Corkscrew Build Part 5 Kevlar and Elastic Shock Cord Tying

Tying the elastic end of the shock cord below the top of the tube will prevent zippers.

For any "new-be":

A Zipper is when the Kevlar cuts a jagged line down through the top of the tube. This usually happens when the rocket is traveling too fast at ejection. The Kevlar can snap back cutting a jagged line right through a few inches of the upper tube.

If the Kevlar is beneath the top of the tube you can eliminate any chance of a zipper. The elastic shock cord won't cut through the tube.

Here's how to tie the Kevlar to the elastic BELOW the top:

With the Kevlar fed through the front of the tube, mark it just below the top lip of the tube.

You are going to tie on the elastic below that mark you just made.

Feed the Kevlar back through the back end. Long tweezers or a notched dowel can come in handy here.

Tie the elastic to the Kevlar while it is extended out the back, engine end of the rocket. You won't be able to tie the knot inside the rocket from the top. You'll have to do this from the back end.

You can see the mark I made on the Kevlar on the right side of the picture. The right side of the Kevlar is the loose end side. The rocket body is to the left.

I started the knot away from the mark to insure the knot will be inside the body.

This time a square knot was tied to join the two cords.

Apply a small drop of glue and trim off the excess ends.

Feed the elastic back through to the front end of the tube and you are good to go!

Both the Kevlar and knot are below the top of the tube end.