Bell Helo

My best guess - it could be a test flight where they are testing stability in sideward flight. The truck could be there to track speed, since the pitot tube only works when the helo is going forward.

In the helicopters I've flown there was always a limit for max speed in sideward and rearward flight so they must have got those figures from somewhere.

Of course I always wondered how I would know if I was busting the CH-47's 45 knot sideward flight limit since the airspeed would read zero.
GKY is home to the Bell SkunkWorkx. They do this type of flying all the time. Guy told me they are usually testing new rotor blades.
I shot this today at KGKY, what in the world is this helo doing? There is a pace truck under it....are they calibrating IAS?

My friend had to do this when getting his nose STC for the MD500E. Sideward flight was one of the testing parameters that the FAA test pilot completed during their test flights. They used a car to establish the necessary speed for that particular test.