Mythbusters Bus Jump Small Scale

dr dodge

i did
nice job

dr

dr dodge

system, pm'd the sensor info
(tried to refrain from shameless plug)

dr

SystemTheory

Tonight the Mythbusters tried to skip a sports car across 100 feet of water. The cars at 1/12 scale and full scale worked best with high velocity and no jump ramp.

The jump ramp caused cars at 1/1 and 1/12 to flip and land roughly nose first, what we used to call an "endo" when I raced motocross. One thing that contributes to the endo motion is the impulse imparted by compression and rebound of the rear spring at the lip of the launch ramp. I think this is what is causing the cars to rotate so much, and it may be a function of ramp angle and length being at the harmonic of the spring rebound. In other words the ramp length might need to be "tuned" to the suspension in addition to considering the weight, balance, and drive torque of the vehicle to get a machine to fly properly. If so some fairly complex physics are involved. In motocross the rider will preload the springs on a jump and use the rebound energy to best advantage. This video (maybe fake? looks real) has a car jumping a short fence successfully using a ramp a bit shorter than the length of the sedan.

http://clipaday.com/videos/redneck-car-jumping

rcgldr

Dave has the answer, perhaps it would be more simply stated that these aren't ramps, just 'level' sections of road with a gap in between. Imagine that the ramp was completed. No ramp would be designed to send a vehicle airborne for the distance covered by the gap in the movie, at least not at the speed the bus was going. The ramp sections are level, and given sufficient grip, a vehicle could probably take the completed version of ramp at 120 mph without going airborne. With the missing gap, the vehicle would start falling as soon as it entered the gap.

SystemTheory

Well, I have caught air on my motorcycle unexpectedly when crossing elevated train tracks at ordinary road speeds! But I agree a road should not have a 50 foot jump built in at 78 mph, so that part of the Myth/stunt is totally busted. In regard to getting a bus to jump 50 feet I watched the episode again last night. Grant says on the DVD release of the movie the out-takes describe (or show) the use of a pneumatic lift at the end of the launch ramp. I suspect it would impart an upward torque impulse on the front wheels to compensate for the downward torque impulse about the rear axle over the estimated time of flight.

diazona

cool, thanks Ideally I try to write something all the cool physics-y myths they do, but I've been missing a lot of them lately because of schoolwork. (Just got one up about "Unarmed and Unharmed" from last week, though, and sometime between now and this weekend I'll do the car skipping)