Fin Can Attachment

[mccordmw]

Messing with blueprints on large scale rocket. I'm wondering... Fin can, slide in and bolt on, or epoxy it with fillets to the aft airframe? I like the idea of being able to bolt it on so I can change out fin geometries and motor mounts if I want to experiment. Then again, how often do people do that?

And is there more of a concern about fins fluttering when bolted on? I suppose it would hold on tight enough.

 

[Binder Design]

What kind of fin can?

 

[fyrfytr310]

The bolting won't impact flutter itself, just the fins ability to withstand those forces.

FWIW (probably not much) I haven't done a bolted can and would personally only consider it on an aluminum design. I like epoxy

 

[mccordmw]

What kind of fin can?

Sliding in a motor mount with fins and axial supporting fin tabs. It's for an 8" diameter rocket with a 98mm motor mount. I kind of prefer the look of non-filetted fins for something that's based on a military model.

View attachment 8 inch scratch MEADS PAC-3 L3.ork

 

[Binder Design]

I can say without a doubt that a properly sized bolted on fin can will be stronger than anything you can epoxy on. The trick is the sizing. Too tight and the act of bolting it together will deform the tube. Too loose and you lose all the extra strength and you can get flutter because the fin roots won't be clamped tight against the tube. You see, when you bolt in on, the airframe tube itself then becomes a structural member and actually stiffens the whole assembly.

The trick is proper sizing. That can be a huge headache with a lot of math. Most people don't realize how slight the difference is between a good fit and an unacceptable fit. Like a few thou can make a huge difference.

 

[mccordmw]

Thanks! I'm not skilled enough to scratch build something with such tolerances. Though it means I'll have less flexibility to swap out fins or mounts, I'll epoxy on the mount and fins to be safe. I can always swap out the whole booster section, motor mount and fins and all, if I want to experiment.

I'll focus on building something that's safe first.