Fiberglassing boo-boo, need help.

[Murrill]

I've glassed the fin can on several prior rockets, but never the airframe, and now I'm preparing to boldy...er, tepidly...go where numerous people have gone before. I have a PER Honest John and I'm going to take a stab at glassing the airframe. In preparation, I peeled off the glassine layer and cut out the fin slots.

But wait...did I screw up by cutting out the fin slots prior to glassing???

On the PER kits, the fin slots are "open," they extend all the way out to the rear of the airframe. When I cut the slots out, the rear of the airframe flared out somewhat. If I place one of the centering rings in the rear of the airframe, there's a gap of approx. 1/8" between the inside wall of the airframe and the outside edge of the ring.

Obviously, I'm going to have to eliminate the flare when I glass the airframe. But how? Will the process of applying the glass and squeeging out the epoxy force the rear of the airframe back into place? If so, might it squeeze the rear of the airframe so much that it actually ends up compressed into a smaller diameter than was originally intended, so that the centering rings are now too big?

I'm not sure if I screwed up or not. I sure could use some advice from all the glass wizards out there.

Thanks in advance.
John

 

[UhClem]

I don't think you have anything to worry about. Now.

Don't worry about removing the flare while glassing the airframe. It just doesn't matter. Fiberglass normally and then cut the glass out of the slots. Even if you tried to remove the flare while glassing, it will return as soon as you open up the slots again.

But when you assemble the rocket you will have some fun. You will need to clamp the airframe around the centering rings somehow. Unless you add an incredible amount of epoxy and fiberglass, it shouldn't be so stiff that you can't clamp it down.

The easiest way to remove the flare is to glue the centering ring into place before attaching the fins. This way you can just use tape around the tube to clamp it down. It sounds like your fins will prevent using a tape clamp after the fins are attached.

But this does complicate attaching the fins. Foaming the fin can and then another fin tip to fin tip layer of fiberglass should hold everything together even without internal fillets.

 

[Ryan S.]

you could tack a CR in there with enough CA to hold the BT down, glass the airframe (without getting epoxy on the CR) then knock out the CR and build normally

 

[LMazza]

That's what I did. I also cut the slots and then glassed like you. I wrapped a tin can in wax paper and stuck it inside the BT to keep it from deforming. Worked like a charm.

 

[Justin Horne]

I had a similar thing happen. What I did/am doing, is this:
First, cut the fin slots all the way to the end.
Then, build the fins and motor tube out of the body tube, and place fillets fin>motor tube. Then, glue in the motor tube. Then, take 1 inch fiberglass strips from fin>body. Then, a fiberglass strip (~ 3 inches in my case) between the fins. After this, just regularly glass above the fin area. That's what I'm doing. All I have to do is glass above the fins. Worked well for me!

 

[Clay Kremer]

A reallly easy way is to just use a hose clamp after you slide the fins in. It molds the airframe to the aft cr perfectly. I've used that on everything I've built the fincan outside of the airframe and it's worked slick. I'll even use that technique on my 11.5" cluster rocket.

 

[Justin]

It wasn't glassed, but I did a PER fatboy that had that flare too. When I epoxyed in the motor mount and fins, I just wraped a steel wire aound it and gently tightened it until everything was lined up. The wire didn't even mark up the tube too bad when I took it off. It worked well.

Here's a pick of it all glued in.

 

[Ryan S.]

Originally posted by Clay Kremer
A reallly easy way is to just use a hose clamp after you slide the fins in. It molds the airframe to the aft cr perfectly. I've used that on everything I've built the fincan outside of the airframe and it's worked slick. I'll even use that technique on my 11.5" cluster rocket.

great idea, although the rocket I had this problem with, the fins went all the way to the back of the rocket, therefore, this wouldnt work, although it is a very good idea due to the fact that the hoseclamp conforms to the shape of the BT