[quote]ORIGINAL: FHHuber

Denser air means you need LESS power to stay airborne at the same weight.

Hot air is less dense than cold air.

Moisture adds some density.

elevation above sea level has a large effect on density (higher above sea level... less dense.)


Dear FH....
One of the above statements is not correct. (Sorry to sound so "authorative"). Air with moisture content actually is less dense than dry air.

The average molecular weight of air is about 29 units. The molecular weight of water vapor is 18. Thus if any of the air is displaced with water vapor, the average density of the combination will be less than dry air. Many folks will say the air feels "heavy" on a humid day. Actually the air mass is less dense, but feels less comfortable.

I agree with everything else you have mentioned regarding engine power at various altitudes and air temperatures. Full scale pilots concern themselves with "Density Altitude", which is a number calculated from the actual height above sea level, corrected for temperature, humidity, etc. It is not uncommon for density altitude at sea level to be over several thousand feet on a hot day.

Bill