On Fri, 2008-12-19 at 23:28 -0700, John Denker wrote: > Consider the following scenario: The Sim World c182rg is sitting on > the runway at KSFO. The propeller control is pulled back, so that the > engine is operating at relatively low revs, about 1750 RPM in > contrast to redline which is 2400 RPM. The pilot can observe that if > the throttle is open anywhere between 52% and 100% open, moving the > throttle has no effect on the MAP. Similarly, it has no effect on the > shaft power of the engine, as you can confirm by looking at the > property tree. This insensitivity to throttle setting is dramatically > unlike what is seen in a Real World Cessna 182RG. > > This buggy behavior is a direct consequence of the FGPiston.cpp code: > suction_loss = RPM > 0.0 ? ThrottlePos * MaxRPM / RPM : 1.0; > if (suction_loss > 1.0) suction_loss = 1.0; > MAP = p_amb * suction_loss;
John, You've just convinced me you don't have a clue what is happening inside this code. Maybe I should have documented it better, but... Let me explain what I see happening here: The propeller configuration is loading the engine configuration down. This could be because the c_power for the prop configuration is too high, or it could be because the prop pitch is set to go too high, or it could be because engine is underpowered. It is definitely not because code section you seem to love going on about. Run the math: 1 * 2500 / 1750 = 1.45, which is clipped to 1. Suction_loss is a multiplier. A multiplier of 1 has no effect. That makes manifold pressure equal ambient pressure. This section of code has the engine set to the highest power it can put out. Which isn't enough to speed the propeller up. If that is wrong, it is configuration not code. Ron ------------------------------------------------------------------------------ _______________________________________________ Flightgear-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/flightgear-devel
