After Rock mentioned airspeed pitots I got to digging around and discovered a company called Eagle Tree. They have in-flight data recording or even real-time for such data as: airspeed, engine rpm, head temp, altitude, telemetry, and even acceleration. If ever you wanted to know what that static rpm translates to in the air this is the toy! I think you could also calculate prop efficiency, airframe drag, actual wingloads, etc......... I got to have one of these!

[link]http://www.eagletreesystems.com/[/link]