yasim and constant speed props??

Lee Elliott

2006-02-21 19:09:43 UTC

Post by Dave Perry
Some questions concerning YASIM and constant speed props (from
1. At manifold pressures below 20 in. hg, the pa24-250 has
much too much power compared to the real AC. I normally use
16 in of manifold pressure in procedure turns and then with
the gear down and 15 deg. of flaps, the descent and airspeed
fall in place at the outer marker. I can't even carry 10 in
MP in the yasim model in an approach. 2. A likely related
issues is that with the prop all the way "forward" (normal
landing procedure), the RPM stays high at 85 mph and no
throttle as I flare out. In the real AC, the engine cannot
keep the prop at high RPM in this situation. This makes
taxiing require a lot of braking or you can pull the prop
back, again not real. Also, parked, with the prop "forward"
and no throttle, the RPM builds to perhaps 1800 RPM. The
normal engine run-up is to 2000 RPM and getting it there
requires nearly 20 in. hg MP. Again not realistic. Any
suggestions form others using yasim with a constant speed
prop.
3. The cruise speeds are very nearly correct if I lean at
altitude to the proper fuel flow. If I leave the mixture
rich, the speeds at altitude are too high. The egt does not
help me peak lean as leaning does not change the egt value.
Have I tied the egt to the wrong property?
I have thought that yasim did not handle constant speed props
well before when I could not get the p51 to slow up with the
prop forward and little or no throttle. I don't know if I can
help tweak this. I have done only a little little C++
programing. Most of my programming has been numerical
analysis in Fortran and C.
Willing to try,
Dave Perry

Hello Dave,

I don't know if this helps but while messing around with the
TU-114 I found that if I omitted the control _input_ axis for
the prop pitch I could then see the prop pitch changing as
airspeed increased. Unfortunately though, the pitch seemed to
start at 0.48 and dropped to 0.0 by a couple of hundred knots
ias. This is most likely due to me mis-configuring the props as
it's not something I know much about.

If I included the control input for the prop pitch then the pitch
seemed to stay set at whatever was specified - no constant-speed
effect.

LeeE

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