RE: Boomerang Sprint Build Thread!
Why don't you use a GPS device, like Eagle Tree? It does not require any External apparatus.
A number of our club members bought a Wrist based Garmin GPS (Fortrex 101), for $40, from Aldi's of all places. We took off the Wrist Band and Velcro it in to the aircraft. In the aircraft, it is only useful for Max Speed and Total Distance Traveled, but it was cheap and you can stick it in any airplane. It is quite accurate.