Photocopier paper (80 gsm) case, 15 layers taped, no glue. 6 mm ID, 50 mm overall length. 2 mm diameter cavity full length of the 40 mm long grain. Cat litter nozzle, 8 mm thick. Bulkhead of paper wadding and hot-melt glue.
Standard ballmilled blackpowder meal propellant (75/15/10).
Core was formed by ramming over a mandrel.
Fused with meal-NC tissue paper fuse, no priming.
Standard bamboo kebab stick stabilizer, not painted as I didn't expect to recover the rocket if it worked well. It was however labeled seperately from the motor (as always) in case of a CATO seperating the stick from the motor.
Pretty average CATO.
It is becoming apparent that these flimsy cases combined with my rather hot BP meal is pretty much always going to end up in a CATO. I'll try one more batch, with PVA-glued cases, if they fail I'll have to consider cooling down the propellant.
They would probably function perfectly with greenmix or 'half-hour' meal as they have with the KN/Sucrose/IO (pinkmix?) propellant. I am curious if 'Rcandy' would over-pressure the case.
This rocket was recovered the following day. I was able to observe the burning remains falling back to earth. In the morning a quick search of the general are with binoculars located the remains of rocket caught in a small shrub on the edge of the cliff.
The case was blown open just above where the stick ended. I am unsure if that is significant. Perhaps the extra layer of tape (attaching the stick) helped contain the lower half of the motor case?
The fracture was length-wise, classic hoop-stress failure? It does appear that the fracture propagation was stopped by the extra layer of tape holding the stick to the motor. I find it curious that two extra layers of tape could stop a zippering tear while 15 layers of paper and 2 of tape couldn't.
Maybe a crack develops in the grain as the pressure expands the case slightly. Maybe my meal is just too hot to be used with this core length, but I've had failures with much shorter cores as well?
The nozzle was undamaged. The stick burns showed signs of significant thrusting. From the sound on the video the motor did produce thrust for about 200 ms before exploding. The rocket did make about 50-100 metres down-range so it must have put out a bit of thrust.
Because the bulkhead only bonds to the inner-most layer of paper these taped cases will likely always suffer bulkhead failures, even if I add sufficient layers and tape to prevent hoop failures. The inner-most layers always burn through, allowing the bulkhead to slide like a piston. I need to stop being lazy and make fully pasted cases with my special corn starch glue or PVA.
I did not recover the bulkhead, as I picked up the rocket, the inner layers of paper (which were reduced to whitish ash from free-air burning) fell away, taking the bulkhead with them over the cliff. (Bugger!)
| title | type | size |
|---|---|---|
| Rocket CATO | video/x-msvideo | 1.076 Mbytes |
| Pre-Launch Picture | image/jpeg | 23.311 kbytes |
| Post-Mortem Picture | image/jpeg | 63.423 kbytes |
| Landing Zone Picture | image/jpeg | 69.184 kbytes |