In YASim, propellers start turning backwards instead of windmilling.
This code in PropEngine.cpp might be the problem:
// Euler-integrate the RPM. This doesn't need the full-on
// Runge-Kutta stuff.
float rotacc = (engTorque-propTorque)/Math::abs(_moment);
_omega += dt * rotacc;
If then engine is idling (or close to it), it never manages to produce
produce the torque required by the propeller, so rotacc is negative;
very quickly, _omega (the revolution velocity) ends up negative as
well.
In real life, the propeller will keep spinning in a positive direction
(a bit below the current airspeed divided by its advance ratio, I
think), and will instead impose a negative thrust on the airplane --
the plane is pushing the propeller, rather than the propeller pulling
the plane. In a 100 kt gliding descent, the propeller may well be
spinning at 2000 rpm, but it's also adding drag (or negative thrust)
to get there.
This is a very important effect for approach: pulling the power below
a certain point (often about 1500 rpm at approach speed) in a typical
fixed-pitch C172 or Cherokee will have a significant effect on how
fast the plane comes down. It also matters for modelling an
engine-out in a twin.
All the best,
David
--
David Megginson, [EMAIL PROTECTED], http://www.megginson.com/
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