These are engine stands that I have designed and built for multiple UAV engine's for Eastcor Engineering (http://www.eastcoreng.com/). The stands have no metal in them for testing purposes and had to be strong enough to run the engines with the propellers on them at full speed. I used the these stands to test and check for any kind of underlying RF signature that the engines would give off. The idea was that each engine, even of the same model would give off a unique harmonic frequency much like an aircraft carrier or destroyer naval ship. We found that engines all gave off what seemed a unique signature but overall was a fail. The signal wasn't strong enough to be captured over longer distances (flight distance).