Largest blackpowder rocket I've built to date. Case of folder cardboard pasted with PVA, overwrapped with a sheet of pasted 80 gsm A4 to hold it together while drying. 12 mm ID, 20 mm OD, 105 mm long.
Used my newly treated cat litter clay for the 15 mm long nozzle and 6 mm bulkhead, now with added 5% wax for robust shiny nozzles. A 3 mm passfire hole drilled in the side of clay bulkhead. The 4 mm core went to within 20 mm of the bulkhead
The payload was contained in a pasted nosing extending 40 mm beyond tube. A teaspoon of pulverone as a break charge, some Granite stars, a small amount of paper wadding and a triangle fold to close the top.
Fused with a long length of Zn 'effects' blackmatch glued in place with some meal-NC paste. The propellant was my modified blackpowder rocket meal.
Large bamboo stick for stabilisation, hot-melt glued to motor casing.
Very Spectacular CATO!
Pieces of the propellant grain and head effects went 50 or more metres into the air. Enormous report that echoed off the cliffs.
Rocket actually left the launch tube and was blasted back into the sand a few feet away, stick first, it was found standing up at pretty much the same angle it was launched at.
The video isn't all that useful in determining the cause of the failure, frame-by-framing it you can see the motor just starting to develop thrust and leaving the launch pipe, then in the next frame a huge plume of fire is coming out the top.
The bulkhead was completely missing from the recovered motor, the nozzle was intact and burning on the stick shows some thrust was generated before the explosion (and it left the tube). The payload shroud was shredded and most of the stars were actually blown blind.
The altitude the propellant fragments reached was determined by comparison with the height of a nearby building from a report by a observer at a higher location. It was quite a spectacular mine, but unfortunately that was not the intention!
The cause of the motor failure is almost sure to have been the bulkhead giving way. The bulkhead was too thin to withstand the pressure this motor generated. A pre-ignition of the header effects seems very unlikely. A similar failure of a smaller device later that evening demonstrating the need for more robust bulkheads.
| title | type | size |
|---|---|---|
| Rocket CATO | video/x-msvideo | 840.650 kbytes |
| Pre-Test Picture | image/jpeg | 34.883 kbytes |
| Post-Mortem Picture #1 | image/jpeg | 27.508 kbytes |
| Post-Mortem Picture #2 | image/jpeg | 34.094 kbytes |