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# My question is about air pressure and using it as a crumple

### Customer Question

My question is about air pressure and using it as a crumple zone for a crash resistant vehicle (http://www.flexobile.com/). I need some basic answers before I can move ahead with the design. And I am also looking for ongoing assistance. The underling physics principle has had an uncanny way of designing itself into a very natural and simplistic construct. This is the first item that the obvious answer did not fall from the infinite universe. So keep a look out for the absolute answer!

www.flexobile.com
Air pressure testing www.flexobile.com/airflex

Initial Questions and Assumptions

The parameter of the initial test is a 1500lb vehicle at 22mph with a 12 inch crumple zone. This impact will have 24285ft/lb of force. (enter data at http://hyperphysics.phy-astr.gsu.edu/hbase/carcr.html to confirm)

Although a truncated pyramid shape is desired, it may be above our prototyping ability (AKA’ Money). So let’s figure on two cylinders extruded 14 inches with a diameter of 15 inches that will give us 353 sqin of surface contact. So if I understand all of this correctly, a surface area of 353 sqin with 69 psi will provide 24,000lb of force, enough to mitigate the impact force. Building a device to handle 69 psi or higher seems well within reason.

Question #1 (partly rhetorical)

What is the initial PSI required to end up at 69 PSI after compressing said cylinders from 14 in to2 inches (12 in crumple zone).

(Or do I benefit from the work being done to compress the air. In a sense each inch of compression should be subtracted from the impact force. IE: if the initial PSI was 6 lbs. The surface are of 353 will subtract 2118 lbs from the impact force. And each inch of compression (at 6 psi) will do the same ie: 12 inches of compression times 2118lbs provides 25,000 ft/lbs ( 6 psi should be easy prototyping) (Keep in mind that I am aware that I am stupid and very aware of the fact that I don’t know what I am talking about. But that fact hasn’t gotten in the way yet.) So, what is correct way of looking at this problem and what will it take to catch the 1500 lbs vehicle traveling at 22mph with a stopping distance of 12 inches and bring it to rest.

Question #2 (only if the second assumption is true or close to question one)

So far the design includes a pressure relief valve to maintain PSI and a blowout valve to prevent recoil. I have failed to validate these devices during testing mainly due to a leaky manifold. Air pressure is slippery stuff. In either case i'm not sure if the current valve system will scale up and be practical.

So the ultimate question, approximately how much air needs to be released during the .5 to .1 sec collision and what would be the size of relief valve to achieve this?

IE: how many 1 inch pressure relief valves will be required to allow the necessary volume of air to escape to maintain an approximate PSI? (Anywhere in the ballpark will do.)

The Blow out valve

As you can see in this full scale test, the crumple cans worked perfectly with zero recoil from the wall. A valve is needed that will blow when the PSIs start to decrease from max PSI preventing recoil. The problem lays in the two facts, max PSI will always be an unknown variable and the limited duration required to react and release the volume of air necessary.

Can you suggest an air circuit and valve that can meet the requirements?

Alternate concepts so far:

Pressure sensor with an Arduino circuit board with an air valve solenoid. (too slow?)

Rotary vane compressor (operating in reverse) with a braking system to control pressure (Interesting)

Turbine fan or torque convertor (Too far out there?)

In conclusion

The device is more for vehicle crash worthiness and reusability than passenger safety so the impact G’s can be higher. The purpose it serves for the passenger is to allow for initiation of rotation, and most importantly to allow for the transition of the passenger’s head to below the axis of rotation. Keep in mind that you are weightless as your seat is pulled out from under you as your body follows a cycloidic path in effort to avert conversion of potential to kinetic energy. One more design note is that, final requirements calls for engine/trans force struts to be connected to the very front of the crumple zone. Consider the fact that a 3000 lb vehicle with a crumple zone of 1.5 ft has the exact same impact force of a 400 lb engine/ transmission with .02 ft crumple zone traveling at the same speed. Managing this energy conversion (potential too Kinetic) will allow us to balance forces with the oncoming vehicle. And wait until I tell you how it performs on a rear impacts, it will blow your mind.

As I mentioned this vehicle has designed itself, all I had to do was ask the right questions. I know the simplistic innovative answer is there.

Appreciate any help you can give, since I will drive this into a wall.

Ed D
Submitted: 1 year ago.
Category: Math Homework
Expert:  mijcar replied 1 year ago.

mijcar :

It's late at night that I'm reading this, so I won't commit to any of the mathematics other than to say that your reasoning sounds good.

mijcar :

I see a few problems and I see one solution.

mijcar :

Problems: In order to work in "real life" you would need the devices to make contact with whatever the vehicle was colliding with. But say for example, a vehicle collided with only the right rear of the vehicle ahead. This would diminish contact points and reduce the mitigating action.

For rigid compression as you describe, effectiveness requires straight line collision. Shear angles would have the effect of crushing the device, perhaps before it can absorb the impact: think of the difference between stabbing with a pencil directly or at an angle to its length.

mijcar :

Solutions: Semispherical shapes might handle shear stress the best.

mijcar :

And one other solution: Think heart chambers. Blow the compressing material (air, fluid, whatever) through a one-way valve into the force-easing chamber which will widen laterally instead of forwards and back. The valve will prevent rebound. Something like this should be embeddable in your design, even a series of such chambers in miniature.

mijcar :

Since I am unable to contribute anything beyond this, I will opt-out after this comment. But if something I said is really useful, you can always come back to this and accept it. :-) Good luck to your, Ed; I hope you succeed.

Expert:  mijcar replied 1 year ago.
Our chat has ended, but I have opted out. Feel free to ask me questions if you wish, but another expert will be able to reply and answer your questions.mijcar41084.286958912
Expert:  Josie-Mod replied 1 year ago.
Hi, I’m a Moderator for this topic and I wonder whether you’re still waiting for an answer. If you are, please let me know and I will do my best to find another Professional to assist you right away. If not, feel free to let me know and I will cancel this question for you. Thank you!
Customer: replied 1 year ago.
I would like to keep the question open as I did not get a full answer. Is there anyway I can give mijcar a partial payment with out closing the ticket?
Expert:  mijcar replied 1 year ago.
I really appreciate the thought, but there is no need to give me anything.

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