Internal Fiberglassing

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A

Austin

Internal Fiberglassing: Adding strength to any high power rocket is always a plus, so I used the following technique to strengthen the area where the fins are glued to the motor mount tube. It is MUCH stronger than fillets, even though you still can add fillets after you apply this method. Glue your fins to the body tube following the manufacturer's directions. Cut some fiberglass cloth strips to the length of each fin and wide enough so it will lay across the motor mount tube about one inch, then up the inside fin and across the inside of the body tube about one inch. Mix some 15 minute epoxy and soak the cloth. Using a 1/2 wide stick, wrap the soaked cloth around the stick and insert the cloth into the area. The sitck is used to press the cloth down on all surfaces. Finally, Clean up any excess resin with denatured alcohol and repeat for the remaining fins. You will have a joint that is VERY strong, which is my first rule-of-thumb for High Power rocketry.
 
A similar technique that I use for putting larger MMTs in modrocs is how I strengthened the joints in a Big Daddy that I converted to a G-55. The Big Dady is a through the tube fin mount

Make an extra centering ring. Place it near the top and another about 1/3 below, but make sure that you do not place it below where the top of the fin tab will line up. Glue in place. Slide the MMT into the rocket...but do not attach the bottom centering ring! Attach the fins per the instructions. Then pour fillets inside on all the joints: fin to body tube, external fin joint and inside body tube wall. I use a small plastic baster that is cleaned

After it all sets place the bottom centering ring in. Makes an incedably strong joint. To make a smooth fin I use label paper that I then coat with thin CA.

Never had a problem!
 
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