Core = BOOM

[z92]

Hi!

 

I am new to rocketry, and I was told that my rockets need a core to be "very nice". Well, I started out by using some spiral would 1/4" id tubes and created rocket tooling for it - with a 7/10 of the tube's Length spindle.

 

Boom. both bentonite clay plugs flew out.

 

I decided I needed thicker plugs.

 

Boom. Tube blew up, nozzle intact.

 

I reinforced the tube with very strong tape.. boom, plugs flew out.

 

I decided to try and make an end burner.

 

Yay! It flew up in the air! Crazy.

 

I decided to roll some tubes myself, so I wouldnt have to deal with the weak spiral problem. These are aprox. 3/4" id.

 

Made one with about 3/4" or 1" clay plug.. but only about 4/10 length core. (Drilled.).

 

Boom. Both plugs flew out (fire came out of both ends) and the rocket stick was nailed into the ground... oops.

 

 

My black powder is not milled - its hand pestled in a mortar/pestle for about 30 - 60 mins.

 

Nozzle = 1/3 of tube ID.

 

All the end burners (no core but has a nozzle.) I have made has been flying into the air.

 

Willow charcoal airfloat + fertilizer KNO3 + Sulphur.

 

 

So embarrasing when these explosions happen infront of your family.

 

 

 

Thanks

 

Oh heres a video of a 3/4" id rocket (often refered to as an "m80" tube) that I made. Endburner:

 

My dad was recording, but he only got the start of it.. it flew very high.

[z92]

Oh may I add.. I am using the formula recommended for gunpowder (74:14:12 I think). But making a weaker formula just to have a core seems immensively stupid to me? Why not just make an endburner, then?

[TheSidewinder]

The most likely reason is that you haven't compacted the powder enough, either from using too-big increments or not compacting each one enough.

 

In anser to your question, straight "normal" BP actually IS too "hot" for many coreburners. Try 70-20-10, or 65-25-10. It's what a lot of BP rocketeers use.

 

With a coreburner and standard hot powder, its hard to compact it enough to prevent a CATO, unless you have a good press and use a sleeve on the tube.

 

 

Are you ramming or pressing? I suspect ramming. If so....

 

First, you need to use top-quality tubes if ramming, only because they take more abuse from the RAMMING than from the FIRING.

 

Second, you need a good, heavy hammer. A true dead-blow is what I prefer, but others dont like them.

 

Third, use small increments. For a 5/8" ID tube, I use an empty .38 calibre pistol casing and fill that about 2/3 full for each increment.

 

Fourth, take 10-12 strong, but not crushing, whacks with the hammer on each increment.

 

Ideally, the tube should bulge just a TINY bit up its length for each increment when you get it compact enough.

 

It's a fine line between "correct compaction" and "Oh hell, the tube split!!"

 

Good luck.

Edited March 9, 2008 by TheSidewinder

[z92]

The most likely reason is that you haven't compacted the powder enough, either from using too-big increments or not compacting each one enough.

 

In anser to your question, straight "normal" BP actually IS too "hot" for many coreburners. Try 70-20-10, or 65-25-10. It's what a lot of BP rocketeers use.

 

With a coreburner and standard hot powder, its hard to compact it enough to prevent a CATO, unless you have a good press and use a sleeve on the tube.

 

 

Are you ramming or pressing? I suspect ramming. If so....

 

First, you need to use top-quality tubes if ramming, only because they take more abuse from the RAMMING than from the FIRING.

 

Second, you need a good, heavy hammer. A true dead-blow is what I prefer, but others dont like them.

 

Third, use small increments. For a 5/8" ID tube, I use an empty .38 calibre pistol casing and fill that about 2/3 full for each increment.

 

Fourth, take 10-12 strong, but not crushing, whacks with the hammer on each increment.

 

Ideally, the tube should bulge just a TINY bit up its length for each increment when you get it compact enough.

 

It's a fine line between "correct compaction" and "Oh hell, the tube split!!"

 

Good luck.

OK - I am ramming. I used a teaspoon-full every time i rammed.. (the 3/4 id )

 

What are the advantages of cored rockets? End burners seem very strong to me. (my guess would be it is needed if you want to add sparks or..?)

[TheSidewinder]

With a proper press and sleeve, you CAN use much hotter fuels with cored rockets.

 

They can lift a heavier load, too. Find some graphs of cored vs end-burning rockets and look at them.

 

Someone more knowledgeable should be able to help you more.

 

Where's cplmac when I need him!?!?!

[hst45]

Since core-burners expose more fuel to the flame, your core-burners need a much slower burning fuel all other things being equal. 60/30/10 is a good starting point for core-burners instead of the typical 75/15/10 of your usual BP. Opening up the nozzle diameter can work too, but since your tooling is already set the fuel is the place to experiment. I can sympathize; most of my early rocket efforts I refer to as "salute-on-a-stick" designs.

 

I know that this has been talked to death before, but try cat litter, particularly Fresh Step brand, as nozzle material. Beat the hell out of it so the tube JUST starts to deform and you won't believe how much better your nozzles will be. Ramming works great for me up to 1 lb. motors (3/4" I.D.), although pressing seems to offer much more consistency.

 

Good luck, but a word of caution.....once you get them dialed in properly, these little guys are addicting.

[z92]

Since core-burners expose more fuel to the flame, your core-burners need a  much slower burning fuel all other things being equal.  60/30/10 is a good starting point for core-burners instead of the typical 75/15/10 of your usual BP.  Opening up the nozzle diameter can work too, but since your tooling is already set the fuel is the place to experiment.  I can sympathize; most of my early rocket efforts I refer to as "salute-on-a-stick" designs. 

 

I know that this has been talked to death before, but try cat litter, particularly Fresh Step brand, as nozzle material.  Beat the hell out of it so the tube JUST starts to deform and you won't believe how much better your nozzles will be.  Ramming works great for me up to 1 lb. motors (3/4" I.D.), although pressing seems to offer much more consistency. 

 

Good luck, but a word of caution.....once you get them dialed in properly, these little guys are addicting.

I know how addicting fireworks is . I am going to bentonite clay + fireclay + parrafin wax some time. I was told it's good. I think I will try the other mix you mentioned, But I am going to have lay down a little on the "experimenting" for a few days... I lack sleep because of it! And my parents are getting worried. To be honest, I dont blame them... one week where me and my dad filmed something 6 out of 7 days seems a bit extreme to someone who's not interested in pyrotechnics.

 

Good night

[asilentbob]

You could try nozzle-less... just a cored rocket... but you only press in BP, no nozzle mix.

 

IIRC for this using all airfloat chems, and polveroning them to cut down on the dust is normal. You might be able to polverone with a bit of added course charcoal or something to slow the burn rate and use it to cut down on dust too. I don't know.

 

Just vary one thing at a time.

[TheSidewinder]

A way that I found to almost eliminate dust is to take my base fuel after milling and add just 2-3% Dextrin (you can use SGRS, Guar, Gum Arabic etc but don't use more than the 2-3%), use NO alcohol, and get the batch a bit OVER wet.

 

That's because I rice it through a 50 or 60 mesh screen to produce miniscule granules, and it's hard work to push it through.

 

If it isn't wet enough it's almost impossible, and it won't form distinct granules when it dries, it just crumbles.

 

Lay out a LARGE spread of newspaper in the sun and granulate the BP evenly on it. Then LEAVE IT ALONE until it's completely dry. Don't "turn it" to dry it faster. It will get dusty.

 

The last batch I did, I ended up with grains about the size of commercial 2Fg. More importantly, they were all free-flowing and dust-free.

 

The smaller the grains when you ram, the better compaction you'll get.

 

 

You said you use a full teaspoon increment on a 3/4" ID tube?

 

Hmm... I'll let someone else say for sure, but I *think* that's too much. I haven't pounded any 3/4", only 1/4", 1/2", and 5/8", so I'm not sure.

[Sylar]

I think the best way to deal with the dust is preventing it in the first place by using another way to grind down your chemicals. Like a ball mill or a blender (pulse 5 secs, let it cool 2-3 minutes cycles!) and then just wait for all the dust to settle before opening it, or open it outside.

 

This way you will also get a more consistent powder then making every bath by hand grinding, which makes better and funner experimenting!

 

A teapsoon increment is a few mm in a 3/4 diameter tude, so that should be okay. But pressing is just better.

[asilentbob]

Sylar, we meant more the dust that often creeps out of the motor while you are pounding increments. When you don't use meal there is much less of this dust.

[moonshot]

I like to mill my propellant mix 4 to 5 hours and then granulate it without dextrin. I use a water alcohol mix like 80/20 and add just enough moisture to the comp to get it to clump into a firm ball. then screen it through a 15 to 20 mesh strainer.

http://i107.photobucket.com/albums/m314/di.../Picture134.jpg

The result is a 200g batch of propellant that will make quite a few smaller rocket motors.

http://i107.photobucket.com/albums/m314/di.../Picture135.jpg

Believe me I have rammed motors with both air float and grained powder and grained is way less messy.

[Aquarius]

Like many others here, I use granulated BP in my drivers. But I have a different way of making the grain harder and with less floating dust..

 

If any of you have read David Sleeters book about making amataur rocket motors, there is a hint where he makes his motors with a bit of binder(I use red gum) and alcohol.

 

When making my fuel, I add 3 % of red gum, mill the stash and granulate using water. Water will not affect the red gum.

 

When my granulated fuel has dried, I add 6 % of acetone and mix well. The bp is now sligthly wet, but still granulated and no dust. I ram my drivers, and after a while the acetone has vaporized out of the motor. When comparing "normal" grains to the red gum grains, the ones with alcohol/red gum is much harder and less prone to crack. And my drivers are very uniform in the terms of thrust and impulse. They do need some drying time, but I have no more CATO's..