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Gary,
OK.
But - in your second formulation, the max calculated power is
only 80% when I know that, with everything fire walled at sea level and dry cold
air, it is 100% - unless I am flying at 200 KIAS, then the new 100% is
probably 105% times the old. :-) Thank heavens the SAE has a different standard
for calculating HP.
Perhaps an Excel app on your I-phone would help you in the air.
Grayhawk
In a message dated 5/20/2009 1:59:20 P.M. Central Daylight Time,
casey.gary@yahoo.com writes:
Grayhawk,
Too late {:-) I already looked at it. I compared it to the rough
formula I have always used - % power = RPM/RPMmax * MAP/MAPmax - and it
comes within 1% of it. I stopped there and didn't try to "reverse
engineer" the formula, except I have hunch it has to do with assuming the max
RPM is 2500 (the 2.5) and the max MAP is 35 inches (the 3.5).
Regardless, the formulas are not quite right. As rpm increases,
engine friction increases and volumetric efficiency decreases so the increase
in power won't go up directly with RPM. The opposite is true of MAP.
It takes a certain MAP just to power the engine (overcome friction) so
power will increase more than the increase in MAP. How much are these
effects? Without real data it would be hard to say, but in the RPM and
MAP ranges that are useful in aircraft engines the factor for rpm might be
something like 0.8. For MAP there is a subtractive term of about 10 inches.
The equation would then look like %power = (RPM/RPMmax*0.8) *
(MAP-10)/MAPmax-10). Gets hard to do in your head (well, mine anyway),
so I just remember that a 10% reduction in RPM will drop the power less than
10%, but a 10% drop in MAP will drop the power by more than 10%. Then
there is the effect of altitude..
Gary
From: Lancair Mailing List
<lml@lancaironline.net>
Se
Ignore the formula. I got it from a very old email and it is
wrong. Perhaps Walter will correct it.
Grayhawk the brainless
In a message dated 5/18/2009 7:39:13 P.M. Central Daylight Time,
Sky2high@aol.com writes:
Finally, thanks to Walter at GAMI,
%HP = 100-((max RPM/100-RPM)*2.5+(Max MP-MP)*3.5)
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