Stronger bp fuel grain

[NeighborJ]

I am playing around with different spindle size in my nozzleless 1# bp rockets. I've made a tooling set with a 1/2" spindle approx 8" long and am very impressed by its performance. However it does not come without some downfalls. The motor launches as if it was shot from a gun with a deafening hiss which has a tendency to shredd my bamboo sticks. The more important issue is the fact that I can hear and see small chunks of fuel grain being ejected out the rear of the motor. The grains start at 1/8 thick near the nozzle and are rather fragile. I can use my good sugar pine sticks to fix the de sticking issue, but I was wondering if anyone has experimented with a red gum bound (hot) bp mix even if it is only used on the first 1-2" of the spindle?

Open to any suggestions,thanks.

On second thought the two problems may be related. If the stick rips off it could be warping the tube as it does so. I use fiberglass reinforced tape and hot melt to attach the stick.

Edited August 1, 2016 by NeighborJ

[Seymour]

I haven't used Red Gum as a binder so I can't comment on that, but I feel like when I add a little bit of wax to BP to reduce dust and make it easier to work with it also produces stronger grains when pressed, but I have no data to back this up.

 

I don't know how well these are compacted but if you press them so hard that they need a sleeve to prevent the tube splitting I feel like it will help, unless you are already doing this.

 

Hope you get them going as you want soon

[Arthur]

Skip the hot melt glue! Any rocket motor worth firing gets hot enough to remelt that glue then the stick is free to wander. White PVA glue is cheap and usually sufficiently heat resistant, it just takes time to dry. Don't try to rush things, in pyro it often bites back.

[dagabu]

Skip the hot melt glue! Any rocket motor worth firing gets hot enough to remelt that glue then the stick is free to wander. White PVA glue is cheap and usually sufficiently heat resistant, it just takes time to dry. Don't try to rush things, in pyro it often bites back.

 

Every morning at PGI, I clean up the rocket field of sticks and duds (returned to safety) and of all the sticks I find with the tube still attached to them, the ones with hot glue and fillets on the stick sides, are dominant. I must have handled 100k of sticks in the past decade. White glue has a very low sheer load, it they are tied on as well, I will find them attached but not firmly. Tape and hot glue make for the very strongest bond and I have to spend a LOT of time pulling the tubes off of them and often have to make two cuts along the fillets to de-bond them.

 

Yes! DO use hot glue, add fillets to the sides of the stick AND use twine or tape as a secondary method but please skip white glue, super glue and other low sheer glues when attaching sticks.

[NeighborJ]

Thanks for the replies guys. I've finally been able to download the video to my sons computer and the slow-motion clip was very telling. One frame the rocket is just starting to lift and the next frame the rocket is at a 30 degree angle to the stick which hasn't left the launcher yet. The next frame the rocket is gone but I can see burning bits of fuel grains streaking past.

The motor had been hand rammed as I feel that the repeated agitation of the hammer creates a more consolidated grain, at least for this size motor. The increments are started out very small (1/8") at the nozzle then gradually increased to around 1/2" near and above the top of spindle. Split PVC, hose clamp support.

I truly believe the problem will be fixed with a better stick. The problem may never have arisen had a weighted header been attached. I've used this spinde design on 4# and 3# motors and was a sound platform, however ,looking back I did have problems with broken sticks on those as well but it was a lesson I learned about proper stick length and balance. I am planning to test a tapered pine stick tonight if life doesn't get in the way.

I am however still interested in the possibility of a red gum bound bp rocket fuel. I read a post about it here mabe 3 or 4 months ago outlining some formula from a book but I've had no luck finding it since.

[Sparx88]

Hot glue and fiberglass reinforced tape works just fine.

Not one was that have been found didn't have the stick still attached.

[dagabu]

Thanks for the replies guys. I've finally been able to download the video to my sons computer and the slow-motion clip was very telling. One frame the rocket is just starting to lift and the next frame the rocket is at a 30 degree angle to the stick which hasn't left the launcher yet. The next frame the rocket is gone but I can see burning bits of fuel grains streaking past.

 

 

This phenomenon is due to the inertia the motor is making and the still motionless stick pulling at each other. One widely used workaround, is to just use two sticks! 180° apart and shorter, skinnier than normal. With a heavy load, the acceleration is slower causing less "torque" on the stick.

[NeighborJ]

I've considered the second stick idea before with the larger motors but it wasn't crushing the motor at that time. My whistles also suffer from this problem often bending the stick at the launch and and cruising away at mach 10 in the wrong direction. This seems like a good solution to remedy all the high torq motors. It still needs to be balanced behind the nozzle correct? Another solution would be to call hobby horse and get the 3/16 heavy wall tubes but it may only solve one problem. It's a bit like treating the symptoms and not the problem.

[NeighborJ]

Pyrotechnician I have used paraffin wax with an acetone solvent for making slow bp in nozzled rockets and whistle. I have to admit it does press well but it burns too slow for my nozzleless spindles. I have had better luck using 2%glycerin it hasn't slowed the burn rate. I also use the glycerin to desensitize flash works great. Just keep it away from permanganate not that I would use it. I am looking for something which can be pressed and will then set without slowing the bp too much.

[OldMarine]

I use 2% paraffin in my fuel and can't say it's slowed it noticeably and if it did the improvement in handling and consolidation would negate it. I haven't tried mineral oil yet but plan to as soon as I can get time to go to my milling site to crank out a few pounds.

[NeighborJ]

MINERAL OIL, I don't know why I've never tried it in bp. I had problems in whistle using paraffin ,no whistle and lots of chuffing so I switched to mineral oil and it works awesome now. The tests I'd been doing with the 1# long core had no binder whatsoever, the nozzleless motors simply didn't need it until now. If the double stick thing doesn't work on that motor I will definitely try mineral o. I fired a 1# whistle in a stinger tube with the two sticks at dusk and it went exactly where I pointed it, guidance issue solved.

[DavidF]

Pyrotechnician I have used paraffin wax with an acetone solvent for making slow bp in nozzled rockets and whistle. I have to admit it does press well but it burns too slow for my nozzleless spindles. I have had better luck using 2%glycerin it hasn't slowed the burn rate. I also use the glycerin to desensitize flash works great. Just keep it away from permanganate not that I would use it. I am looking for something which can be pressed and will then set without slowing the bp too much.

 

NeighborJ, maybe you made a typo above? Paraffin wax does not dissolve in acetone. Did you mean naphtha? If you did use acetone, I can't see how it would work. I use wax in whistle all the time and it works well for me. DJ used mineral oil in his nozzleless BP rockets but switched to wax when he had a rash of CATOs after storing a bunch of motors in a hot trunk. A friend of his told me this.

 

You can used waxed BP propellant only for the first increment or two, if you like. Also: twisting off a long motor is easier than pulling it off. The grain has less tendency to crumble when the motor is twisted off.

[NeighborJ]

I don't know why but when I mixed the paraffin in the acetone it turned cloudy. Not all the wax dissolved but I'd say 80% did and that's the stuff I used. The wax was from tea candles. Mabe it wasn't tru wax?

The spindles I made have a thread under the base which I can turn forcing the spindle to retract up to an inch. The cracked grain was caused by the torque flex of the stick at takeoff.

[OldMarine]

If the takeoff is tearing your tubes you might oughtta look at tubes first. Whose tubes are you using? I've built 3 lb rockets with hot 75/15/10 with no binder or lube other than alcohol to granulate that left the tube so fast I thought they'd Cato'd until I looked up farther.

[NeighborJ]

OM.I think there is a misunderstanding here. The rocket motor is a 1# nozzleless motor with a 4# spindle, wall thickness is 1/8", length 10",stick was bamboo.

When the rocket ignites the thrust causes the motor to kick violently toward the stick causing the stick to bind in the launch tube. The tube does not tear or Cato but rather flex the tube enough to dislodge pieces of fuel grain nearest the nozzle. The bamboo will flex too much.

These are good quality tubes from hobby horse but when I ordered them Jim said he has 3/16" thick tubes as well if the 1/8" tubes are not strong enough for what I'm using them for. If I can attach a second stick to the other side of the motor as Dagabu suggested it will fly strait, never causing external stresses on the tube thus eliminating the need for stronger tubes.

Now that being said, I still have yet to test the double stick guidance on that motor but i have used it on a whistle motor tonight which had a tendency of torque flexing also. The whistle flew strait and true.

I am also still looking for a red gum acetone bound bp formula to experiment with even though it wasn't the solution for this problem.

[OldMarine]

Ahh, I missed the binding part. Ned Gorski uses 2 full length sticks on his more powerful rockets to great success but I haven't had need to try more than a short second stick to balance the drag after it leaves the tube. Good luck.

[NeighborJ]

Pyromaniac,

I am grateful for you shedding light on the wax issue. I've found the package of tea lights and nowhere on it is an indication of what it is made from, I can't believe I missed that. I was aware that naphtha was suggested as the solvent and it makes sense because paraffin is a petroleum product but I used acetone anyway sometimes I become mentally handicapped♿.

I don't know what the candles were made from but they didn't have the desired effect in any comp I've used (smokes, binders, and whistles). I will need to locate some real wax and try the whistle again, but only after I use up the 1 kilo I made the other day.

On the other hand if you ever need a wax which makes comps really hard to light and makes whistles choke like they have a pic of chicken in their throat I've got the stuff for you.

[DavidF]

NeighborJ, I really don't think it's the wax. I use tealights too. I've used them for BP, whistle, and waxing tubes, with no issues. The issue is the distribution of the wax, IMO.

 

If you melt the appropriate amount of wax in a tin can, and add the naphtha (away from the heat source), you will get a clear solution. It should be used immediately. If you leave the solution to cool, it will become cloudy and ugly.

 

Myself, I use about a cup per pound of BP. This is to get the wax to evenly distribute throughout the mass, and to keep down the dust later. You can use less, but it's a bit harder to work in, and the propellant will be more dusty in use because it doesn't rice as cleanly. It has been suggested to use less for whistle. I don't make near as much whistle as BP, so I haven't actually measured what I use with whistle. I probably do use less.

 

With very powerful fast motors, I take 2 sticks, tape them on with filament tape, and also tape them together at the bottom. I then launch the rockets from a short cardboard tube thoroughly taped to a stake, which is driven into the ground. When I used 2 sticks just dangling freely, my most powerful rockets (3#) would snap off the stick that was in the launch tube. If the motors didn't look like bobbleheads due to the large headers (6" ball shells), the sticks might not have snapped. The method I describe has been criticized as being potentially unsafe. But, the 2 guys that I know that have tried it say it works perfectly every time. I'm not aware of anyone with experience launching that way that has had a problem.

[dagabu]

You would be surprised how little stick is needed when using two or even three! 2012, there was a couple competing that uses a single stick, cut it into three equal lengths and glued it onto every one of their competition entries. A 3 pound whistle with a 4" heavy ball went straight as an arrow and the 1 pound whistle with a Ti tail and small report did so as well.

 

Three 16" sticks... Imagine!

 

This is a LONG fight with others but time after time, I show the folly of the long stick, all sorts of stability, yada, yada, yada. Here is a video of a 1 pound BP rocket with a 4 oz ball shell, just three fins and a 6" guide rod. No stick, the fins are 4" long.

 

https://youtu.be/gqkxTemDQ-0

[NeighborJ]

Now fins those are something I am much more experienced with. Coming from a strong background in amateur rocketry those are easy to get flying strait and they don't need large fins either. If I have doubts of its stability I can always tie a string at its center of gravity and swing it around in a circle above my head. And because the center will shift as the fuel is burnt it's a good idea to duplicate the test with an empty motor and same header. This will guarantee a stable flight. It is also not a great idea to make large swept back fins on fast motors because they can rip away due to shear forces of turbulence. 3 delta fins are usually adequate.

[dagabu]

I come from HP rocketry myself, in garage magazine and all until the AFT, in all their wisdom outlawed APCP motors (effectively). I moved on to pyro and haven't looked back.

[NeighborJ]

OK Dag you've converted me. Just got back from the test site where I set off 6 1# whistles and 3 1# long core bp motors. I did the comparisons of the double stick on the whistles, all double sticks flew laser strait until they slowed for apogee. The single sticks wobbled and went off course.

The original problem on the bp is gone and I think I'll need to lengthen the delay because they went so much farther then the single stick ones.

The last whistle got a 120g titanium salute that looked amazing.

[dagabu]

I watched Ned Gorski attach FOUR sticks on his enormous lampares this week, "laser straight" flights... 200' up.

 

I also watched as an old snort had my son (safety at the rocket line) launch his #1 hot whistle rocket, it had a single, 16" long, 1/2" x 1/2" stick on it and it flew completely straight. The balance point? about 1/2 the way down the motor!!!!!

 

Screw convention! Try what you THINK may work, espearmint!