Re: yasim and constant speed props??

On Tuesday 21 February 2006 02:40, Dave Perry wrote:
> Some questions concerning YASIM and constant speed props (from
> flying the pa24-250):
>
> 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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