alternate fin materials for LPR?

[bjphoenix]

I was wondering if it is reasonable to use thin plastic for fins instead of balsa. I have an old Quest kit that uses thin styrene, and another old kit that has some kind of thin plastic, maybe the same. If styrene isn't strong enough then what about G10? Is there a weight or flutter problem with something like thin G10?

I'm not sure the exact density of G10 but I took a guess and did some calculations- a set of 3 fins about 2" x 2" x 0.062" would weigh about 1/2 ounce, which seems that it could be significant in some rocket designs and somewhat insignificant in others. Elsewhere I found some 0.031" and 0.047" thick G10.

 

[GregGleason]

What is the max velocity? If you are doing Mach 0.6 and below, paper-skinned balsa should be just fine, I would think. Look for stronger methods if you are going beyond Mach 0.8.

Greg

 

[[POW]Eagle159]

LOL, I used cardboard for fins for my most recent scratch build! :y:

 

[bjphoenix]

What is the max velocity? If you are doing Mach 0.6 and below, paper-skinned balsa should be just fine, I would think. Look for stronger methods if you are going beyond Mach 0.8.

I was asking sort of as a general question. But also I was a little interested since G10 fins would be much easier to make than filled or skinned balsa, and everything small that I make is low velocity. IOW just cut them out, sand the edges, and glue them on. Plus I think thin fins would look better on some models. I don't know if I will ever try this because I don't have a good source for a small amount of thin G10, but I might run across some someday.

Some people dislike painting, I dislike filling/sanding/priming balsa fins.

 

[[POW]Eagle159]

Some people dislike painting, I dislike filling/sanding/priming balsa fins.

I think we all here you on that one!

 

[fyrwrxz]

Back in the day I flew commercial so much that it seemed I had a boat load of those insufferable AOL 'try free' discs they practically threw at you on boarding that always wound up on the table after each sojourn. One rainy day in Washington, I just took a razor saw to a couple and made elliptical fins w/tabs for ttw on a BT-60. Worked well on a c6-5.

 

[GregGleason]

I was asking sort of as a general question. But also I was a little interested since G10 fins would be much easier to make than filled or skinned balsa, and everything small that I make is low velocity. IOW just cut them out, sand the edges, and glue them on. Plus I think thin fins would look better on some models. I don't know if I will ever try this because I don't have a good source for a small amount of thin G10, but I might run across some someday.

Some people dislike painting, I dislike filling/sanding/priming balsa fins.

I hear you on that one. It's not fun.

I have some 1/16" inch G10 and even at that thickness it is still pretty hard to cut. But it's not going to collect dings like balsa, that's for sure.

If you want to try some thinner G10, you can get a 12" x 12" sheet from McMaster-Carr for a reasonable fee:

https://www.mcmaster.com/#grade-g-10-garolite-film/=fg78d4

What you can try is getting some film G10. Cut out two fin shapes from the G10, then cut out two fin shapes from paper. Epoxy the paper between the two G10 shapes and voila! You have your own mini-composite fin. It's a little work, but you are trading one work process for another.

Greg

 

[fyrwrxz]

Greg- you mentioned g10 film-where the heck do you source that at? It's intriguing and expiring minds need to know....

 

[GDJ]

I like Basswood myself. Stronger than balsa, a little more heavy but less than birch plywood. It's a good substitute for Balsa.

 

[bjphoenix]

Back in the day I flew commercial so much that it seemed I had a boat load of those insufferable AOL 'try free' discs

I used to have a lot of old CD's laying around too. I had always been very careful with CD's, thinking they were somewhat fragile and might break if I wasn't careful with them. One day I had an old CD so I decided to see how far it would bend before breaking. I had the CD in the palm of my hand so I just folded it in half like a taco shell. I could bend it until the 2 sides touched and it still didn't break, so that stuff would be plenty strong for fins. You can't get very big fins out of a CD, but for a small rocket you could probably get a full set of 3 or 4 out of a single CD.

 

[GregGleason]

Greg- you mentioned g10 film-where the heck do you source that at? It's intriguing and expiring minds need to know....

fyr

See the McMaster-Carr link below:

https://www.mcmaster.com/#grade-g-10-garolite-film/=fgb2h0

Greg

 

[fyrwrxz]

Greg- Thx mate!

 

[MarkII]

Thin styrene sheet will work fine if you use the built-up method to construct your fins. They will be strong but incredibly light in weight. You can get away with using very thin material over the internal framework. And the nice thing is: you will have no grain to fill!

 

[bandman444]

I'v used old credit cards. Actually hotel keys (don't have the dimpled numbers). They work fine as long as my fin can fit on one. I cut them with some sharp shears and they come out fine.

I haven't painted them but I wouldn't think it would be to difficult.

Plus on one side it is a free paint job!

Bryce "I don't normally fly LP, but when I do, I use credit cards for fins" Chanes

 

[MarkII]

I don't have much experience with using G10 in low-power rockets, but what experience I do have with it has been good. I have one low-power rocket that has fins made from G10. It is my 18mm Platinum Eggstravaganza (contest egg-lofter) from Aerospace Speciality Products (ASP). The fins are average size, I would say, for a 14" long payload rocket that is meant to be flown on B and C motors. Although the quite thin material is rigid for its thickness, the loose fins could be flexed a little bit. Bonding the fins to the tube by their root edges, though, made them more than stiff enough for any LPR and many MPR motors. The residual flexibility is a nice feature of the material; because of it, the fins are quite resilient (l.e., they can absorb shock without splitting or breaking). So I would say that you could confidently use thin G10 sheet for fin stock for low-power rockets.

 

[MarkII]

LOL, I used cardboard for fins for my most recent scratch build! :y:

Several classic kits used die-cut fiber board (aka cardboard) fins. In fact, the very first mass-produced model rocket kit, the Balroc Rock-A-Chute Mark II, featured cardboard fins that were stapled (!) to the body tube.

And don't forget: you can also use paper tubes for fins.