Well, try a takeoff in a normally aspirated light airplane at sea level sometime, note the performance, then go land at a high altitude airport like Leadville, Colorado. (9927 feet) Then try to take off again. You better have a powerful airplane, or a lightly loaded one, or you never will take off! (Or once you do, you won't be able to climb out of ground effect!)

Lots of pilots have crashed because they didn't understand density altitude and it's effect on engines, and airplanes in general. In fact, the detriment to performance is mostly due to the engine losing power with altitude. With a turbocharger you regain a good percentage of your performance at high altitudes, that is lost with normally aspirated engines.

Full scale airplanes normally cruise at 75% power. With a fixed pitch prop, this is a certain rpm, depending on the application. As you go higher and higher, you soon reach a point where full throttle only gives you 75% power. Depending on temperature, this point is usually reached around 7000 feet or so. At any atitude above that, the engine just keeps on losing power and you can't achieve 75% power, even with full throttle, mixture leaned, etc.

A drop of a couple of hundred rpms with a model engine swinging a 16 to 24" prop over 6000 rpms is a good bit of power lost.

AV8TOR