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;
This effect of this code can be understood by reference to
http://www.av8n.com/fly/throttle.htm#fig-x1x-rc2
In the figure, observe that when the revs are 1 in the
local units, three of the five throttle settings have the same MAP
and the same power. That is to say, moving the throttle will move you
from one blue curve to another, but since three of the five blue
curves lie one atop the other, this has no effect. Ditto for the red
curves.
An alternative approach is diagrammed at
http://www.av8n.com/fly/throttle.htm#fig-x1xt
This is more plausible in terms of the physics of the situation, and
more consistent with everyday Real World pilot experience.
Fixing this would have immediate benefits for not just the 182 and
182rg but indeed for all the JSBSIM piston aircraft.
For details on all this, see
http://www.av8n.com/fly/throttle.htm
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