Selling spring landing gear

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choppergirl

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Just out of curiousity, is fiberglass springy? Or is there some kind of metal inside?

I always thought fiberglass cracked and splintered if bent too far; if you could bend it at all... and you put a 1,100 lbs aircraft on it...? Something I don't know.
 

meglin1

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There were cases when the landing gear of the aircraft is completely unbent spring (480 mm deformation). The photo deformation of 140 mm, the force - 2000 kg.
Fiberglass, unlike metal tends to dampen energy - hysteresis.
 

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choppergirl

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I always thought there was something else inside diving boards. But yeah, fishing rods, got it. Very crazy bendy without breaking. Didn't know that about Corvette auto springs.... that's crazy. I knew the bodies were fiberglass. I've done fiberglass repair on a friends car, its easy. Now you got me wanting to replace my heavy landing gear with fiberglass (maybe someday way down the road, long after it's flying, and I'm gung ho to extend its glide ratio).

At one time we had a huge roll of fiberglass here on the farm, the size of a round cotton bale. I have no idea how my dad came into it, or where it went.
 
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Victor Bravo

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Vladimir, if that is you in the photo where the spring is being compressed in testing, you should be wearing some sort of a protective face mask. If that landing gear ruptures you would possibly get a face full of fiberglass shrapnel. A very poor risk-reward choice is shown in that photo. High risk, very very little reward.
 

meglin1

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Thank you!
No, it's not me :).
The colleague relaxed - he never had explosive destruction.
 

lr27

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I think I'd want to be in another room or hiding behind something big, steel, and heavy, wearing a face shield. But I used to work with someone who'd use one of those offset circle cutters on a milling machine, with the feed rate so high that little chunks would cross the room and fly out the door. The Whole Earth Catalog used to have an article recommending wearing a big phone book over your chest when using one of those things.

I think the figure of merit on something like landing gear material is how much strain energy* per unit weight you can get without breaking. I think you can approximate that with the breaking stress** squared divided by the elastic modulus, divided by twice the density. There may be a constant in there I'm forgetting. Also, the density has to be with the same length unit as the other two numbers.

If I'm not mistaken, if you had a unidirectional carbon fiber layup, with a breaking strength of 200kpsi and an elastic modulus of 20 mpsi, strain energy would be 1,000 in-lbs/in^3 or I guess you'd say lbs/in^2. For a uni e-glass layup with, say, 100 kpsi and 6 mpsi, you'd get 833 lbs/in^2. I would have guessed the fiberglass would be slightly better, but maybe my figures for stress and elastic modulus are off a bit. Easily converted to strain energy per lb. by using the density.

Knowing the elastic modulus and the breaking strength, one could vary the thickness of the landing gear to give the right amount of deflection per given load.

Surely someone will call me on it if I'm wrong.

Choppergirl:
I suspect it would be best (or lightest, at least) to use a layup that's mostly unidirectional.

*I don't know if my definition is the official one. Seems like, in the extreme, there might be significant three D effects. Another figure of merit is probably the damping, but my guess is that comes mostly from the tires, friction, etc. At least for airplane landing gear.
**or, it probably makes more sense to use the allowable stress.
 

meglin1

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Each spring is tested with a load of 1250 kg. A loading and test protocol is compiled for each spring.
 
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