Fin size/ material question

[f16fan12]

Hi, I'm planning to scratch build an ~ 80 inch rocket (around 50 oz, powered by a 29mm hobby and 2 24mm), and I wanted to cut the fins myself. I'd like to use some kind of wood, but I'm wondering:

a. what kind of and thickness wood would be good?
b. what would be a good size for that wood?
c. would a low-power dremel with a cut-off wheel work for cutting? is that precise?

Also, around what length of shock cord do you think I need? I currently have a 48 inch parachute, but do you reckon that would work with this?

Thanks a lot,
Jesse

 

[TeenRocketNerd]

I would probly use 1/8" plywood.

I don't know how straight a dremel with a cut-off wheel would be, I think it would be hard to cut for fins the exact same with something like a dremel. I might try a hobby saw (like what estes used to recommend to use to cut their fins) if a scroll or bandsaw isn't available. You probly *could* cut the fins with an exacto knife and a number 11 blade, but that might take a while with ply.

HTH

 

[TeenRocketNerd]

using this
your descent rate is around 16 ft/sec (16.28) that would seem about right to me, if you're flying on tall(ish) grass, I would say that would be lovely.

 

[jj94]

I would also use 1/8 inch ply. I doubt the a dremel cut-off wheel will work well. I tried it and it just burnt the wood. Try looking for the mini saw attachment. That looks like it'll work for you. If not, just use a razor saw.

 

[Bohica]

Huh...I thought just about everybody owned a jigsaw...

 

[f16fan12]

I would like the mini-saw (as well as the circle cutter, for another part of this project) attachment, but I have the smallest dremel available. It's 4.8V and I don't think the bigger attachments like the saw would fit on this one.

I guess I'll be doing it by hand then...

 

[f16fan12]

I've attached the rocksim file for this rocket. What do you think of the fin size?
Also, would having it split between the body tubes be a reasonable thing to do? Is there much danger of the two parts banging together after ejection? I guess it would depend on where I put the parachute on the shock cord...

And would the combined ejection charges of two F-21s and one G-64 (or G-33) be enough to pressurize the interior? This rocket seems pretty long.

Thanks for the help.

 

[roadkill]

Yea,

1/8" birch ply sounds good to me too, unless you wanna save yourself some sweat and order G-10 pre-cut standard fins from PML. They carry a huge selection, should have a few choices to fit your project.

I use a combo of a cordless jig saw with fine blade and a cordless skil saw with a paneling blade... Dremel just won't cut it...

Ok, that was a bad pun, so sue me....

 

[Bohica]

Originally posted by roadkill
I use a combo of a cordless jig saw with fine blade and a cordless skil saw with a paneling blade... Dremel just won't cut it...

BWAHAHHAHAHAA!!!

 

[astrowolf67]

Originally posted by f16fan12
Also, would having it split between the body tubes be a reasonable thing to do? Is there much danger of the two parts banging together after ejection? I guess it would depend on where I put the parachute on the shock cord...

You'll definitely want to split it in the middle. An 80" long rocket will be a total pain to transport, and prep, without damaging it. I built my Mean Machine to split in the middle, and used about 12 feet of elastic shock cord, with the chute attached a couple of feet from the upper section. Inside the coupler for the upper section, I also installed a ply bulk head. Much less space to pressurize for ejection. With it split in the middle, and a bulk head in the upper section coupler, you should be just fine on your ejection charges.

You won't be able to cut your fins with the Dremel. I have a 7.2v cordless and it's great for sanding, drilling, or polishing, but doesn't last long at all when cutting. A cutoff wheel on wood, doesn't do well either, it burns more than it cuts. You can get a cheap jig saw, and some fine blades that will do a much better job, or just get a small coping saw. Which ever method you use, cut just a bit over size, and sand down to final size. You'll get a much better finished product that way.