ORIGINAL: highhorse
Dr Honda: I hope you are wrong. Otherwise, how can the folks at RCJI publish comparisons? Surely the weather changes would invalidate their data...
Tim: Thanks, but I'm NOT looking for definitions of air density, please re-read the OP ;-)
I'm looking for quantitative correlations between density and thrust for a given engine.
Well... I'm sure someone could come up with a VERY general formula. But at minimum... it would have to be adjusted for each class of engine. Also... it wouldn't be very accurate.
One thing to think about... when flying full scale, we can calculate performance based on Temp, and altitude. But all that is based off of lifting of the wings, and the available thrust from the prop. (another wing) Also... when working with a piston engine, we can make some assumptions on "Power" based on air density since the engine has a "Positive Displacement." So... putting some inefficiencys aside... we know a 4.0L engine will displace 4.0L within its normal cycle. With our RC jets... do you have any idea of how much air it draws? (I don't) Also... since we are dealing with a centrifugal compressor We don't have a volume reference based on "Engine Cycle." So... we would have to experimentally find the volume of the engine, in reference to RPM. That also means that EVERY engine would have a different correction factor.
You have to remember... our thrust is just the "Left Overs" from the engine running. If we had a prop or fan... we would have thrust based off of pressure density. (and the engien thrust would be negligible)
With all that said... I'm new to RC Jet's... and I don't fly full scale jets, so I could be off base.