There are several options to consider when repairing a zipper. If the zipper is short and the rocket design allows for it, cutting off the end of the tube with the zipper is often the easiest way to proceed. Here is a 4” Sandhawk that sustained some minor damage to the end of the body tube after being dragged through rocks. Since there was no reason this part could not be removed, cutting it off was the simplest solution. A hose clamp was used to obtain a straight cut. John Coker has an excellent article in the CONSTRUCTION area on making a cutting jig, but it can be hard to put a rocket with fins and launch lugs into the jig. This body tube had been fiberglassed, so there was no problem tightening the clamp. After several passes with the Exacto blade, the end was removed, lightly sanded, and ready to fly.

However, four inches of this Iris could not be cut off without ruining the scale appearance. This rocket also has two small holes drilled for shear pins that would have to be redone. Therefore, repairing the section makes the most sense. Here is the problem to the left. The body tube is 7.5” fiberglassed Giant Leap tubing. The problem area was cut out with a Dremel tool and the remaining area sanded to remove the paint to ensure adequate bonding.

An 18” section of body tubing left over from construction of the rocket served as the donor for a replacement section. The cut out zipper section was placed on the good tube, an outlines was drawn, and the new section cut out. After some sanding, you can see how the section fits in (left).

A section of 5.6 ounce carbon fiber cloth was cut out to use, although appropriate S-glass can be used also. Masking tape was placed on the inside seams to keep the replacement piece in place and to prevent epoxy from running inside the tube. An extra bulkhead was also placed inside to keep the piece in place. West System epoxy was used (105 resin and 206 hardener). The area to be bonded was wetted, and a small amount poured off and mixed with 406 filler. This thickened epoxy was filled into the seams to make them flush. The carbon fiber cloth was then placed on the body tube in the correct position and wetted with unthickened epoxy. A layer of Teflon-coated release film was placed over the cloth (as seen to the right). Then a layer of breather fabric was placed over this, and masking tape was wrapped around the tube to apply pressure to remove excess epoxy. Most people do not have a system large enough to vacuum bag tubing this large, though heat-shrink tape could be used to apply pressure.

After a partial cure (about 8 hours), the sanded area was expanded and a larger piece of 3.6 ounce S-glass was applied over the carbon fiber in the same manner. The excess was cut off from the end of the tube and everything was allowed to cure. There was enough room inside the tube to put a layer of 3.6 ounce S-glass on the inside of the repair section and still get the body sections together. The inside area was wetted out, and the seams again filled flush with some thickened epoxy. The fiberglass was placed inside and wetted. Then a layer of Teflon-coated release film was placed over the cloth, followed by breather fabric. Masking tape was not a good option to apply pressure on the inside of the body tube, so the ‘old balloon trick’ was used as seen to the left. This can also be used to fiberglass the inside of couplers.

Submitted by: Dale Emery