ORIGINAL: av8tor1977

Well then why, when I jump into a Cessna 172 for example, which has a fixed pitch prop and a carb with mixture adjustable, is it that at sea level full throttle will produce 2700 rpms, but when I arrive at say 8000 feet, full throttle only produces about 2400 rpms??

And we can take airspeed out of the equation. Because the same basic reduction in rpm is apparent on the ground in a static runup.

Another example, but with two strokes. To maintain the same full throttle rpms in my ultralight with a Rotax 503 at 7000 feet base altitude as I was getting at a sea level airport, I had to reduce the pitch of the prop by several degrees? (And this is with proper re-jetting for the altitude change applied.)

I am a flight instructor with a couple thousand hours logged. I have never seen an engine that didn't lose rpms with altitude, unless it was turbo charged, and even then it will lose power and rpms above a certain altitude where the tubo can no longer supply sea level manifold pressure or more.....

AV8TOR