I want to know what the true effect of altitude has on usable power for out model planes. Anyone have a hand on this? I know there are other factors that will make the air more or less conducive to producing power, but for now lets compare the same air at different altitudes.

I know with CI engines that less air density means less power. I also know that the prop would have less grab on the air. I have herd that this goes a long way in evening out RPM readings for CI engines, but of course the thrust will be less in thinner air.

I don't know what I am doing here, but this is what I tried. I ran a search for Density altitude calculator & found http://www.pilotfriend.com/calculato...itude_calc.htm and came up with this.

If at sea level the Air Density is 29.92 that same air would be 25.36Hg @4500 feet.

I then plugged these numbers into my trusty thrust calculator and came out with this.

If the thrust is 16pounds @ sea level it will be 13.6 pounds at 4500 feet.
If thrust is 16 pounds @ 4500 feet it will be 19 pounds at sea level.

Now, I don't know if any of this would stand up to empirical tests. I sure would be fun to find out.