Dean Roth's Tech Tips #1

Rocket Repair 101

My oldest surviving high power rocket, built in '96, had a rough landing on Sunday, October 8, on Bong's gravel runway. A chip was knocked out of a fin, and at least one fillet was broken away from the plywood fin. It had an even rougher landing on Wednesday, October 18, when the parachute failed to exit the deployment bag due to poor preparation work. The rocket landed with only a 23" pilot chute to slow it's descent.

Damage included a crumpled bottom of the upper section. It has a couple layers of 2 ounce fiberglass cloth. I cut 1" off the bottom and it looks fine. Without the fiberglass laminate the damage would have been much worse. Landing in the grass would have resulted in little damage.

The fin can lost a fin. The same fin that was damaged on Oct 8 broke free. The fin was not damaged. It was just no longer attached to the rocket.

My first thought was to trash the fin canister. Then I figured that I had nothing to lose, so I tried using two-part, expanding urethane foam to attach the fin. The foam is very sticky and turns into a solid.

I cut two access holes on each side of the fin to pour the liquid that would foam into the space between the motor mount tube and airframe. I inserted the fin, mixed the foam and poured it in. Two applications were used on each side of the fin to avoid over filling the space. (It's hard to predict how much the foam will expand. Expansion is dependent on temperature.) The fin seems as firmly attached, or more firmly attached, as when it was epoxied in place.

I plan to fly the rocket next Wednesday.

Dean