Jack is spot on re the Budweiser Rocket. The ThrustSSC research (data captured from rocket models at supersonic speeds to validate CFD analysis) indicated that there would be a double sonic boom and, if the conditions were right, a visible shockwave. This is exactly what happened when SSC made supersonic runs. In addition, the residents in Gerlach had their windows rattled and the detached shockwave some 40ft in front of the car ploughed up the desert surface to a depth of 2 or 3 inches before the car got there. On a couple of runs, the car was travelling faster than the wheels were turning because of this ploughing affect. None of this happened on any of the Bud runs in any report that I've seen. I've written about this myself but the best summary of the evidence that I've seen is by Don Baumea - see link below.
http://www.roadsters.com/bud/To clarify some of Don's conclusions made before SSC ran, it's worth sharing some thoughts based on the research that Ron Ayers had at the time and which have since been confirmed by what he learnt from data captured on the actual runs. Put simply, the shockwave get compressed beneath the car creating an asymetric pressure differential pattern above and below the car. In the air, the shockwave moves backwards more or less equally around the circumference and length of the plane. On the ground, the cone is squashed flat, and rather than bouncing back trying to re-establish its cone shape as many had predicted, it accelerates in the limited gap between vehicle and ground trying to get out. On SSC, Ron reckoned that at Mach1, the air at the back of the car was being pushed out at around Mach2. So, the pressure differential - in front of and behind the now asymentrical shockwave - is also asymetrical above and below the car. Ron predicted that without a tail to deal with this and keep the back end planted, at around Mach 0.9 this pressure differential would cause the tail to lift. The tail did its job and the car worked.
Interestingly, Craig's car (without a tail) exhibited exactly this behaviour when he damaged it at Black Rock in 1996. He said his speed was around 670mph - about Mach 0.9 on that day. In the latest design of the car sold to Fossett, he has a tail between the rear wheel spats.
Even more interestingly for this thread, the Bud rocket (also no tail) did exactly the same thing and there is a good pic of it with the back wheels off the ground. In that pic you can also see the FIM timing traps. Guess what speed was reported by them when Don Baumea was doing his research? 666mph or about Mach 0.9. Coincidence - maybe? The stories about the ground radar are well known and again I refer you to Don's article.
Obviously, you're free to draw your own conclusions. Mine are that based on the evidence, I don't believe that the Bud Rocket went supersonic even briefly. On the other hand, there is conclusive evedence that ThrustSSC made a number of supersonic runs; runs on which it travelled at an average speed in excess of Mach 1 for the whole of the measured mile in each direction.
And by the way, today is the 9th anniversary of those record breaking runs.
Robin
