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Internal frame work

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David Schwantz

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If anyone has pics of an internal frame work for support of airframe, would like to see them. I am using a 12" OD sonotube for the frame, will be glassed on outside, but wondering if I should build frame inside also. Probably fly on an AT M1350W. Thanks in advance.
 

David Schwantz

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Hi Tony, thanks for the pic. But I am hoping mine comes out straight :)
 

kalsow

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But I am hoping mine comes out straight :)
Straight is overrated. :)

That rocket flew just fine:

Actually, we had hoped the external skin -- the shrink wrap they put over boats for the winter -- would provide a bit more rigidity. If you watch the video closely the rocket appears to flex at motor burnout.
 

kalsow

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If anyone has pics of an internal frame work for support of airframe, would like to see them. I am using a 12" OD sonotube for the frame, will be glassed on outside, but wondering if I should build frame inside also. Probably fly on an AT M1350W. Thanks in advance.
I am not a mechanical engineer!

Here's a simple thought experiment. How much does your nose cone weigh? 15lb? If so, under 10G of acceleration that NC looks like a 165lb static weight. Will the body tube standing vertically on the ground hold that weight? Would you stand underneath it? :)

Spiral wound tubes (like sonotube) usualy fail at the seams. A small dent from carrying or transporting a big rocket can be fatal. The primary value of a thin fiberglass exterior is to prevent those dings. If you have a thick fiberglass exterior, ditch the sonotube. It's just extra weight.

I am still not a mechanical engineer.
 

David Schwantz

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Hi Bill, think I have been to that field before. That was a great flight. And I did see it flex.
 

jqavins

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OK, I'm not a mechanical engineer either and I haven't done any fiberglass work. So why am I even writing about this? Feel free to ignore me.

If the fiberglass is done the way I've read then the first layer of epoxy will penetrate the cardboard fibers a little, including into the outer layer seems, and lock it all together. A straight circular column is really quite strong assuming it doesn't buckle. I think a 12" diameter, thick walled spiral wound cardboard tube with a layer of laminating epoxy is not going to buckle under a 165 lb load that's well centered. Yes, I'd stand under it. If I had a reason to, not just for giggles.

If the fiberglass is thick enough to take all the flight loads, the sonatube made a hand form and doesn't weigh enough to bother removing.

Internal structure? I'm not even going to gue... yes I am. I'm not aware of others doing it. I guess it would help prevent buckling, which I already guessed won't be a problem. So my guess is you don't need it.
 
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