Delay mixtures for rockets

[mabuse00]

This has probably been discussed before, but please forgive mew if I overlooked it.

 

Many people use fuel rich charcoal spilling propellants to create strong tails.
Since I had great success with nozzleless BP and whistle, and new techniques seem to allow
hotter fuels even with nozzled engines, burdening my fuel with technically useless additives is out of the question.

Yes I know - use external comets - but I prefer an internal solution.
Ideally something that can be riced/granulated like BP for convenient handling.

A lot of mixtures seem to have the habit to produce slag/droplets that like
to cling to the tube, or if one is present, build up at the nozzle and stay there.
Especially after the core is consumed and the pressure drops.
-> no visible tail

What delay mixtures do you prefer?
W39j seems to be the answer, but maybe there's something else / something better I dont know yet.

[justvisiting]

A path I've chosen to follow loosely is the one taken by TR, the rocket 'master'. He uses an extra long spindle, and a more charcoal-rich propellant to create a bushy tail. I've also used the same tooling to make nozzleless rockets, with 5-10% coarse charcoal incorporated into the granulated fuel. If I want to press using dampened, free-flowing propellant, I 'pre-densify' the dampened propellant by pressing it into soft pucks and crumbling the pucks through a coarse, heavy screen. The propellant can be stored in a sealed container for a few weeks, and used as needed. For larger rockets like 3lbers, the damp propellant will flow freely enough that 'pre-densifying' it is of no great advantage. However, semi-granulating it in this way helps keep the coarse charcoal distributed throughout the mixture more evenly, which makes for a nice, even-looking tail.

 

I'm pretty sure TR's rocket propellant only uses about 57% potassium nitrate oxidizer. The advantage of his long-spindled, low speed rockets is that they fly smooth and straight, wherever they are aimed. Of course, the longer the spindle, the more important it is that it's properly aligned in the tube.

 

EDIT: Oops, I didn't really mention 'delay'. TR uses win39j, IIRC. It looks good with the heavy charcoal tail from the propellant.

Edited November 8, 2020 by justvisiting

[mabuse00]

I agree with the extra long spindle, I already have one for 1lb.

 

Problem for me is that most commercial tubing is to short for that.

My feeling is also, that even using the longer spindle, with a waxed tube and proper methods, a nozzleless rocket can take straight 75-15-10.

 

Before I use extra charcoal, I would first omit the ball milling... and by then the fuel would be rather gentle, too gentle for extra charcoal.

 

With 15mm calibre this is even worse, and I dont have overlength tubes for them. They need hot fuel to carry decent loads, any dilluting costs payload...

 

 

 

Since W39j seems to be a well proven thing:

Do you ball mill that composition?

And does it work with pine charcoal, so a rather slowburning type?

 

 

 

 

 

[justvisiting]

mabuse00, yes, a long-spindled 1 or 3lb nozzleless rocket can take straight, undiluted 75-15-10, and has great lift. I wax my tubes also. In that case, I generally just use FeTi in my delay. with the 3lbers, I easily lift 6" ball shells to more than high enough. My experience with win39j is not enough to comment on it. For charcoal effect stars, I like a charcoal-tailed rocket. Bright streamers is when I use FeTi. For white effects, I'll use Ti in the delay for tail. I use glitter delays sometimes too, but only in nozzleless rockets. I like the tail to be similar to the heading effect, which is easy with my simple headers.

 

In the rockets I just flew a few weeks ago, I used milled paulownia from Fireworks Cookbook to make screen-mixed propellant, added 2 1/2% water, and re-screened twice. With a 12" long 3lb motor, I'm able to use a brass shimstock support without any cutting, other than radiusing the outside end of the roll.

[mabuse00]

I wish I could get those overlength tubes here in europe...

 

 

Anybody else comment on W39j?

Milling? Charcoal type?

 

Another question: I have 325mesh, 200mesh and 150mesh atomised aluminium - what would you prefer in this case?

Maybe rather a mixture of all?

[Mumbles]

A less popular suggestion is Chrysanthemum of Mystery with maybe 5-10% titanium. Coarse Al or MgAl would probably also work. It's delicate but very elegant and attractive. It's not particularly bright, so you'd probably want to pair it with BP type rockets so as to not overpower it or overpower your eyes.

 

I don't have a lot of experience with rockets. My general, albeit minimal, preference is to use mildly milled comps in the delay just to ensure they burn cleanly and completely. I'd probably go with a mix of at least the 150 and 200 mesh atomized aluminums personally. It will better represent what the formula was developed with. A mix of all 3 wont hurt either.

[justvisiting]

mabuse00, there was a rocket tube shortage scare a while back in the USA, and somebody sent me some pulpy tubes to test. I believe they were from Germany, and the brand name was Eger. The tubes I got were equivalent to what we call 3lb tubes over here. They are 19mm ID, 34mm OD, and 600mm long. I believe these tubes would NOW be suitable for rockets, contrary to the fairly common previous perception that only NEP tubes are good enough for rockets. I make this statement because it's a commonly held belief that high pressing forces are required to make reliable high performance pyrotechnic rockets, and these tubes might not be up to handling those forces. Now that the pressing forces can be greatly reduced through the waxing of tubes and dampening of the propellant, the Eger tubes might be just the thing. I found this:

 

Products – Eger Hülsen (eger-huelsen.de)

[shockie]

What us W39j?

[Mumbles]

Winokur 39 glitter modification j. It's a Tom Rebenklau thing. Basically it's win 39 glitter with 2.5 parts -60 mesh MgAl I believe.

[mabuse00]

@justvisiting:

 

They are 19mm ID, 34mm OD, and 600mm long

You meant 25,xx mm ID, right?

I know the eger tubes. But you have to take a large amount, they dont deliver en détail. If I ever need 3lb motors, that would be my choice.

I like how they eat up wax, like a sponge

Somewhat compressible though, so even with a sleeve there will be a little deformation.

 

 

@Mubles:

I finishes the batch before reading your reply, I used the 325mesh only. The formula posted somewhere states "120-325mesh" but it also states "20 micron".

 

Then I found my old notes, and remembered that 325mesh was fine, so I used it. With slow pine charcoal.

 

 

Milled 30minutes (distributed milling process) and granulated like rocket fuel It works as it should. Tests with nozzles are yet to be done...

[justvisiting]

mabuse00, good catch. Yes, I meant 25,xx mm ID. Yes, those tubes do soak up wax like a sponge. I've also found that cutting them on a miter saw kicks up an incredible amount of dust. It's like the tubes are made of dust! It's interesting how they make these tubes, compared to (say) NEPT. Eger tubes are made of pulpy, recycled paper, rolled with occasional dabs of non-water-based adhesive. There's very little glue on each tube.

 

It's true that there is compression of the tube when pressing at high forces. Pressing damp propellant into a waxed tube allows for less force to be used. As I recall, all the motors I tested worked well and looked good, even strobes.

[mabuse00]

 

Eger tubes are made of pulpy, recycled paper, rolled with occasional dabs of non-water-based adhesive. There's very little glue on each tube

That applies for many but not all of them.

 

I remember some time ago when I did my first rocket experiments I got some eger tubes that where much more plastik-like and in my opinion more suitable for our needs.

 

The problem is, at least thats my feeling, that the tubemaking people usually dont make them with our application in mind. The perfect tube would be plastic-like, hard, not pulpy, and would not be super thick, because it is used with a sleeve anyway.

With great emphasis on constant size, minimum tolerances.

 

Rockets like we make them are not produced commercially, and if, like the bigger ZINK models, they have special tricks for pressing, like a plastic or aluminium pipe embedded into a paper tube. The effect is the same like a waxed tube, eliminating the typical paper tube troubles we have. Thus the outer paper tube is no longer a crucial part.

 

In Europe, most tube reselling pyro shops do not not even understand that. It does not bother them, because it does not bother 90% of their customers. Most sizes aren't even available in the proper length.

And lets be frank, we know why that is. Its simply not important for making ground salutes

 

 

In case somebody is interested, my W39j makes 5mm/sec pressed @6000psi

Edited December 6, 2020 by mabuse00