"xerj" wrote in message
...
P.S. I have a Master's in Aerospace and have worked in the industry for
many years. I will admit most of my schooling and experience was with
jets and rockets -- not pistons and props. But I do recall the equations
and techniques to calculate engine horsepower required for various flight
modes of a prop plane was VERY complex.

Yeah, those damn eggbeaters hanging out the front make it all pretty
complicated. I most certainly DON'T have a Master's in Aerospace. I find
it slightly comforting that a guy that does says it's complex.


Jets and rockets are actually much easier to do design work on than prop
planes. The jet produces thrust, which is the thrust used to propel the
plane. Calculate the thrust required then it is a simple step to calculate
fuel flow from the engine to get the thrust. With a prop, exactly what
happens as you convert rotation power into thrust is complex, complex,
complex.

Thanks for taking the time to answer.

I am CERTAIN equating thrust horsepower (thrust times velocity) to brake
horse power (torque time RPM) is wrong. Anyone have an aircraft
performance chart to look at the IAS for 75% power at sea level and at
altitude?? I am not going to say it will be exact, but I think it will be
close.

Do you mean working back from TAS to get an IAS?

I looked up a Navajo information manual. There's a chart True Airspeed vs
Density Altitude. I chose the line for 260 BHP which is around 75% of the
350 BHP engines.

At sea level the TAS is shown as around 207 MPH (have to interpolate, it's
a grid that goes up in 10s). That is obviously the IAS as well.

At 20,000, the TAS is close to 250 MPH. The inferred IAS is 184.

Any thoughts?


See my other posts. I stand corrected. For a given engine power, IASI
drops off with altitude. For a jet, IASI does not drop off for a given
engine thrust as the plane climbs. Maybe that is an inherent reason jets
are faster at altitude than a prop.

Danny Deger