Cracked Fin 🙁
While I flew a good number of rockets on Sunday, a notable exception was my "Not Your Big Daddy" which has flown every CENJARS since July. Why not this time? Because when I pulled it out of my rocket carrier (grey plastic box), I noticed one of the fins had a hairline crack, and I did not have glue with me to make an emergency repair.
So, I came back home tonight and after doing some googling, hit it with some thin CA, right into the crack. After that dried, It seemed fairly sturdy, but, anything worth doing is worth over-doing, so, I sanded it, I mixed up a little bit of 30-min epoxy, will let that dry until Wednesday, (which is when I'll next have time to work on it), and then some light sanding again, and some touch-up paint, or that is the plan.
But before I proceed, any other ideas? I mean, short of laying down fiberglass? And don't actually suggest that, because I'll do it.
Instead of fiberglass, you can use tissue paper. Regular paper works as well. Tissue paper is a little thinner. Roughen the surface a little, spread glue, spread the paper, and add a top coat of glue.
I did pretty much as you said - glued it, then put down some epoxy over the seams. You can tell something happened since I didn't take too much time to smooth it out, but it is strong and has flown a few times without incident (my Estes Executioner - same as the big CENJARS rocket I flew Sunday). Just a matter of how much time you want to spend making the repair look pretty, but I think what you did will hold up.
Brian, can we assume this is a balsa wood fin? If so, fiberglassing it is overkill. If it was balsa, your CA fix is probably enough. The thin CA soaks into the balsa and will adhere the two surfaces well. FWIW, I saturate my balsa fins, both sides, with thin CA. It binds the balsa fibers together making the fin significantly stronger. I then sand the surface with the orbital sander and 320 paper to a smooth surface finish. In most cases, it finishes better than with most balsa fillers.
If you put epoxy on the joint, you're mostly only adding weight. It also depends on the epoxy. RocketPoxy is a good epoxy for filets and, in volume, has great strength. 30-minute epoxy (BSI?) has great bonding strength but for volume strength, it's questionable. You'd be best with BSI to mix it with micro-balloons.
If you want to replace the entire fin, let me know the thickness of the balsa (1/8 | 3/16). I very likely have a plank in my stash you can have. When Jackson Hobby closed, Frank (the owner) gave me most of his balsa stock so I'm rather well-endowed with no-cost balsa.