Shear pin distance from fiberglass tube edge

[Spurkey]

When placing shear pin holes, how far away from the end of a fiberglass tube should they be so that they don't risk tearing out? Before you say "just put them in the middle of the shoulder", assume I don't have a shoulder and need to make one. I bought a perfectly good 2.6" MadCow Honest John and did this:



The nosecone isn't filament wound and I'd already had problems with the edge and the tip chipping, visible in the photo, so this may not turn out to be that wise of an idea in the end, but I'm kinda committed now. For those of you that remember Darrell Mobley's Estes HoJo he had problems with drag separation which I would like to avoid with mine. Advice would be appreciated.

 

[AdAstraPerAspera]

I'd guess that you should be good with an inch or less, I wouldn't take it closer than a half if it were me. But honestly, if this were my project, I'd line the inside with a short piece of the fattest tube I can fit in there and use both a tube and a coupler inside to make the separation point. You could probably use 3 inch switch bands and a cut down coupler, all filament glass. Drill access holes that the shear pin heads fit through in the cone and actual shear pin holes as far from the edge as you can in the inner tube and coupler. This actually looks like an awesome way to make this thing dual deploy. I think a Ho-Jo just moved up my wish list...

 

[Steve Shannon]

Mine are about 1/2 inch but the fiberglass is so much stronger than the force required to shear nylon that there's no reason to fear tearing the g10.

 

[Rocketjunkie]

Fiberglass is far stronger than nylon shear pins. Anything greater than the diameter of the hole will work fine.

 

[AdAstraPerAspera]

Mine are about 1/2 inch but the fiberglass is so much stronger than the force required to shear nylon that there's no reason to fear tearing the g10.

It's not G10, that's the thing. It's a fiberglass layup from a mold. You probably want a couple weaves of the fabric between the shear pin and the edge to prevent the composite from coming apart.

 

[mccordmw]

I never targeted a specific distance. I checked my rockets and they all are an inch from the edge for paper and fiberglass tubes. If you're really worried, you can also epoxy a strip of steel or brass sheeting on the inside to act as a cutter plus give a little extra strength.

 

[AdAstraPerAspera]

you can also epoxy a strip of steel or brass sheeting on the inside to act as a cutter plus give a little extra strength.

This is an excellent plan.

 

[Steve Shannon]

It's not G10, that's the thing. It's a fiberglass layup from a mold. You probably want a couple weaves of the fabric between the shear pin and the edge to prevent the composite from coming apart.

Ahhh, I see. I like your idea of using an internal tube and coupler, or a patch of G10 or metal.


Steve Shannon

 

[Nytrunner]

Second the brass strips. I've found them at Lowes occasionally (by the furniture fastener drawer)