Tunnel would reflect the radar signals, obfuscating the data. You would also be highly limited in the size of models you can test by the size of the tunnel. To

Tunnel would reflect the radar signals, obfuscating the data. You would also be highly limited in the size of models you can test by the size of the tunnel. To test in flight you'd need a functional aircraft as opposed to a cheap mockup. Further an aircraft in flight has to move quickly to stay aloft, and its exact position and orientation can't be precisely controlled. A model on a pylon stays put exactly where you want it for as long as you need it to.