Airplanes designed in the 1980s have a radar cross section (RCS)-the theoretical size to which stealth technology reduces an object-of about 8/10ths of a square inch. That's the same as a half-inch metal sphere, a small bird or a large bug, which is still detectable at certain close ranges. Recent technical papers, though, have talked about RCS numbers of 4/10,000ths of a square inch-smaller than a mosquito. The Bird of Prey's signature is very likely in that vicinity.
But why did the Bird need to fly? If it really is that stealthy, there is no point in building a flying prototype for radar tests, because you can test for that on the ground. The answer lies in the multi-toned gray color scheme, particularly the light-toned patch ahead of the inlet, as well as the cryptic references during the unveiling ceremony to "specific LO technologies." The white patch is part of a counter-shading color scheme that minimizes shadows caused by the airplane's shape.
Conclusion, confirmed by senior Pentagon officials: The Bird of Prey is designed to achieve stealth in daylight. Today, the Air Force will not operate its current stealth airplanes-the F-117 fighter and B-2 bomber-in daylight. Though they can elude radar in daylight, their black color renders them easily visible by ground observers or enemy fighters. Bird of Prey engineers could only test the aircraft's visual stealth if the airplane flew. You cannot test this on the ground because the environment is different at 20,000 feet. The air is clearer, the sky is darker and the airplane is illuminated by light reflected from dust and moisture in the air below it.single page