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Name: Don
Status: Other
Age: 40s
Location: N/A
Country: N/A
Date: N/A


Question:
I am a Weight Reduction Engineer at Lockheed Aircraft. One of my fellow worker suggested using helium in the tires as a 3 lb savings. After I finished laughing I realized he was serious. I have included his original E-mail to me. Questions Will the helium stay in the tires and how much weight do you see this saving.



Replies:
Don,

I was teasing you a little when I suggested using Helium in the tires.

A little closer but still dirty look seems to indicate that over three pounds is possible per ship set. Dirty because I do not have all the numbers exactly and made some guesses.

The key is the tire pressure is 247PSI (almost 17 atmospheres) for the main and 160PSI for the nose. Helium has a molecular weight of 4 and I think air has about 28 . about a factor of 7.

Main Tire
Inner radius 8 inches
Outer radius 13 inches
approx. thickness 8 inches
air density .0765 LB/ft**3
Helium density approx. air density/7
pressure 247PSI (about 17 atmospheres)

John Moore


Really interesting concept. I am confident that your buddy who suggested Helium in the 1st place has calculated the weight difference correctly. The Helium will stay in the tire, stays in a balloon. My concern would be economics and utilization of a rare commodity. Helium is rather expensive and not readily available in all parts of the world.

An infrastructure would have to be established to pump-er-up, this might be more expensive than the loss in weight.

Myron


Yes it would work but may be an expensive alternative, large aircraft use nitrogen in the tires so why not use helium. The exact effects would be hard to predict just because in my head I was picturing what happens to a helium balloon after a couple of days. Maybe fill a inner tube up with helium and measure your weight reduction versus another filled with air and see how long it stays in there. I am not sure anyone would have a specific answer for your question without carrying out tests as mentioned above.

Good question though, made me think!

Baldwin


I have handled gaseous and liq He for many years and extrapolating any performance from other gases to He is a high risk operation. It always seems to have some surprises. Possibly because it never quite forgets that it is a quantum mechanical substance -- superfluidity etc.

I think there are a number of factors that would have to be examined and tested thoroughly.

First, the concept of the size of a rare gas, i.e. He, Ne, Ar, Kr, Xe becomes itself a little squishy and depends upon what the experimental criteria are. The classical Van der Waals constant 'b' in the eq. of state (V+a/V^2)*(V-b)=nRT is probably as self consistent as any other criterion, yet the value of 'b' is: 0.02370, 0.01709, 0.03219, 0.03978, 0.05105 cubic liters, respectively. Look He is LARGER than Ne!!! This has to do with the shielding, or lack of, in the 2S state of Ne with 10 protons vs. only 2 for He in the 1S state, but nonetheless, it's a surprise.

Second, helium diffuses very rapidly through rubbery materials -- the cause of the short life of helium filled latex party balloons. Aluminized Mylar is much better. But this could be a problem if tires kept "going flat".

Third, helium diffuses readily into some metals. This could be important, if it causes embrittlment.

Fourth, a subject about which I know nothing, but what about acoustic effects? Do shock waves develop in tires upon touch down?? This could be a real "banger"!

Vince Calder



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