Fin Support/Attachment

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Manwithbeers

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For High Power Builders

I have a problem with a PVC airframe with surface mount fins.
The fins are glued onto the airframe with CA and then fiberglassed in place with 4 inch wide 6 oz. tape. The airframe is 4". The problem happened while travelling in a car. A fin was bent over and the CA joint under the fiberglass was cracked so I had to drill through the fiberglass to re glue it. I decided to go with my original plan to mount support braces of aluminum.

The rocket is NOT intended to reach MACH speeds. It is actually only a booster section.

I've already done the forward root end of each of the 4 fins. I was going to put 3 strips on each fin. As I was installing the forward braces I thought all the holes in the PCV is weakening it so I want to limit the holes now.

I'll post two pictures. The first with a 2 brace per fin view and the second with a 3 brace per fin view. The screws are 3mm x 8 mm SS with nut on other side as you can see on the fin pictures. 6 screws per brace. Each brace is 9 cm long (~3.5 in?), 1 cm wide.

I'd like your opinion. Which will be better?

This photo 2 braces shown.
 

Missileman

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I vote for 2 sets of braces with the aft set on the opposite side of the fin to help offset any spin caused by the braces being on one side.
 

Zippy

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I'd brace along the entire length of all fins, both sides. Not becouse it needs it (way overkill) but becouse it looks cool and scale like.
 

Manwithbeers

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Well,

I'm going with the most popular selection. After taking a couple days to think it over it's my favorite option too.

2 braces per fin.

Thanks to the voters!
 

Ryan S.

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interesting, is there any way you can put 4 on each fin? To make is symmetrical?

btw can we hear more about the rocket and see some more pics? :p
 

daveyfire

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COOL! Reminds me of Scott Bartel's Optimal kits a while back... never did see a fin come off of one of those ;)

How big/what motor?
 

Manwithbeers

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Originally posted by Ryan S.
interesting, is there any way you can put 4 on each fin? To make is symmetrical?

btw can we hear more about the rocket and see some more pics? :p
I could put braces on each side but the thing is on a diet so it can be launched on a J295 again.

As noted above the rocket has a PVC airframe. Light sewer pipe. It's 8 feet 8 inches tall when assembled as a 2-Stage rocket and it's meant to fly on Pro54 J295 or K445 in the booster and a Pro38 I287 in the 2nd stage.

The booster section can also replace the sustainer fincan flying it as a single stage rocket with either fincan.

The sustainer fincan has a 38mm motor mount. The motor tube is a piece of fiberglass tube I made and It has TTW fins attached to that motor tube. I've flown it on an I287 to about 1000 feet.

The Booster/sustainer fin can Has larger surface mounted fins and an exchangeable motor retention system that curently has an aluminum thrust ring and plywood centering rings for a 54mm mount but It would be very easy to make new rings and thrust plates for 75mm or even 38mm.

Rocksim file attached.
 

Manwithbeers

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The rest of the airframe includes sections for the lower payload (36" drogue) the electronics bay (Perfecflite MAWD and MT2) and the upper payload (60" hemisphere chute). I built the nosecone myself. It has a expanded polystyrene core with a couple layers of glass and lots of West Systems with lightweight filler.

It's never had a chance to do a 2 stage flight. Both fin cans were flown and the highest flight so far was 3409 feet on the CTI Pro54 J295

Flying again with the Calgary, AB Rocket Club on Sept 17th at the LDRS 24 launch site.
 
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