Beginner questions for first nozzleless BP rocket

[DonCopal]

Hi folks,

 

I am planning to build my first 15mm nozzleless BP rocket soon. I already have a standart coreburner tool, that should work fine, shouldn't it?

So, I have some questions that I wasn't able to answer myself:

 

-Do I really need to mix mineral oil into my black powder? If yes, should I mill it in or should I dissolve it in acetone and then dampen and granulate the powder with it (like with whistle mix)?

-Shall I quickfuse the core or just put in a piece of visco?

 

Best regards

DonCopal

 

[MrB]

Both answers really cant be given by anyone but you. They depend on how hot your BP is.

 

If you use straight BP, no mineral oil, it will burn faster then with mineral oil. If you can top-fuse it, and it doesn't CATO, your fine.

If it does CATO, you will need to start figuring out a way to either slow the BP down, or try not top-fusing it. Neither might be the perfect solution.

Mineral oil is mostly there to slow down the BP. It also removes dust issues, so it's cleaner to work with. And you probably do want to thin it to get it worked in to the whole volume. Ive seen anywhere from 1 -5% recommended, (The % depends on what kind of oil you ultimately decide to go with, if any, what kind of charcoal you use, since different charcoals seams to adsorb different amounts, and how much you need to slow down your BP.) and your not going to easily be able to work that little evenly in to all your BP, so a solvent is the way to go. I would use lacquer thinner, but anything that will dissolve your oil, and then evaporate, is fine. And, of course, the % used oil is before adding the solvent. 3% supposedly is a good starting point, but the only way to know is trial and error

B!

[Col]

I would make one without oil and test it upside down. If you can run them without oil you`ll get more out of them. If you can consolidate the grain well enough you can tone the bp down with extra charcoal instead of oil. 80 mesh will add to the tail.

[DonCopal]

Thanks for the anwswers! My BP is very fast: https://youtu.be/oF-_9ragw9U?t=1m So, is it likely that I have to mix in oil? I've also heard that it's better to use oil anyways because it might crumble out otherwise.

[schroedinger]

Don you have to test it, but most likely you won't need the mineral oil. You can also use wax or vaseline if you meed it.

 

But you have to be carefully to apply consisten and good pressure and make sure that your bp compacts into a hard and solid grain. E.g. paulownia can pose problems since it is fluffy and likes to relax after the appling pressure. Willow, alder, spruce and pine don't have this problem.

 

You need to run a fuse up to the top of the core, if you only j-hook them, you lose a lot of power.

 

Expect you 15 mm nozzleless rocket to lift up to 300 g rocket weight.

[DonCopal]

I will ram it by hand, so will the pressure be OK or do I have to press it?

[MrB]

Small diameter BP rockets generally are ok to hand ram. Small increments helps getting consistency.

Trial and error. Always trial and error, plan for the first bunch to explode until you dial them in. If they don't, great.

B!

[schroedinger]

No worries about hand ramming a 15 mm rocket

[DonCopal]

Ok. One more question: Will a rubber mallet do the job or is a hardwood mallet required? Because I only have a big rubber mallet.

[lloyd]

A fairly hard urethane mallet will work, but soft rubber will not work very well for 'ramming'. It will work -- just not too well. By dint of its elasticity, it slows the motion of the rammer too much.

 

You can accommodate that some by making your powder increments smaller.

 

Lloyd

[schroedinger]

For 15 mm the rubber mallet works.

[DonCopal]

Ok. But I've also thought of this: If I took a hardwood cube and drilled a 15mm hole into it half way through (with a flat ground of the hole), then I could just plug it on top of the rammer and use a normal iron hammer without damaging the tool.

Do you think it would work?

[mabuse00]

Forget the rubber mallet. It bounces to much.

 

 

If I took a hardwood cube and drilled a 15mm hole into it half way through (with a flat ground of the hole), then I could just plug it on top of the rammer and use a normal iron hammer without damaging the tool.

Do you think it would work?

I dont think so. I had such ideas to though. IMHO the wood will split very quickly.

 

Didn't you once mention you had an arbor press ready? Or is the working height not sufficient?

[schroedinger]

Mabuse for 15 mm rockets a rubber mallet is enough. I can tell you that from experience.

 

If you want to make your own mallet, i would rather drill through the whole head and anchor the handle by driving a thick nail into the top (so that the handle expands and is press fitted).

 

The head need to be made from a hard wood like oak and the handle from a flexible wood like ash.

 

But why do you want to go through that hassle, an easy dead-blow mallet cost 8 $ a better one 30. In the time you make your own mallet, you spend propabky more then if you just buy it.

[FlaMtnBkr]

With a nozzle-less rocket you should be able to use the hottest BP you can make without a CATO. If it does pop it will be because it's harder to get perfect compaction by hand ramming. If it do have problems light the core at the bottom and make sure your increments aren't too big. With hot BP it's going to take off like a bullet anyways and a piece of visco is easier than quickmatch.

 

IMO, oil is mainly to help consolidate the grain and not to slow the BP down though I guess you could tame it a little that way but it shouldn't be needed. It does cut down on dust though and makes a nice compacted grain. But once you get up around 5-6% oil the rocket will start to chuff which can be a neat effect but might not be what you want.

 

I've used a copper end cap on wood and aluminum dowels to help protect them and keep them from mushrooming out. But I don't think that will be enough to protect it from a regular steel hammer, though I never tried that.

[DonCopal]

Well, do I need a piece of quickmatch for topfusing or can I just wrap some tape around a piece of thin visco, bend the end to a hook and insert it into the core?

[FlaMtnBkr]

Just bottom fuse it. You can experiment with top fusing later. I guarantee you will have no complaints lighting it at the bottom. You will be too busy giggling like a school girl when that first one goes up to worry about where you fused it.

[lloyd]

He got that right. You won't see or hear the difference until you start putting shells on top. And before you get to that point, you need to be very sure about the reliability over all lighting regimes.

 

When you do go to top-lighting, you can use either one, but visco in a wrapper CAN tend to spit out and 'bottom light' even a rocket that needed top lighting. Better to use match in a thin tube, so at the least, the entire core gets lit at once.

 

Lloyd

[calebkessinger]

+5 ..

I have never top lit a rocket. Hundreds upon hundreds fired with just visco shoved in them. It works fine for me. I sure don't want to speed up the launch, I'm headed the other way. Trying to slow it down.

[mabuse00]

 

Mabuse for 15 mm rockets a rubber mallet is enough. I can tell you that from experience.

After doing a lot of 15mm rockets with rubber mallets and switching to a vice, I'd say no, it's not.

With the vice I've got much more consistence than with the mallet.

 

I must also add that the 7€ mallets where ruined after ramming 8-10 rockets per side

 

 

I would always topfuse my rockets, because my feeling is that it offers the best constancy in the engine's behaviour. Lighting right at the nozzle you never know how fast the fire will spread, especially if the fuel is oiled and not so fire thirsty.

[DonCopal]

Today, I've built my first nozzleless BP rocket. I used black powder with 3% oil (just to try how it performs) and topfused it. I rammed it using a rubber mallet. I'll test it later and tell you how it performed.

For topfusing, I shrinked a piece of 2mm green visco into two layers of shrink tube, it resists the heat and sparks quite well.

[DonCopal]

Unfortunately, it was a CATO. It didn't first start launching an then collapse, it immediately exploded with a sharp bang. So, should I:

-Add more oil?

-Use a hardwood or hard plastic mallet instead of rubber?

-Put the fuse to the bottom of the grain instead of topfusing?

 

I would prefer the last option as that would surely prevent future CATOs. But what payload could I then still load to it without topfusing? 150g maybe?

[lloyd]

The first two things that come to mind are: Not ramming hard enough, and increments that are too large.

 

A rubber mallet doesn't do much to help you with #1. You can change #2, regardless of the mallet type.

 

So long as gasses can get between the tube wall and the grain, OR if the grain isn't hard enough to prevent cracking under pressure, you're going to get CATOs.

 

Consider waxing your tubes. That helps a LOT.

 

(Dave Forster's treatise)

 

Lloyd

[MrB]

Try without the shrink-wrap. If it's still in there when the engine ignites, it's not going to let the engine exhaust out.

B!

[DonCopal]

But without the shrinktubes, it will just ignite at the bottom? I think it's not because of not waxing tubes or not ramming hard enough (I did as hard as I could) but because the core was clogged with the tube. But wouldn't there be the same problem with quickmatches? I mean, they have a tube around them, too.

Edited December 18, 2015 by DonCopal