Building my Cherry Coke rocket

I'd been looking at the 20 ounce plastic Coke bottles at work and thinking, "I can make that into a rocket!" I decided to try building a rocket for Sarah, who collects Coke bottles and memorabilia.

The first step was to design fins. I read on rec.models.rockets about someone who had made a Coke bottle rocket, but complained that it didn't fly straight. Another reader replied that it would have been more stable if he included fins! I decided to make long sweeping fins like the old 1930's view of a rocket. The longest dimension was 16.5 cm. I included a "tab" to project through slots in the wall of the bottle:

I traced this onto the paper covering a 1/8" (~2 mm) sheet of plexiglass, and cut out each fin using a coping saw. I prepared five, since the Coke bottle has five sections.

In order to achieve the illusion that a "full" Coke bottle was flying, I painted the inside of an empty bottle with brown Testers enamel paint by pouring the whole bottle in through the neck then slowly turning the bottle to swirl the paint around.. After it dried, I cut slits in the side of the body using an Exacto knife, then glued the fins using an electric hot glue gun (above left).

Next, I needed a hole in the bottom of the Coke bottle. I tried several means, then settled on using a 1 inch drill bit. The drill bit came with a door knob kit.

I carefully drilled through the center of the bottom, then inserted a length of BT-20 Estes body tube, with an engine hook to hold the engine at the back end. On the front end, I glued (carpenter's glue) a retaining ring (BT-50 size?), then glued (carpenter's glue again) the completed assembly so that the retaining ring was wedged just inside the neck of the bottle and the engine mount extends outside the body approximately one-quarter inch.

I used an ~1/8" drill bit to make two small holes in the base of the screw neck (behind the bottom part of the screw cap which stays behind), tied a loop of string through the holes, and connected a conventional shock cord and parachute to that string. For a nose cone, I took the cap from the Cherry Coke, and shaved off the internal threads using an Exacto knife. This permitted the "nose cone" to pop off with the engine ejection charge. I prepared a small loop from copper wire (a paperclip would have worked as well), then glued it to the inside of the cap using hot glue. I tied this cap to the shock cord with thread. The finishing touch was a plastic drinking straw (white with a red stripe), which I glued onto the outside of the bottle using small drops of hot glue to connect it at two points (the straw is attached below the fin at the 3 o'clock position in the following picture).

Here's the completed rocket viewed from the bottom as I inserted the engine (the yellow plug in the center holds the ingition wires in the engine prior to launch, and the horizontal red tape keeps the ignition wires from shorting):

and here's the finished rocket on the pad:

STATUS: Our first launch was with an A8-3 engine, because I had no way to predict how high it might fly. The first flight only went ~20 feet into the air, and the parachute opened ~5 feet above ground. It was enough to slow the descent. Next we tried a more powerful engine, and I measured the altitude. The rocket flew ~330 feet on a C5-3 engine! One of the fins detached from the body, so I scraped the old hot glue off the fin with an Exacto knife and reconnected it with hot glue (see above).

Here it is in flight with a C5-3 engine. Estimated altitude was ~110 meters (~340 feet)!!! The chute opened successfully, and it glided down to a semi-gentle landing. Another fin came loose, so we didn't try launching it again. The fins have been reglued, and it's ready for another flight!