11 replies to this topic

[pritch]

Ok people, here are the specifications. Its a 5 cm paper tube with an id of 12 mm. Od is 18 mm.

I have spent all day grinding the meal using a heavy wooden handle in a hard plastic tub. I also may have added too much charcoal because someone told me to do so when I told them it was bubbling yellow. I now think the problem was that I hadn't ground it enough at that time so little lumps of sulphur were igniting. For my fuse I lack any dextrin or starch today so I couldn't make black match. Instead I poured some kno3 into an egg tub of water. I then soaked some newspaper in this mix. I tested it and it seems to burn well. I stuffed this into the end of my rocket which I have rammed to about 150% -200% of capacity if it was not rammed and then I poured all purpose filla around it to keep it in place. It's busy drying.

I am going to attach a paper nose cone and will wrap round some masking tape to attach that and the 12 inch dowel.

So come on what do you think will happen?

[PanMaster]

All purpose filler is what I have used for three test rocket engines I made a fortnight ago. Maybe I'll test one and see what happens, they look like giant bangers to me. I think the filler which is at least 20mm thick will hold but I doubt the tube will take the pressure of almost meal like powder. Theres no way I would ignite them outside. RocketTest

Edited by PanMaster, 24 April 2004 - 04:30 PM.

[pritch]

well my problem is my nozzle. Its basically the touche paper so once that burns I will have a nozzle roughly the size of my id.

So my case is defintely not going to explode. Worst case scenario is my rocket goes no where and I get an upside down fountain.

[Stuart]

I would recommend against putting a nose cone on now encase it does go out of control and hit someone. This would do more damage than if it was just the tube with nothing on the end

[pritch]

Ive just tested. I decided to do a static test in the ground because I was worried it would be a flaming ball and set a tree on fire or something.

Anyway. It burned for about 3-4 seconds and was a bit quite for my liking. It sounded like a gas burner. Like I could here some power there, like the sound wind makes when something flaps. THe flame was around 7 inches maybe and made a fair bit of smoke and sparks.


So what do you all think? I think I probally had too much charcoal which made it burn along time. How do you think it would have faired by the sounds of things?

[pritch]

Today im gonna use the same model but i've added a little more kno3 today. I think im gonna set it up on a scale or possibly a car now that I know it's safe. Im hoping to decrease burn time by about 1-2 seconds by increasing surface area and oxidizer. I think when I ram my last load im going to try to form like a cone shape instead of a flat surface. Plus today for my nozzle im going to super glue a metal washer to the bottom. Thanks to steve the admin for that idea.

[alany]

Ewww, god don't do that! It is totally unnecessary.

Just ram some clay or cat litter about 10-15 mm thick for the nozzle, ram your propellant almost to the top and then close with more clay or some hot-melt glue. Cautiously drill out the nozzle, a 4-5 mm drill should be a good starting point.

The depth of the core is the main tuning parameter, start with 15-25 mm into the grain, it depends on the speed of your propellant, if if blows up shorten it, if the thrust is low increase it. Try 6:3:1 BP and a long core, or 6:1:1 and a short or no core.

[pritch]

when you say 6:3:1 bp do you mean 6 parts kno3, 3 parts charcoal, 1 part sulphur?

Also im having a bit of a mishap with the fuse. The shops are closed today so I can't get any cornflour or kitty litter. So I have no dextrin and only all purpose filler or that washer technique. Im waiting on some touche paper to dry and i've also tried putting cotton string in the solution. I think I might just use the filler again cause I have a feeling the touche paper wont burn through the washer which has an id that fits your average screw. Yesterday when I made it i never really stirred the water up much plus im using toilet paper today, thanks again to steve so hopefully I will weild better results.

[alany]

when you say 6:3:1 bp do you mean 6 parts kno3, 3 parts charcoal, 1 part sulphur?

Yep.

Also im having a bit of a mishap with the fuse. The shops are closed today so I can't get any cornflour or kitty litter. So I have no dextrin and only all purpose filler or that washer technique. Im waiting on some touche paper to dry and i've also tried putting cotton string in the solution. I think I might just use the filler again cause I have a feeling the touche paper wont burn through the washer which has an id that fits your average screw. Yesterday when I made it i never really stirred the water up much plus im using toilet paper today, thanks again to steve so hopefully I will weild better results.

Blackmatch is far better than touchpaper, especially for burning through narrow holes.

Your next best bet is to make chinese cracker fuse, if you have tissue paper or even kitchen paper try cutting a piece about 20 mm wide and 100 mm or so long. Fold it down the middle to give a Vee shaped trough, run a trail of your BP down the middle (not too thin, it is better to use too much than too little) then pick it up, close the fold and start twisting it from one end. Once twisted up, roll it against the table and your hand (or a flat board with a handle, a book, anything holdable with a flat surface etc) to tighten it. It takes a bit of practice, and there are better but more fiddly methods, like the ones the chinese actually use with dampened gampi tissue, but you can make a servicable fuse with a dry process and some care.

Test a piece first, it has a nasty habit of quick-matching all the way through if not twisted tight enough. Doing the same thing with a meal/NC lacquer slurry makes an excellent fuse, even meal/water works, but takes longer to dry.

[pritch]

Thanks that chinese cracker fuse sounds interesting. I'm not going to be making anything else till I have all the proper gear though. I will be making a mill and buying everything else a pyro should have this week. Also though that touche paper I made out of tissue paper seems to have worked very well. That touche cotton string however failed miserably. Strangely it wouldn't even burn with a flame. Just smoldered painfully slow, in fact dangerously slow and gave the odd spark.

Oh and I could not be bothered to spend hours making more poor quality bp, so I just used what was left over from yesterday. There was probally only 3 grams out of a 10 gram batch left. I must have packed yesterdays rocket real good. Anyway it was a no go. I also made an e-fuse with a 15 -20 foot power cable. That wouldn't fit the nozzle and was just an experiment.

[Phoenix]

You can use touchpaper as a fuse for things with a choke. What you need to do is cut a stip of touchpaper that is long enough to wrap around the outside of your tube at least once, and wide enough that you can twist the end together once it is wrapped around (like a nosing paper), with a couple of centimetres spare to light and about 1cm to glue to the tube. Apply a bit of glue to the bottom 1cm, wrap it around, then fill the core of the rocket with BP. Grain BP is much better for rockets, as the whole of the core lights instantly, but you can probably get away with meal or green mix, if you are careful to keep it fluffy. Once the core is full, put a little on top of the nozzle, and twist the touchpaper closed on top of it.

There is a danger that some of the BP priming can get into the touchpaper and flash straight to the motor, so this method is not really suited to anything larger than a bottle rocket, but the risk of this happening can be reduced somewhat by trying to keep the lighting end of the touchpaper open, whilst twisting it tightly at the bottom (nearest the nozzle). If the lighting end is more open, it is less likely to have BP trapped in it.

Well made cracker fuse is certainly better than this, but as alany said, dry rolled craker fuse has a habit of flashing through. This can be reduced somewhat by dampening it (preferably with dextrin solution or thin wallpaper paste) after it has been rolled, then giving it another twist, and placing weights on the ends to stop it untwisting whilst it dries. Incidentally, black match can be made with wallpaper paste as well as dextrin. Use less wallpaper paste (2.5%) or you will get BP gel rather than slurry. In fact well diluted PVA might even work, but I haven't tried that.

Finally, the nozzle. You could try slightly dampening your all purpose filler, then ramming and drilling it. Failing that you could roll a case and crimp it, but you'd have to wait until tomorrow for it to dry, by which time you could just buy some cat litter anyway

Edited by Phoenix, 25 April 2004 - 04:57 PM.

[alany]

I've had a bottle rocket explode from having -40 mesh priming up its core. In hind-sight it is likely why a few of my choked motors have exploded too, stray granules of BP inside the motor that over-pressured the case.

I guess that is the risk I run using 6:1:1, 15:3:2 and similar hot propellants in rockets to get high performance, any kind of grain defect and I have a salute on a stick.