Fuel Burn - I think someone mentioned this once
Yes, this is definitely messed up (for JSBSim at least. I have not investigated any of the others). Some issues I've found are: the density of the fuel is wrong, somewhere along the line gallons are passed to a method which expects pounds, and the specific fuel consumption resulting from the power calulation is a little bit off. I added an adjustable parameter in the JSBSim engine file for that. Let me see if I can find some code to paste here (a diff will be rather meaningless by now)...
// From src/FDM/JSBSim/FGPiston.cpp:
// in FGPistion()
// init default fuel-flow adjustment
ff_adjustment(0.92), // get an (optional) adjustment value from the config
else if (token == "FF_SCALAR") *Eng_cfg >> ff_adjustment; // in doAirFlow()
// the '2' below is supposed to be 'Cycles'
// double swept_volume = (displacement_SI * (RPM/60)) / 2;
double swept_volume = (displacement_SI * (RPM/60)) / Cycles; // in doFuelFlow()
// see ff_adjustment declaration above.
m_dot_fuel = m_dot_air / sr_fuel * equivalence_ratio *ff_adjustment;
// keeping gph, but FGTank knows about fuel in pounds, not gals
// so adding _pph for ConsumeFuel()
FuelFlow_pph = m_dot_fuel
* 3600 // seconds to hours
* 2.2046; // kg to lb
// changed 'kerosine' to 'av-gas' (6.6 to 6.0)
// eventually we'll want to config this so that we
// can burn deisel, alcohol or hydrogen (for example).
FuelFlow_gph = FuelFlow_pph / 6.0; // lb to gal_us of av-gas // in CalcFuelNeed()
// FGTank knows about pounds, not gallons
return FuelFlow_pph / 3600 * State->Getdt() * Propulsion->GetRate();Kris
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