Originally Posted by
majicbar
This video is of a NASA chase plane following either the X-45. or X-47. The contrail is a dead giveaway that it is ours, not the UFO claimed by the poster at YouTube. The chase is a F-18 and the contrail for it is at least twice as heavy and starts closer to the one being followed, this means that the exhaust was not as hot, which fits with the stealth nature of cooler exhausts. My guess is that a much better video exists of this chase, it would not have been used because the true nature of the object would have voided any chance of calling it a UFO.