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View Full Version : Fiberglassing a rocket fin can before inserting it into the airframe



andrewlathrop87
25th July 2010, 05:13 AM
Hey guys again! I am building a Always Ready Rocketry rocket from Randy, called his Basic Blues. It is a 80 inches long, 4 inch diameter, 54mm motor mount with 3 1/4 fins it is also Blue Tube. I will fly it on J's and K's. I am wanting to fiberglass the fins, but building the fin can outside the rocket then covering in fiberglass then inserting in the body tube. Any suggestions on how to do it, since I have never down this sort of thing and brands of fiberglass to use? I am sure some or most of you know the drill on how to best apply fiberglass onto a rocket.

sylvie369
25th July 2010, 12:37 PM
You can glass the fins two at a time to the motor mount tube and to each other, with a rectangular piece of fiberglass cloth laid across them and epoxy drizzled on. I usually cut the fins in a way that allows them to fit into the centering rings at either end so they stay put on their own while I'm doing it. Sand everything so it's rough, so the epoxy can get a good grip.

Don't use too much epoxy, and with J and K motors, you'll be fine with pretty light glass cloth. This is the wrong end of the rocket for weight, and it doesn't take much to give you more strength than you'll ever need.

jungmann1
26th July 2010, 12:51 AM
Just how fast are you planning to push this thing, Andrew? Tip to tip glass is probably overkill unless you are going for a speed record. This type of treatment is best when you have high aspect ratio fins where the aerodynamic forces and impacts from landing have a long lever arm to act on. You might be better off just using a hefty epoxy internal fillet with some chopped glass mixed in to add strength. Sounds like a great project; keep us informed. J.

blackjack2564
26th July 2010, 04:44 AM
I am assuming the fins are wood.

Glass the fins first with 6 oz. cloth.
Drill holes on each side of fin slots.

Make sure centering rings butt tight to front and back of fin tabs.
Tack fins into position.
Inject mixture of chopped carbon fibers and epoxy through holes to do internal fillets.

Then do external fillets of West 406 colloidal silica and epoxy mixed to peanut butter consistency right over the holes. Bam....your done.

Simple, easy, and strong. These fillets will NOT fail. Just worry about the rest of rocket.

Check out any of my Crazy Jim build threads to see how it's done. You can fly any motor that will fit in your rocket safely without worrying about the fins coming off.
Whether they flutter will be determined by how many layers of glass you put on the fins first.

How the airframe holds up is out of my hands. But you can bet your bottom dollar there will be fin stubs left on your motor mount. LOL

Handeman
29th July 2010, 01:29 AM
Crazy Jim is right about the fillets.

I don't think you would even need the glass on the fins, considering the kit and fin shapes, but that would definately make it bullet proof. I wouldn't bother with the tip to tip.