This reminds me a little bit of the "downwind faster than the wind" discussions that have been going on over the past year in the Amateur Yacht Research Society. Very smart people on both sides of the argument would come up with very detailed explanations of why it was or was not possible, both equally certain of their position. Somebody recently built a small machine with propellor driven wheels and sent it downwind - any guesses? - yes, faster than the wind. He promises to report on additional tests.