Ordinary Nothing

I originally saw an article about an actual major car manufacturer announcing they’ll install these sort of things, but I can’t seem to locate that link. So here’s a link to an announcement by someone that wants to make these external airbags.

I assume people must have run calculations, simulations, and tests, before going on with these things. Try as I may, however, I just can’t see how this would have a practical benefit.

The idea behind this is to open an airbag outside the car, so that if the car hits a person, the person will collide with the airbag. Like an internal airbag, but for the pedestrians. This is supposed to make for a softer impact, and reduce injury and risk of death from the collision.

But the cases are totally different. For a driver inside a car, that collides into something hard, the logic is simple. The car stops, the driver still has momentum so they will continue to move forward, and so collide with the wheel/windshield/whatever inside the car. So an airbag pops out, and the driver makes the collision with something soft, that gives a little under the pressure of the collision, thereby dissipating the driver’s kinetic energy over a longer time period. This results in the driver being less squashed and broken.

But for someone on the outside?!

First of all the car can’t detect the collision before the collision occurred (Special precognition chips? Surely if someone had those the first use wouldn’t have been for airbags…). This means that anything that would happen, would do so once the pedestrian was already partially hit, and pushed backwards.

If the airbag should touch the pedestrian directly, against the leg that hit the car’s front bumper, it must move faster than the car does. It may be softer, but it can’t stretch the total contact duration to more than it was without applying more force. If contact is to be with the bag and not the bumper, it must move faster, and keep moving faster.

This should result in the pedestrian being hit harder. So the leg will break more seriously, or they will fly backward faster and brake more bones on the road/sidewalk.

After all, if it could work for a car hitting a person, it should work just as well for a car hitting a car. Anyone manages to imagine to cars crashing headlong, spurting airbags at each other, and coming out less damaged as a result? Anyone manages to do that without bursting out in laughter? If so, start working on it, every car owner will want one installed to protect their cars from accidents… Darn, actually that could work… I should write a patent.

Or maybe it’s to prevent the initial head injury, then? When the bumper hits the leg, and the car keeps moving at a fast speed, the pedestrian will effectively tilt, until their upper body will collide with the front windshield or the engine hood.

This could be it, to some level. The damage here can be more dangerous. And the airbag actually has some time to deploy before coming in contact with the pedestrian. But from what I understand, the bag either comes out from near the bumper, or the car’s hood opens with an airbag popping out of it.

From the bumper, it again doesn’t quite feels right. The airbag comes from the point of impact, going up, while the pedestrian’s upper body goes along the car. It means that the person will not crash into the bag, but rather the bag will scrape them from the knees up and push them out. It may be better than impact on the car, but it can also be much worse. The person will again fly off of the car at a higher speed than they would have originally, only they will start the process being thoroughly bruised.

The hood springing open with an airbag beneath it can work. It’s closest to the original airbag scenario, which is proven as (mostly) working every day. I’m just not sure about the speed ranges in which it’s applicable. Popping and filling a bag at a high speed can be done. Popping a large metal plate at an extremely high speed is more problematical. And if it’s not very very fast, the poor person will get banged by the hood as it opens. They’ll get the original impact force concentrated on a smaller area (the point of impact with the hood’s edge), meaning more damage. And in addition they’ll get the damage from a metal plate going fast in a different direction. All that before the bag comes along and pushes them away.

I don’t know. Maybe my kinematic first impressions are wrong. If it can be done for certain speeds and reaction times, maybe it can be done for all of them. I’m still very uncomfortable with the idea. If a car hit me, I’d prefer it if it didn’t go on to continue attacking me further. It would be bad enough as it was.

December 16th, 2004 at 22:56 EET | Categories: Cars | Track comments. You can skip to the end and leave a response. Pinging is currently not allowed.