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I am very curious as to which "industry" was the source of this alleged "standard" :
"....industry standard (verifable in any STC POH) is: (RPM/2700)*(MAP/29)=HP..."
The SAE standard equation for HP is:
HP (measured) = Torque x RPM / 5252.
That standard has been adopted by practically every industry I can think of. The "standard" HP which manufacturers advertise is generally accepted as the power produced at atmospheric conditions of 29.92 in. hg. barometric pressure, 59°F atmospheric pressure, and a specified relative humidity.
There are other "standard" atmospheric conditions used by some car manufacturers (and by Lycoming) to achieve higher advertised power levels. There is also an accepted methodology for correcting a measurement taken at some other set of atmospheric conditions back to the standard.
The alleged "industry standard" equation (quoted above) looks as if it might be an attempt to calculate a power output at known conditions based on the known (actually, advertised) max engine power.
If that is the case, then the equation should look like this:
calculated-HP = rated HP * (actual-RPM / Rating-RPM) * (actual-MAP / rating-MAP)
The quoted "2700" figure only applies to engines rated at 2700. If you had a Lyc rated at 290 HP at 2575 RPM on 29.5" MAP, operating at 2300 RPM on 25" MAP, then the APPROXIMATE power (from that equation) would be 219 HP.
BTW, that equation produces only an APPROXIMATION, because it is well-known that power is not linear with MAP, but for normally aspirated engines, it approximates linear between about 20" and 29" MAP, and can vary significantly with the reduced backpressure experienced at altitude.
If you doubt that, just examine the equations and curves which Lycoming publishes to determine HP from known operating conditions.
Hope that helps.
Jack Kane
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