Can you fly a plane in a wind tunnel? There are very large wind tunnels out there. Wouldn't it be very efficient to test new airplanes flying them "on the spot" inside of these tunnels? That is, in free flight - not mounted to a pylon? One could presumably omit the test pilot and remote control them, get excellent visual feedback and have a completely controlled environment. Has this been done? If not, why?
It would actually miss the point of wind tunnel testing. A free flying model could only be subject to air stream in speed and direction so that the forces are balanced. A fixed model on the other hand can be subject to air stream of any direction and speed and the forces measured. It is important to measure the forces under those conditions too.