ORIGINAL: HighPlains
Nearly any RC model engine will unload between 1 and 2 thousand rpm in the air. I've had racing engines on pylon models unload 5000 in level flight, verified with an audio tach and doppler shift. But when you put an airplane into a dive, the rpm will really climb due to potential energy turning into kinetic. Many airplanes can see an easy 25% increase in speed, and thus higher engine rpm with it.
I have flown many pylon planes that were above 175 mph in level flight, so forward velocity is a larger factor with them,
On 3.0 I meant to say that the localized speed of the air changes with the change in pressure over the surface of the prop.
Great that you fly pylon, as that represents the upper fringe of both speed and noise level produced by model airplanes and so is very much on topic with this thread.
So, what's the bottom line? At the most extreme, in an extended dive with a screaming 5-6 hp Nelson and 7 inch prop pushing a very slippery airframe, do the numbers add up to a prop tip speed in excess of 1100 ft/sec?