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beta_min?

PRB

PRB

Administrator
Staff member
I was having problems with the default Grumman Goose. The RPM controls would not respond at all. The RPM responded a little to manifold pressure changes, but it was as if the RPM levers were disconnected. After some troubleshooting, I found that the new OZX “High Performance” model did not have this problem. I “fixed” it by changing the beta_min value in the [propeller] section of the aircraft.cfg from 19 to 9 (this is the value in the new “HP” OZX version.). So, what did I do?

Original thread here:

http://www.sim-outhouse.com/sohforums/showthread.php?p=207968#post207968
 
Paul:

The beta is the angle of the propeller blade. 9 degrees is a much finer blade angle and loads the engine less at the same RPM. Several factors affect the pitch/thrust/RPM relationships. The min governing RPM in the CFG, the Min MP values, and the min and max beta values. To add a bit of obfuscation, this stuff is run through a propeller table in the .air file, which can also have a great effect on the thrust delivered at any given set of conditions.

The AFSD utility is usefull here as you can directly observe the relationship between the beta, RPM, eng HP and delivered thrust at any given time.

Cheers: Tom
 
First, about the OZX G21. It overwrites the stock model, so if you want access to the original, back it up first. (beta_min on the original is 15, not 19)

Next, the problem with the stock G21 is the air file, not the aircraft.cfg file. Test fly the original with a test panel and you'll see that prop beta is always 15 at sea-level, as if it was configured with a fixed-pitch prop. The reason it behaves this way is that section 512 in the air file doesn't match the power rating of the engine. Your change to beta_min = 9 allows FSX to extrapolate power coefficient values from section 512 than are actually in the air file. The real fix is to do what OZX did and replace section 512.
 
Interesting.

I did backup the original Goose, and saw that the original beta_min was 15. The problem with the “fixed pitch behavior” does still exist in the new OZX planes, but only the 450 HP air file, and not the new “high performance” 600 HP ones. In any case, setting the beta_min to 9 “fixes” it.
 
My comments were directed at the stock air file. I've looked at, but haven't really tested the OZX air files. However, the same explanation applies - both OZX air files use the same prop tables but have significantly different engine power outputs.
 
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