Modify Katana Fin? How to fill in gap?

[JSW]

I have an Apogee Katana kit and am ready to assemble. I like the rocket design a lot - except for the fin profile.

I don’t like that the trailing edge of the fins is pretty much in line with the end of the rocket. Also, the gap looks odd to me - especially near the tip. (see pic 1)



I’d like to cut off part of the trailing edge so that it sweeps more forward. (Of course I’d need to recalc CP.). If I modify the trailing edge, I think it could cause the fin to be weak in the area of the “gap”. I’d like to fill in the outboard gap with something to strengthen. (See pic 2)



The question is: What would be good to use to fill in the gap? Rocketpoxy?

I’ve seen that done somewhere else on the forum, but now can’t find it.

Any advice would be appreciated. Thanks!

 

[neil_w]

How about just cutting a small piece of wood to fit in there? That would be straightforward and strong.

 

[JSW]

Of course, as soon as I post my original question, I found the other post where I saw this done: https://www.rocketryforum.com/threads/zephyr-build-thread-with-quasiglass-tubes.167052/post-2155603

Would this be the right approach:

I’m picturing putting tape on one side of the fin gap, and then fill up the gap with rocketepoxy? Once dry, use wood filler as needed to make the non-tape side smooth?

 

[Rob Campbell]

Cut a balsa plug or plugs to fill the opening. Glue it in with carpenters glue for easy sanding.

 

[JSW]

Wood plugs sound like the easiest way to go.

And maybe if I fill in the gap near the edge, it will look better - such that I don’t need to modify the trailing edge. Retain full strength and no change to CP.

Thanks!

 

[JSW]

If anyone is interested,… here is what I ended up doing:

(1) used a Dremel cut off wheel to cut a groove in the middle ply of each fin



(2) Glued in balsa scraps as filler (wish I had used light ply instead).



(3) Cut off excess balsa filler material and sanded it down.



(4) Cut off part of the trailing edge (for personal aesthetics). Installed in body tube.