L2 Carbon Fiber & Fiberglass

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Mainless

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Last edited:
Fiberglass kits go on sale, from time to time there are good L2 options for two digit prices. Carbon fiber is a dream, at least to me. Except that fiberglass is so good I rarely dream of better.
 
watermelonman said:
Fiberglass kits go on sale, from time to time there are good L2 options for two digit prices. Carbon fiber is a dream, at least to me. Except that fiberglass is so good I rarely dream of better.
Click to expand...

Once you get a taste of carbon fiber you wont go back to fiberglass.
 
Mainless can you please post a picture of your design. My surface pro is having wifi issues and I cant access the .ork file.
 
Yeah, Mainless...

You might want to edit out the expletive before the moderators do it for you.

Carbon is nice. But expensive.
 
Mainless said:
Im going to use the through the wall method with west system and then use some silicate filler for the fillets.
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No internal fillets or foam? I'd look into that to prevent the flutter from ripping the fins apart.
 
SinfulDarkLord said:
No internal fillets or foam? I'd look into that to prevent the flutter from ripping the fins apart.
Click to expand...

You think 3/16 carbon fiber and fiberglass composite fins would break? I had thought it would be thick enough to survive flutter
 
Last edited:
Mainless said:
You think 3/16 carbon fiber and fiberglass composite fins would break? I had thought it would be thick enough to survive flutter
Click to expand...

Its not that it would break more like it can flutter and break away from the body tube if not attached properly.
 
Mainless said:
So i should so some internal fillets for the fins?
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I think you could get a stronger and lighter overall structure by not slotting the tube, surface-mounting the fins, and then doing one or two tip-to-tip-type reinforcements. I have flown 54mm rockets with surface mounted plywood fins to Mach 2 with one layer of tip to tip carbon. No swept fins though.

Jim
 
JimJarvis50 said:
I think you could get a stronger and lighter overall structure by not slotting the tube, surface-mounting the fins, and then doing one or two tip-to-tip-type reinforcements. I have flown 54mm rockets with surface mounted plywood fins to Mach 2 with one layer of tip to tip carbon. No swept fins though.

Jim
Click to expand...

I would think that if one used a slotted fin and did inner fillets, the fin bond would have much more strength than epoxy bonding only on the airframe.
 
Mainless said:
I would think that if one used a slotted fin and did inner fillets, the fin bond would have much more strength than epoxy bonding only on the airframe.
Click to expand...

I'm sure that not everyone will agree with me, but it is my opinion that on the type of rocket you are designing (a smaller air frame that is near minimum diameter), a stronger result is obtained using the tip to tip approach than the through the wall approach. If your air frame was cardboard, then I would go with the through the wall approach. However, you are using fiberglass, so you have a good strong base, and cutting slots in the fiberglass just weakens the structure.

With the tip to tip approach, you are not relying on bonding the fin to the air frame. Rather, you are using the fin fillet and the tip-to-tip material to join the fin to the air frame to make a single structure that is very strong.

I've built many fin cans like the one shown. I fly them pretty hard and I have yet to lose a fin (I can be coupler-challenged from time to time). They are obviously carbon, which helps, but fiberglass works too. This one is 3" with two layers of carbon over a fillet made with a 1" diameter dowel.

One strategy that you can employ is to start with a thinner fin and then built up the thickness to what you want using the tip to tip material. That saves some weight and likely gives you an end product that is lighter than the corresponding through the wall approach (no fin tabs and one less set of fillets). The tip-to-tip approach is a bit harder to build, but the process is documented in many places.

Jim

Fin Can.jpg
 
Im using a carbon fiber airframe, and i was planning to have the tabs extra long in the front going up the rocket by about 1 1/2 inches, so any fluttering would pull on the airframe and not the fillets as much.
 
Mainless, when I first started doing rocketry I resolved to learn from those who have done it all before. Given what Jim has accomplished, if he's suggesting it you might want to consider it (or at least do some more research).
 
I'll have to agree with Jim, besides if the airframe is carbon then a surface mount would be most prefered.
 
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Mainless said:
Ill have to research how to do that I guess.
Click to expand...

Both methods will work and you can choose based on the tradeoffs. I just wanted you to be aware that you have alternatives that might make better use of the materials that you bought. Speaking of which, with a carbon tube, you also have the option just to surface mount with a fillet and no tip to tip. The rocket shown is 54mm with 1/8" fins. I flown it several times now to around Mach 2 (and the fillets are a bit better than the picture suggests).

Jim

IMG_0512.jpg
 
Yep, Mr. Jarvis is one of the most experienced CF builders around, I'd listen to him.
 

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