Papering already installed fins

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gna

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One of my favorite rockets is the Semroc Vega, which I have flown more than any other rocket. I have managed to break every fin, some more than once, in the same spot:
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Is it possible to paper an already installed fin? I'm thinking of sanding off the paint, and gluing paper reinforcements on the sides of the fins, sealing, then repainting. Or is it not worth the hassle?
 

K'Tesh

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You might opt for 1/64" ply instead of paper.
 

neil_w

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If you paper them, max strength will be gotten either from 1/64" ply as K'Tesh suggests, or cardstock rather than just plain old paper. Either will add weight, but I suspect not a problem in a Vega.

However, I think that removing those fins and replacing them with papered fins would be easier and better. You wouldn't need to spend time sanding off the existing paint, and also you'd be starting fresh with nice strong fins instead of trying to salvage the ones that already have that clean break through them. If you don't want to remove them all the way at the root, you can cut off the existing fins just above the root, leaving a sliver of clean balsa to attach the new ones. Just a thought.

This is why (almost) none of my scratch designs have fins swept way past the back of the airframe like that. :)
 
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Back_at_it

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Can it be done? Yes. Is it worth the effort, that is up to you. I had an Estes Skyhook that would break the fins right at the bend almost every flight. After breaking all three fins I sanded off the paint and used note cards to paper them. The process wasn't too bad but I wouldn't do it again if I had a choice.

Basically I had to lay each fin on a flat surface and sand until I was down to 90% bare wood. Keep in mind that you need to get the paint off the area where the fin attached to the body as well. I then applied a super light film of Elmers white glue to the fins and added the card stock. The hard part was supporting the rocket body and figuring out how to clamp the papered fin between two large flat objects while everything dried. For the Sky Hook I repeated this three times. From there I added fillets and filled and sanded the fin edges.

If it were me I would cut off the existing fins off, make patterns and cut new fins out of Basswood and call it a day. I really dislike papering fins but I might give it another shot with an upcoming 24mm Bertha build I have planned.
 

BABAR

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Outside the box option.
After fixing your fins, mount a kevlar loop that is accessible from the BOTTOM of the rocket, big enough to hook onto with a strong snap swivel, small enough to tuck out of the way for display. When you launch, hook your shock cord line up with a snap swivel, run your cord up the launch lug side so spectators dont see it. Rocket body will come down nose end first. You may want to reinforce the front end of the body with CA.

Another option is to attach the loop to the balance point on the body of the rocket (balance point excluding chute and including expended casing.) Rocket descends horizontally.
 

gldknght

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Outside the box option.
After fixing your fins, mount a kevlar loop that is accessible from the BOTTOM of the rocket, big enough to hook onto with a strong snap swivel, small enough to tuck out of the way for display. When you launch, hook your shock cord line up with a snap swivel, run your cord up the launch lug side so spectators dont see it. Rocket body will come down nose end first. You may want to reinforce the front end of the body with CA.

Another option is to attach the loop to the balance point on the body of the rocket (balance point excluding chute and including expended casing.) Rocket descends horizontally.
An interesting idea. How do you then get the shock cord inside the body tube without binding up the nose cone, or where ever the separation point is?
 

K'Tesh

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An interesting idea. How do you then get the shock cord inside the body tube without binding up the nose cone, or where ever the separation point is?
It's not the rubber shock cord line that is external to the rocket, just a length of the same kind of string that is used for parachutes that is tied to the swivel. The rubber shock cord is contained inside the rocket, until the ejection event. It's quite similar to the system used for some competition rockets, or the old Centuri optional method of recovering the Mercury Redstone nosecone without destroying the tower. A change I'd recommend based on the image (below) is that I'd attach a rubber (or elastic) shock cord at the junction between the string (at the 12"/8" location) and the parachute.

 
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BABAR

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I use Kevlar thread for most shock cords, sometimes with a section of elastic. The thread is strong enough for my low power rockets, and the section that goes between the cone and the rocket body doesn't cause me any significant resistance to cone deployment.

As K'Tesh suggests, if I used elastic that section IS stuffed inside the tube.

I am guessing a similar technique is used for duration competition models to get body to fall horizontal.

YAMV (your altitude may vary)
 
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