I think it's not so much the appearance of the craft that makes this case a classic UFO case. It's the way it took off.
No sound, no heavy impact on its surroundings, yet gone in the blink of an eye. (Note that Adrian Bustinza witnessed a similar take-off on the third night.)
To my knowledge there are two occasions in which the acceleration performance of UFO's have been analysed:
- Paul Hill's own sightings (
http://en.wikipedia.org/wiki/Paul_R._Hill#Hill.27s_second_UFO_sighting)
- An analysis by Dr Bruce Maccabee (
http://brumac.8k.com/Acceleration/ACCELERATION.htm)
Both come to the same order of magnitude: 100 g's (!). This is a lot faster than the eye can follow (if you watch something accelerate unexpectantly at 10 g's or more you already are not able to follow it).
Our current propulsion systems (including that of the F117) are all based on the same principle: You throw something out in one direction (hot exhaust gases for instance) and your craft travels in the other direction. If you want to accelerate with 100 g's using that principle there would be no Rendlesham Forest left...
But if you would be able to use
another principle, one that is out of reach for our current understanding of physics, you could be in business. A candidate for this principle would be a local distortion of space/time in the near vicinity of the craft. This would make the craft "fall" in any direction you would like, and because the craft is "falling" you would not even feel acceleration forces. Such a local space/time distortion is more or less the same as applying an "anti-gravity field" (since gravity can be modeled as distortion of space/time).
(A nice analogy is the local air pressure distortion we apply around the wings of a plane to make it fly. To someone who is unfamiliar with this principle it is hard to understand how such an enormous mass can be lifted without applying an enormous amount of thrust. But is does not primarily fly due to thrust but due to a local difference in air pressure in the vicinity of the wings.)
So I don't think it was a man-made experimental craft. Not because of its appearance but because of the way it took off.