Friday, June 27, 2014

Revisiting a Disastrous Car Jump Attempt


Last month, we took a look at a spectacular crash that came about during Guerlain Chicherit's attempt to set the world's longest car jump record. A new video detailing some of the back story, preparations, and shocking in-car footage of crash is now available. Although Chicherit talks at length about the complex calculations he and his team performed in preparation for the jump, he doesn't explain why he thinks things when so wrong. There is, however, a fleeting clue at the 7:54 mark in the film.


The clip is slowed quite a bit at that point, but it appears that the left rear tire is not turning.

The heavily modified Mini he was piloting is a four-wheel-drive car, so if one wheel isn't turning, then none of them are turning. We decided to do a little experiment to show what happens when the wheels stop for a car in flight.

Here's brief video of the experiment we did using one of my daughter's favorite toys - a remote controlled car. We suspended it by a string, started the wheels spinning, then let them stop. You can see for yourself what happens next.



The slow motion portion of the clip makes it particularly clear how the angular momentum of the wheels is shared with the vehicle as a whole. In order to conserve angular momentum when the wheels stop, the little car begins to rotate forward, just as the Mini did for Chircherit.

Have a look at the side view of the jump recorded by a spectator. When the sound of the engine cuts out, the disastrous forward roll begins.



It's not clear why the motor stops. The engine may have spun too fast, leading to an internal failure that caused it to seize up, an automatic fuel cutoff might have kicked in, or maybe in the excitement of the moment Chircherit took his foot off the gas (or perhaps even hit the brake) in mid air.

In any case, despite his talk of the complicated math that went into the record attempt, no amount of pre-jump calculations would have saved Chircherit. You don't have to do any math to speak of to know what conservation of angular momentum will lead to once the wheels and engine stop turning.

I'm guessing that the next time someone tries this, they're going to have to set up a throttle control system that ensures that the wheel speed is set once the vehicle leaves the ground. A more clever solution would be a system that adjusts the rotation of the wheels to precisely control the orientation of the car in the air. It could speed the wheels up to lift the nose or slow them to push the nose down, and ultimately ensure a perfect 4-wheel landing every time.



2 comments:

  1. I watched the accident, it was awful. However, I think the problem that caused the accident is not located in the engine which is in the wheel or axle, similar to your experiment so. Don't know what solutions to avoid similar situations in the air?
    P / S: The car of your daughter very beautiful:)

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  2. A good brief video Buzz.
    I agree with you that they're going to have to set up a throttle control system that ensures that the wheel speed is set once the vehicle leaves the ground and adjusts the rotation of the wheels to precisely control the orientation of the car in the air.
    But do you think that it's very difficult ensure a perfect 4-wheel landing every time?

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