60 replies to this topic

[alany]

- The rocket can then be fused as desired. So far I have used, and probably will continue to use a smear of priming into and over the nozzle, then a twist of touchpaper over this.

You must have read my mind, I made a couple of sheets of touchpaper last night. Didn't have any blue or pink die to make it authentic looking though. The nozzleless ones take fire very easily from a twisted nosing of touch paper.

Adding a delay on top of the composition would, as far as I can see, greatly increase construction time and fiddliness with little added benefit. Therefore a heading is put straight on top of the composition.

I can't see any point for extra delay either, just let the grain time the effects.

I'd like to get it working nozzleless, then I don't need clay. I've had some luck with them end-burning and a crimped casing nozzle, which is promising. Avoiding forming the core would save much time, but having to crimp the case in 4 or more places makes it a lot more like making crackers. The core burners are more sensitive to propellant type and so far 2 of 5 tests with the core burners have exploded (likely because I didn't press them well enough, but still not encouraging if I want to avoid ramming them with a mallet).

I guess using whistle propellant would solve a lot of problems. I read an old AFN article about end-burning nozzleless Magnesium bottle rockets. They used:

1 Potassium Nitrate
1 Magnesium (100 mesh)
1/8 Dextrin

And a lot of variations giving different colours. Unfortunately I have no suitable magnesium to give them a go, and substution with fine Al flake has not worked well - made an excellent falls torch though!

The moistened propellant ones have all worked well and can be pressed easily, but the drying time is pretty long. What about redgum and alcohol instead of dextrin and water? Would it get driven in, or have insufficient binding power? Would it actually help drying time at all? The go-getters used acetone and took forever to dry.

[Phoenix]

Well, I just tried my damp hand pressed charcoal rich rocket, and it took off, went about 2m, then blew up.

However, I made a couple with the same fuel, by the same method (hand pressing) but without dampening the fuel. They worked fine. I know that people are probably thinking that my fuel grain shrank on drying, and left a cavity around the side, but it wasn't damp like star comp. It was damp like BP about to be pressed. I don't think shrinking was the issue. I think it was the "sand in a tube" effect, and the damp comp experienced more friction with the tube walls than the dry comp did (it was certainly less fluid) so there were loose areas and cavities left in it. Both of the rockets that I pressed dry worked fine. Probably using smaller increments would solve this, but why bother? The dry mix is easier to sift into the tubes and I should be able to use bigger increments and so save time. I will try making a batch of rockets using this method at the weekend (since I still have about 50 choked cracker tubes left).

I also made a plaster choked rocket by assembling it as per my above post, then pushing in a nail to form the nozzle. Seemed to work OK. However, I used damp propellant, so I'll have my fingers in my ears when I test it.

[alany]

John Reilly just posted a good description of simple bottle rockets in rec.pyrotechnics. It is under the thread "mini rockets".

Oddly enough it is very similar to what we've been arriving at by trial and error, convergent engineering I guess?

I suspect it was the salt-bag effect that made my choked motors explode too. Last night I made a nice little adjustable powder scoup, much like the one Rich Wolter sells, but using a straw and a kebab skewer wrapped with tape. It let me consistantly ram a motor, complete with clay nozzle. It didn't perform to well, but it was end-burning. I am going to try again tonight with a few different core lengths to see if I can dial-in the design to match this propellant.

[alany]

Phoenix and Matt et al, I've got them basically working:

http://www.vk2zay.ne...vice.php?id=152

The videos suck, there isn't really a lot to see without an effects tail, but they accelerate like a bat out of hell and make at least 100 ft before swiming around like a fish for a second or two. Eventually I'll add a little flash for a report.

[BurlHorse]

Alan,

Great Link, Great documentation, I'd say you're perfecting them nicely!

Regards, Stay Green

Bear

[Phoenix]

Nice work Alan. This morning I made a batch of rocket propellant:

Potassium Nitrate...60
Charcoal (Blender).30
Sulphur..................10

The KNO3, S and 1/3 (10% - kind of - you know what I mean) of the C was ball milled to dust. The remainder of the charcoal was then added and milled for a few minutes. This stuff is quite cool - perhaps too cool for such small motors, but would cerainly work well in larger rockets. Nice tail.

I then spent much of today messing about with rockets, and I'm halfway through a batch of 1/4" motors made from the cracker cases.

I made the coring tool I described, and tried three plaster choked rockets. I couldn't quickly push it into the plaster and propellant grain as I'd hoped. I had to support the motor on the inside w/ a dowel, and then gently hammer it onto the spindle. Two rockets came out apparantly OK (they're drying) but one's choke cracked badly when I withdrew the spindle, so I unrolled the case and salvaged the propellant.

I found that with this propellant, the 1/4" clay choked motors would ascend very slowly if they were just primed at the nozzle. However, if I pushed an awl into the choke to give a 2cm long core, they really did go fast. I also made one like this, but filled the whole case with propellant (7cm) this shot up, and kept going, and kept going, and kept going, and kept going. I can't judge long distances, but after the propellant burnt out it took about 5 seconds to fall back down again.

So far I have stayed away from crimped motors, as I found them quite slow to make - more so than I thought my plaster ones would be. However, two developments have caused me to consider them. The first is that plaster chokes take longer to make than planned, and the second is that, after a flash of inspiration and some experimentation, I have found that newspaper tubes are really, really easy to crimp. Even dry rolled A4 was difficult to quickly crimp, but the newspaper tubes are much softer, and therefore much faster. I also like the look of crimped motors, so long as they're neat.

I have half filled the cracker cases with propellant, which has also filled the nozzles, so all I need to is twist touchpaper around them and fix em to sticks. As they are, the ascend a little slowly, but I don't really want to have to drill or hammer cores in them, so I'll just say "gracefully" not "slowly," and not bother with headings.

I think what I might do is make a block of 1.5cm long pins for the wet rolled newspaper tubes to sit on, and use shifting boards to fill them, since sieving propellant in was very messy and inconsistant. If I make this set right I could use it for small gerbs and candles as well. I can then fill my 1/4" tubes about half full with propellant (something hotter than this - I'll save it for bigger things) and then wet the empty bottom bit to soften them, and crimp and tie the bottoms around a spindle. I might make one of those hinged crimpy machines in Weingart's book to speed things up too. I'm hooked on bottle rockets at the moment...

[Matt]

I feel that i should be a part of this race...... Oh well. Anyways im making a 50 mortar 2 inch rack. 5 rows of 10, the 5 racks are run next to each other in a fanned fashion. Just 2 more rows to go!!

-Matt

[BurlHorse]

Phoenix, another good post, man these are getting great!

Not too sure what a 50 rack has to do with bottle or otherwise rockets though......

Fanned Mortars are always nice though....

Regards, Stay Green,

Bear

[Matt]

well.... uhhhh, im getting the uh rack ready.. for.... my 2 inch shells of serpents... which these lovely scientists can uhh look into and give us all tips for ease of construction... heh heh heh.

-Matt

[BurlHorse]

well.... uhhhh, im getting the uh rack ready.. for.... my 2 inch shells of serpents... which these lovely scientists can uhh look into and give us all tips for ease of construction... heh heh heh.

-Matt

Hmmmm scientist, don't think I'm qualified to determine if that post was aimed at me......But I do know that rockets are lifted differently than serpent shells. I also know that a 2" shell of serpants would aproximate a golfball full of earthworms.....really cool looking, except to the audience..........................

Regards, Stay green,

Bear

[Matt]

Oh i dont know, i suppose im going to actually have to make one in an attempt to prove you wrong.... hehe. Might make in 3 inch bah, its too hot to think.

-Matt

[Phoenix]

I said I was going to try crimping them, and I think I have found a really fast way to do it...

Previously, I found that actually crimping the sides of the case in didn't take that long, it was tying it off that did. However, I've found a way around that. I will attempt to explain:

1) Take a 1/4" brass rod, with flat, level ends. The last part is important.

2) Dry roll a long case from newspaper, pasting the inside and outside layer. There are two reasons for pasting it to the rod. It helps it to lay onto the rod and makes it easier to roll, but it also stops the inner layers of paper from collapsing when the tube is crimped later. In my case (no pun intended) the case walls were about 1.5mm thick. This worked well for me, though you may need to experiment.

3) Cut the long case into the desired lengths on the former. I cut my 30cm long case into four.

4) Slide one of these so that about 1.5cm overhangs the end of the rod.

5) Wrap about 3 or 4 turns of 10lb fishing line around the case, 1cm from the end of the case (and 0.5cm from the end of the rod). Note, this is a "wider" crimp than usual and is essential for this method.

6) Pull this tight* and rotate the case, as you do, to crimp it. It is very important that the end of the case nearest the crimp is intact and has not collapsed. It should look something like the case of the serpent on page 112 of "Pyrotechnics" by Weingart.

7) Remove the line, but Leave the case on the rod. Gently slide the case down the rod until the crimp is resting on the end of the rod (try not to open the crimp up though)

8) Press the crimped end of the case against the table top. What should happen is that the narrow crimped part will be forced down into the empty 1cm of case at the end. The end of the rod pushes it down into the bottom of the case, rather than it having a 50:50 chance of going up into the main body of the case. The result is a crimp that will not only keep its shape, but cannot be pushed open from the inside. From outisde, the crimp will not be visible. There will just be a crease around the tube where the bits either end of the crim meet. It may take a bit of practice tho get the hang of doing this without just crushing the end of the tube.

9) The tube can then be placed on a pin to be filled with propellant. A bit of priming can then just be applied to the end of the crimp (inside the bottom 1cm of tube) and touchpaper applied, or a core can be made with an awl. I haven't flown one of these yet, but the nozzles have performed fine in static tests.

*The way I did this was to sit at a table (for rolling the cases) and tie one end of the fishing line around a dowel, which I then put under my legs, so as to have the fising line emerging from between them. To crimp the cases, I held the case in my left had and tightened the line with my right. Make sure the dowel is plenty far enough forward before you pull the line tight - It's kind of sharp

Troubleshooting:

If the end of the tube just collapses, try using a thinner tube or kind of rocking the tube as you press, to encourage it to fold into itself.

If the coke is too wide, use a thicker tube, as it is the layering of the tube walls that causes the reduction in the size of the hole.

If the crimped section pops out of the emtpy "collar" that you force it into, the crimped bit probably wasn't long enough. Use more turns of fising line.

Finally, I don't know how clear it is how the finished case should be. If anyone is interested I'd be happy to do a few drawings which someone might host (Stuart?)

[EDIT] Here's the picture

Edited by Phoenix, 03 April 2004 - 10:22 PM.

[Stuart]

Send Send Send

[Phoenix]

Thanks Stuart. Can you send pictures with the forum's email feature? I couldn't. I sent the picture as an attached Word document to your Hotmail address instead.

OT: Who watched the Brit Awards? The Darkness were good, but Muse should have won Best British Rock Act.

[Stuart]

I havent recived the e-mail yet and its 4:30pm. If it isnt here later I will PM you to let you know