21 replies to this topic

[pritch]

My second nozzle was made with a 4 mm drill bit. I made the core almost half the length of the propellant. Also I dry rammed it.Im thinking maybe my nozzle is causing problems. You see its basically at the very bottom of the case. So its a perfectly flat surface with the hole in the middle. I know the best way to do it, using a spindle is to have like a lip using the casing. So theres more of a pocket.

[willd]

I have made many successful rockets with no lip, but i use a smaller nozzle than that about 3mm for rockets of that size.

[chim-chim]

It lifted off. Maybe 1 foot. Then just burned away in its guider.

Im thinking. Maybe the stick is too heavy. Its just a piece of dowel.

Fireplace matches make for a cheap stick for small rockets, about a foot long and are quite light. Of course you'll want to trim the match heads off.

[alany]

The bamboo kebab stick is really the best for small motors IMO. The cost less than $1 AUD for hundreds. Can be split down the middle for really small motors. Come in a range of lengths, all weighing less than 1g or so. They are usually very straight too.

A nipple is by no means required to make a rocket, but it helps lock in the nozzle and bulkhead plugs. Core burners tend to blow the bulkhead more than the nozzle, at least that is my experence.

[pritch]

I made another. Exactly the same as the others apart from the nozzle size and ramming technique. I used a 3 mm nozzle this time and I used a vice to pack in the propellant. So I lit it. Expecting the fuse to not even make it through the tiny nozzle and whoosh!. It probally went up around 50 - 80 feet, with a nice sparkling tale.
Oh I also used a longer core. The core was over half the length of the rocket.
So im quite chuffed

My next idea is to use a much thinner paper case. Just thick enough to keep rigid while I ram. After I have rammed I am then going to add another layer around it, only further down to create a pocket at the nozzle.
I think if I use a decent nozzle, properly rammed because im using a hollow plastic rammer right now that bends under too much pressure and a nose cone then I should have my first decent quality rocket

[alany]

It doesn't need to be that high-tech. I wouldn't try thinner cases, they'll just split durring ramming.

Just a nice stout tube about 10 times its ID long, a nozzle about an 3/4-1 ID thick, a core about 7 ID deep from the bottom of the tube, a 1/3 ID nozzle hole and cavity, and another 3/4-1 ID plug at the top. The main problem should be stopping your rocket from exploding in core-burner configuration, not having thrust problems.

Try 6:3:1 greenmix, that just about always works, 6:1:1 is often too hot. Ball milled meal + 25% 60 mesh charcoal works well in larger devices. A half-ID nipple is pretty good, some use closer to an ID. For tooling you need nothing more than a mallet and a dowel if you are going to cautiously drill out the core, but I highly recommend well-made tooling if you want to make large batches of devices.

[pritch]

Just had another succesfull launch

This time I used a 15 mm id and about an 18 od. The case split when I was ramming so I fixed that up with plenty of tape
It was higher than last time and straighter but im still not happy. I hoped it would go twice as high as the last one due to having allot more propellant. One thing I didn't do is drill the core quite as deep. My meal is faster burning this time and with it being more compact I was scared of a cato.

Do you think 3mm is too small for the nozzle and core with a 15mm id?
Do you think it will make much difference if I can make a cavity for the nozzle?

I also never used a nose cone

ps im joining passfire right now


Ive just scaled down one of Richard Nakkas large rocket motors. My 15mm id with a 3 mm core is exactly 4 times smaller. So by a bit of luck it seems im working with a winning formula The only difference is that my motor is too short and my core is much smaller. He uses a 100 percent length core which is thicker than the nozzle.

Edited by pritch, 11 May 2004 - 12:07 AM.