Beach Shoot #22 - Expedient Bottle Rocket Experiments
Date: 2004-02-08
Description
In an attempt to reduce the labour and time taken to make small 'novelty' scale rockets these simple devices were built as experiments in optimisation of the construction process.
Both devices were dry rolled from calculator tape paper, 50 mm wide. A total for 5 turns was made, the last turn pasted with PVA. The nozzle of one device was formed by choking the case with a piece of string, the other was crimped closed.
The propellant in each was 6:1:1 BP, ball milled for only 20 minutes. The propellant was funnel and wire loaded in three increments, with hand pressing of each increment.
The top of the rocket was sealed with some hot-melt glue.
A 2 mm OD metal BBQ skewer was pressed up through the nozzle to form the core in the weakly pressed grain. The core length was 20 mm in the crimped device and 35 mm in the choked one.
Both were fused with a piece of thin blackmatch, no priming.
A bamboo kebab stick was glued to the motor with a streak of hot-melt glue. Each device took a little under 3 minutes to make from scratch.
Comments
One CATO, one good flight.
The choked device was tested first, it exploded with a sharp report. The case was shreaded from just above the choke to where the hot-melt glue stopped, basically the entire length of the grain. The hot-melt plug was blown out completely taking a fragment of the case with it, the innermost layer of casing. As the casing was dry rolled this kind of failure was not unexpected, and in fact a much eariler device failed in exactly the same way, but its propellant was much faster burning.
The crimped nozzle rocket worked great. Its shorter core likely placed less stresses on the weak casing, but also limited its performance.
A stronger case should be made in future, either more turns, stronger paper, or wet rolled. I'd like to avoid wet rolling as it means the casing must be dried well before charging and is harder to make. I'd also like to keep its mass down. With a suitable metal case former (rather than a 5 mm OD timber dowel) wet rolling would be more practical.
The propellant seems good enough, as is the nozzle formed only from the casing material. The stick could be lighter and slightly longer in future, a similar kebab stick split down the middle would be close, but I'll try and find a more suitable stick as a ready-to-go commercial item.
Attachments
| title | type | size |
|---|---|---|
| Test Video (Choked Motor) | video/x-msvideo | 367.278 kbytes |
| Test Video (Crimped Motor) | video/x-msvideo | 664.300 kbytes |
| Pre-Test Picture | image/jpeg | 35.625 kbytes |
| Post-Mortem Picture (Choked Motor) | image/jpeg | 47.498 kbytes |