Gary,

 

In reviewing the WOT performance curves for O-360-A, I note that they converge to 0 power at 59,000 ft. This would equate to around 0.24 inHg at 0 C. Seems like this would inicate the fixed parasitic loses. Certainly, the normal operating loses are substantially higher, but the majority vary with cylinder pressure and/or RPM and will increase along with these parameters anyway.

 

I doubt that this number includes the vacuum pump or alternator output to anything not directly serving the engine, so the power from these areas would still need to be added to the 0.24" value.

 

The spec for this engine is 180 hp @ 28 inHg, so the net power / pressure ratio works out to 6.486 hp / in Hg.

 

Using the current and voltage output from a given plane while in the interested flight regime one could easily determine the fixed electrical loss to add to the 0.24". The vacuum pump is only a small fraction of this loss. Say you consume 20 amps at 12 volts. That is 240 watt or about .05 in Hg. Adding a little more for the vacuum pump would bring the fixed loss to 0.3 in Hg.

 

Seems a reasonable approach. Any comments?

 

Rob