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Propellor RPM doesn't reduce in the cruise

S

SADT

Charter Member
Some aircraft in my FSx installation have a peculiar problem: When in the cruise, and generally above the critical altitude, full throttle height for turbocharged engines, I am unable to reduce the prop RPM down to anything like cruising RPM's. For example, an Me-109K is supposed to cruise at 1.0Ata (Roughly 30in HG) and 2100 RPM. From above 22,000 feet, to 25,000 feet, 1.0 Ata (Reducing from that above those altitudes) can only be had with full throttle. When I go to reduce my RPM's down to the cruise level of 2100 RPM, (Having disconnected all hardware so there could be no interference), using Cntrl F2, I find that I can only reduce the RPM's down to roughly 2500 - from 2700 in the climb. And I don't think it's because I'm going too fast, because in this case it normally occurs as I level out of the climb, and so my airspeed only rises slowly above the climb speed - it can't generally gain speed quickly because I can't lower my RPM to cruising levels..! What generally happens is that you pull the prop lever back to about 70%, which makes the change to 2500RPM, but then you can't reduce it any more, no matter how much you move the prop lever. This is a problem I have with several aircraft in FSx..

Is there some figure I can play around in the aircraft.cfg file that changes the behavior of the propeller RPM in the cruise - ie, allowing it achieve lower RPMs? Or does this require air file editing?

Later addition: Though this aircraft has nothing to do the one above, this is the same issue I'm experiencing, put more succinctly: http://forum.avsim.net/topic/350788-rpm-limit/

Regards,
Craig.
 
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I don't have a specific answer to your question, but I do know that the MicroSoft Flight Sim engine does not properly model supercharging or turbocharging. It could be that the airfile for your Bf-109K was written so that you can achieve accurate speeds at altitude, but the trade off can be incorrect engine RPM at altitude.
 
Most of the prop effects are contained in the prop tables in the .air file. However the prop governing range and pitch limits are contained in the .cfg file.

The AFSD utility by Herve Sors allows one to monitor what is going on with the prop. An inability to further reduce RPM might be due to reaching a pitch limit. An example of this is RPM actually increasing in a high speed dive beyond normal limits.

T
 
It might be as simple as the wrong reduction gear ratio.....the prop tips maybe supersonic, hence loss of efficiency?
Keith
 
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