Speed and speed measurement is naturally a constant topic for pylon racers. Accurate measurement of how much motors unload in the air would also be very useful information.
A program has been found that purports to be able to determine the speed and rpm of a model aircraft in the air.
I thought I would post the link, just in case someone is adventurous and has the time to play with it.
SPEED MEASUREMENT and it came from the
Pylon Racing Down Under web site.