-{
- _boost = boost;
-}
-
-bool PistonEngine::isRunning()
-{
- return _running;
-}
-
bool PistonEngine::isCranking()
{
- return _cranking;
+ return _starter;
}
float PistonEngine::getTorque()
void PistonEngine::calc(float pressure, float temp, float speed)
{
- if (_magnetos == 0) {
- _running = false;
- _mp = _rho0;
- _torque = 0;
- _fuelFlow = 0;
- _egt = 80; // FIXME: totally made-up
- return;
- }
-
- _running = true;
- _cranking = false;
-
- // TODO: degrade performance on single magneto
+ if(_magnetos == 0 || speed < 60*RPM2RADPS)
+ _running = false;
+ else if(_fuel == false)
+ _running = false;
+ else
+ _running = true;
// Calculate manifold pressure as ambient pressure modified for
// turbocharging and reduced by the throttle setting. According
// to Dave Luff, minimum throttle at sea level corresponds to 6"
// manifold pressure. Assume that this means that minimum MP is
- // always 20% of ambient pressure.
+ // always 20% of ambient pressure. (But that's too much idle
+ // power, so use 10% instead!) But we need to produce _zero_
+ // thrust at that setting, so hold onto the "output" value
+ // separately. Ick.
_mp = pressure * (1 + _boost*(_turbo-1)); // turbocharger
- _mp *= (0.2 + 0.8 * _throttle); // throttle
- if(_mp > _maxMP) _mp = _maxMP; // wastegate
+ float mp = _mp * (0.1f + 0.9f * _throttle); // throttle
+ _mp *= _throttle;
+ if(mp > _maxMP) mp = _maxMP; // wastegate
// Air entering the manifold does so rapidly, and thus the
// pressure change can be assumed to be adiabatic. Calculate a
// temperature change, and use that to get the density.
- float T = temp * Math::pow(_mp/pressure, 2.0/7.0);
- float rho = _mp / (287.1 * T);
+ float T = temp * Math::pow(mp/pressure, 2.0/7.0);
+ float rho = mp / (287.1f * T);
// The actual fuel flow is determined only by engine RPM and the
// mixture setting. Not all of this will burn with the same
// efficiency.
_fuelFlow = _mixture * speed * _mixCoeff;
+ if(_fuel == false) _fuelFlow = 0;
// How much fuel could be burned with ideal (i.e. uncorrected!)
// combustion.
else if(r < .625) burned = _fuelFlow;
else if(r > 1.375) burned = burnable;
else
- burned = _fuelFlow + (burnable-_fuelFlow)*(r-.625)*(4.0/3.0);
+ burned = _fuelFlow + (burnable-_fuelFlow)*(r-0.625f)*(4.0f/3.0f);
+
+ // Correct for engine control state
+ if(!_running)
+ burned = 0;
+ if(_magnetos < 3)
+ burned *= 0.9f;
// And finally the power is just the reference power scaled by the
// amount of fuel burned, and torque is that divided by RPM.
float power = _power0 * burned/_f0;
_torque = power/speed;
+ // Figure that the starter motor produces 15% of the engine's
+ // cruise torque. Assuming 60RPM starter speed vs. 1800RPM cruise
+ // speed on a 160HP engine, that comes out to about 160*.15/30 ==
+ // 0.8 HP starter motor. Which sounds about right to me. I think
+ // I've finally got this tuned. :)
+ if(_starter && !_running)
+ _torque += 0.15f * _power0/_omega0;
+
+ // Also, add a negative torque of 8% of cruise, to represent
+ // internal friction. Propeller aerodynamic friction is too low
+ // at low RPMs to provide a good deceleration. Interpolate it
+ // away as we approach cruise RPMs (full at 50%, zero at 100%),
+ // though, to prevent interaction with the power computations.
+ // Ugly.
+ if(speed > 0 && speed < _omega0) {
+ float interp = 2 - 2*speed/_omega0;
+ interp = (interp > 1) ? 1 : interp;
+ _torque -= 0.08f * (_power0/_omega0) * interp;
+ }
+
// Now EGT. This one gets a little goofy. We can calculate the
// work done by an isentropically expanding exhaust gas as the
// mass of the gas times the specific heat times the change in
// account for non-thermodynamic losses like internal friction;
// 10% should do it.
- float massFlow = _fuelFlow + (rho * 0.5 * _displacement * speed);
+ float massFlow = _fuelFlow + (rho * 0.5f * _displacement * speed);
float specHeat = 1300;
- float corr = 1.0/(Math::pow(_compression, 0.4) - 1);
- _egt = corr * (power * 1.1) / (massFlow * specHeat);
+ float corr = 1.0f/(Math::pow(_compression, 0.4f) - 1.0f);
+ _egt = corr * (power * 1.1f) / (massFlow * specHeat);
+ if(_egt < temp) _egt = temp;
}
}; // namespace yasim
projects / flightgear.git / blobdiff