Skewer Construction

Plugging the tube ends

I used bottle necks that were shrunk down over a custom form to plug the ends of the tubes. I made the form on a friend's lathe, turned from a table leg. The wide part is 1.59 inches in diameter, the narrow part is 0.85 inches. The idea is to cut the bottom from a smallish bottle (16 or 20 oz.), place the top part over the form (with the narrow part of the form in the neck of the bottle), then shrink the bottle down with a heat gun. After trimming, you have a bottle neck that fits closely inside the tube and can be glued in place. You can see a finished rocket nozzle on the right.

One lesson I learned: if you smear the glue on the outside of the nozzle and the inside of the tube, then slide it in, the nozzle scrapes most of the glue off in the way in, and it's easy to create small voids in the glue joint. A better technique is to first slide the nozzle several inches up inside the tube, then smear glue on the inside of the tube and slowly pull the nozzle back out into position. This ensures a nice filled glue joint all around the nozzle. The joint is finished with the usual strapping tape to make sure the glue joint won't peel under pressure.

On the nose, I sank the bottle neck down inside the tube about an inch, so there was room for the nose cone to slip over it and its cap. The rocket was fueled with water from the top after it was on the pad, a cap was screwed on, then the nose was slipped over and taped on.

Internal Bulkhead

I also added a bulkhead about three feet up from the nozzle, just above the filled water level, to help support the rocket while it was on the pad, and to help it get started straight at launch. The launch tube was almost four feet long, so it went through both the nozzle and the bulkhead, extending above the bulkhead about a foot. The picture is terrible, but I also cut slots in the shoulder of the bulkhead to let the water flow through as the rocket was being filled.

Another lesson: I didn't account for the considerable volume that was displaced by the launch tube, so when the rocket was filled on the pad, the water level ended up a couple inches above the bulkhead. Probably no great loss in efficiency due to the slots in the bulkhead, but something to keep in mind.

I didn't want a glue smear all the way up to the bulkhead, so I took a piece of 1" PVC, squirted a glob of glue in one end, then inserted the PVC up into the rocket tube to about an inch below the location I wanted the bulkhead to end up. I used a long 3/4" dowel to push most of the glue out of the end of the PVC into the main tube, sort of like a crude syringe arrangement. A little clumsy smearing about with the dowel, then I pulled the dowel back into the PVC and slid the whole thing out. Then I took the pre-slotted bottle neck, mounted it on the end of a piece of 1/2" PVC that was wrapped with tape an inch from the end, and pushed it up inside the tube. It met the glue, then I pushed and twisted it for another inch or so until it reached it's final position, with a nice uniform glue joint all around. Still a bit messy, but not as bad as it could have been.

After the bulkhead was glued in, I glued in the neck, and while the glue was still wet on both I inserted a long rigid dowel that fit closely through the necks, to keep them aligned while the glue cured.

Fins

I used three small clipped delta fins, made from balsa wood and covered with Monokote. (Actually, this is the same fin unit I used earlier on the long-tailed rockets.) The balsa was shaped into a symmetrical airfoil: rounded leading edge, tapering to a knife edge at the rear. The fins were glued (using Shoe Goo) to a sleeve made from a length of the rocket tube, with a slit up one side. The fin unit was taped onto the rocket before launch.

Nose cone

The nose cone was a commercially available plastic one made by Estes to fit size "BT-60" body tubes. It's almost a perfect fit on these flourescent tubes, just a skootch too narrow, but close enough for me.

I guess that's about it. Feel free to write with any questions.

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