Spin Stabilised Model Rockets

[Arkangel]

Flushed with the success of my recent rocket engine testing, I'm soon going to start putting some work into a project that's been on my mind for a while. I really fancy making a mini working version of this:

<img src="http://www.boomspeed.com/arkangel/minimlrs.jpg" alt=" - " />

Or a katyusha/MLRS type thing. For this, I need the rocket to be cheap and easy to produce, able to fit into a launch tube (ideally a battery of them:)), be electrically fired and have enough delay so that the burst charge ignites after it's hit the ground, rather than when it's in the air. To fit in a tube, it's hard to have a fin stabilised rocket, so the only choice is really spin stabilisation, and I wonder if anyone else has had success with these.

There are 2 ways I'm thinking of this:

1st, with the American 66mm LAW, there are some fins which fold up inside the tube, and are extended by springs at launch. I used to have a motor from one of those, and the fin mounting assembly is very complex to produce. What I have in mind though, is to have some small, flexible plastic fins Made out of tupperware material or something similar) glued to the base of the rocket, so that they could be folded over to fit into the tube. Angled slightly, when the motor left the tube they would pop back into shape, and then cause the projectile to spin. The main drawback to this would be making the fins - it's a simple enough idea, but bending something like that is not easy - assuming you want it to pop back into shape.

The other idea is to have two nozzles, quite close to each other, but angled to create the spin. The tricky part of that, I imagine, would be in making the nozzle plug strong enough to hold the pressure - an idea I had with this was to have an apprpriately drilled coin in between the clay nozzle plug and the fuel grain. When you drill the nozzles, you'd line them up with the holes in the coin, which would then bear much of the weight. (I could, of course, make a nozzle from something else)

(A variation on this 2nd method would be to have a main nozzle as normal, and then drill two tiny thrust ports through the nozzle plug to create the spin)

I don't know how much anyone's done with this. All the stuff I find on google is for fin/spin stabilised stuff, launched from a pole/pad, not a tube. Also, nothing seems to come up in the archives, so please let me know if you've tried anything like this:)

<small>[ March 11, 2003, 09:06 AM: Message edited by: Arkangel ]</small>

[Anthony]

Your second idea sounds a lot like the gyrojet, a bullet-like rocket designed to be fired from a smoothbore small arms barrel.

For springy fins, sections of 2L plastic drinks bottles might be better - cheaper, more flexible.

Glad you're having fun :)

[EP]

I've thought about doing the same thing myself, however I'm still waiting for my rocket supplies I ordered over 2 months ago! :mad:

I've tried making fins like you described with flexible plastic (only once though) and it worked quite well. Next time I will use a thinner and more flexible plastic because I used the plastic from a flexible 3-ring binder. Using the plastic from a 2L bottle is a good idea, it's even got a curve already!

Some Hydra 70mm rockets use a metal version of this idea, you can see it on the top rocket in this picture:

<a href="http://www.fas.org/man/dod-101/sys/missile/kphydra.jpg" target="_blank">http://www.fas.org/man/dod-101/sys/missile/kphydra.jpg</a>

The angled nozzles would also work, and once you have a good method of making reliable nozzles it would probably take a lot less work than making quality fins. Often to reinforce nozzles metal washers are used, they are already drilled. <img border="0" title="" alt="[Wink]" src="wink.gif" />

[Harry]

How small d'you want to make these rockets? If you make the payload larger in diameter, then the fins don't have to be folded at all--just make them same diameter as the payload. Couple years ago, saw a website where a guy built that sort of rocket, launched it from a tube. Raved about the power boost he got by using a closed breech. Link long since lost.

Harry

[Arkangel]

Gotta make proper use of my time Anthony;)

Yeah EP, those flip out fins are exactly what I'm thinking of, although I'd try to put more pitch on them to increase the rate of spin - that's one of the difficulties. I like the idea of a plastic from a bottle. I'm going to try gluing them to a rocket body, then heating them with a paint stripping gun, so that they assume their "new" shape. Hopefully, when they are bent over to fit in the launch tube, their tendency will be to spring naturally back into shape, without the need for springs etc.

I'm liking the twin nozzle idea as well. I'd thought about ramming the nozzle-end plug with the coin/washer embedded in it, then using markings on the rocket body, along with a drilling jig, to drill two nozzles consistently at the right angle.

Edit: Harry, we posted over the top of each other, but I think you were thinking of the dude from Xinventions, and this is the link regarding his launcher:

<a href="http://www.xinventions.com/main/pyro/model_rocketry.htm" target="_blank">http://www.xinventions.com/main/pyro/model_rocketry.htm</a>

I had considered something like that, but I think that looks like a piece of shit, I really can't see those fins having much aerodynamic effect, the "warhead" is far too large. Plus, the larger diameter, the harder for it to spin fast.

<small>[ November 11, 2002, 04:23 PM: Message edited by: Arkangel ]</small>

[Eliteforum]

The rocket looks like a dissassembled vibrator with fins! :D

<small>[ November 11, 2002, 04:11 PM: Message edited by: Eliteforum ]</small>

[Arkangel]

Personally it didn't strike me that way, but if it's what you're used to.................. :p

I don't want to have it too big. A motor with an internal diameter of between 1" and 1.5" is probably about the biggest I'd want. Anything larger would add quite a few complications to everything.

I'd like a rocket with a range of about half a mile. That would suit me, carrying a payload of 30g of flash. Ripple firing an 18 tube launcher would be the next best thing to the bb minigun in NBK's thread. :D

<small>[ November 11, 2002, 07:23 PM: Message edited by: Arkangel ]</small>

[Agent Blak]

The Gyro Jet would be the most interesting concept of them all. Sadly it isn't always the interesting that is the most practical. :(

You could make set of fins that use a sping and cable to snap them in to alignment. I have seen this idea used on car hood emblems.

The cable attaches to the fin through a slot. The spring provides the necessary tension to snap the fin into place and allows it to fold over. Then it leaves the tube there is no longer anyhing holding them down. If I were to do this I would employ a sabot style design to hold the fins in and create a better seal to assist the rocket inleaving the launch tube.

You could also just use a sabot style design to proect the fins; when fired the sabot simple sheads and the fins are in perfect alignment.

[Arkangel]

The main (edit:dis)advantage to the gyrojet is that it's going to create recoil in the launch tube, unless it's just like a recoilless rifle.

I get the fin idea, but it feels a bit complex. Some kind of plastic, using it's thermo retentive properties is probably the way I'll go initially. Springs and slots add substantially to the complexity of the design. I want to be able to make each one of these in 15 minutes.

Sabots are another good idea, but I initially discounted that because it adds to construction problems. Hmmmmmm.............I suppose I could just make some half rings out of the foam rubber they use to insulate pipes. Using the foam rubber and hibachi sticks I could have a sabot ring at the front of the rocket, plus one at the back, in front of the fins. Each side of the "sabot ring" is connected to the one below it by hibachi sticks, to maintain it's spacing, but not connected to it's partner "half" so they could split away on launch. If I sprayed the inside of the launch tube with WD40 it should launch ok. Not a favoured option though - if I can do it without I will.

Another edit: I've just checked out the Gyrojet on the web, <a href="http://www.hwth.com/guns/MBA_Gyrojet.htm" target="_blank">http://www.hwth.com/guns/MBA_Gyrojet.htm</a> and it looks as cool as fuck. I'd love the carbine version. I was also wrong about recoil, although I still think there'd be quite a bit of it.

It's interesting to consider how they made the projectile though. The base is the important part, probably with 3 or 4 nozzles for the spin, plus maybe a main one for thrust. The more I think about this, the more I'm leaning toward two angled nozzles, drilled with a jig, and with metal reinforcement to the nozzle plug

<small>[ November 11, 2002, 05:43 PM: Message edited by: Arkangel ]</small>

[nbk2000]

(Rod Serling ON)
Imagine if you will...
(Rod Serling OFF)

two pipes. One fits snugly inside of the other. Now, the inner pipe was, prior to insertion, cut in half. Not in a straight line, but rather in a spiral, like a toilet roll tube.

The rocket body just fills the inner tube, while still being able to slide freely inside.

At the base of the rocket is two small studs, 180 degrees from each other, that fit inside of the cut spiral groove of the inner tube.

Now, as your rocket is launched, the studs engage the spiral groove and impart spin to the rocket.

This is the very same principle behind the MLRS artillery rocket used by the US.

Now, add a shear wire to restrain the rocket within the tube till it reaches full thrust before launch, and you'll have one bad ass rocket gun. :)

Not on par with my Gy2 design ( :p ), but probably much cheaper to build. <img border="0" title="" alt="[Wink]" src="wink.gif" />

[Arkangel]

So if I get this right, the motor, once it's reached peak thrust, travels up inside the rocket body, doing so whilst forced to rotate by the inner (cut in a spiral) pipe. The rotational inertia of the motor then causes the projectile to spin as it leaves the launcher????????

By george, it might just work! Well, actually that sounds a bit problematic for me in manufacture, although I think I get the principle. Everything I build rocketwise will either be in very light Al, or Cardboard for the motors.

So that's really how MLRS works? Do you have any links? (I'm trying to get to an MLRS firing in the near future :p )

[Anthony]

The pipe lagging, discarding sabots is a brilliant idea, and one I will be trying! :)

I enterpretted NBK's idea a little different to what I think you have arkangel: The spiral tube is the barrel, and the pegs are on the outside of the rocket body. In effect a reverse rifling, where the "sticky out bits" are on the projectile and go into the barrel. Instead of the rifling going into the round.

IIRC, a very similar system was used on the first rifled canon.

[nbk2000]

<a href="http://call.army.mil/products/trngqtr/tq4-99/mlrs.htm" target="_blank">http://call.army.mil/products/trngqtr/tq4-99/mlrs.htm</a>

</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">quote:</font><hr /><font size="2" face="Verdana, Arial, Helvetica">
The initial spin is imparted to the rocket through spin rails mounted on the inner wall of the launch tube.34</font><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">I've been trying to find pictures, but no such luck. Though I've seen it in Air & Space Weekly.

Anyways, you're right anthony, the rifling is similiar to that of early artillery like the Armstrong shell that had raised studs(AKA "sticky out bits" :p ) that fit into grooves in the barrel.

<img src="http://www.civilwarartillery.com/images/iiia48.jpg" alt=" - " />

Imagine this is a rocket, and had only the studs at the bottom. That'd be an MLRS rocket.

<small>[ November 11, 2002, 10:01 PM: Message edited by: nbk2000 ]</small>

[Arkangel]

Ahaa, now I get it, I was overcomplicating things in my mind and assumed that the tubes you were describing were part of the projectile.

Anyway, from the same place you quoted: "The four stabilizer fins at the aft end of the rocket provide in-flight stability by maintaining a constant counterclockwise spin. The initial spin is imparted to the rocket through spin rails mounted on the inner wall of the launch tube"

So in addition to the initial spin, MLRS has folded fins. The Katyusha has a rifled barrel as well. I can see I'm going to have my work cut out with testing :)

[nbk2000]

MLRS also have to travel 40 miles. I rather doubt your rockets are going the same distance. <img border="0" title="" alt="[Wink]" src="wink.gif" />

[Arkangel]

"From little acorns grow mighty oak trees".

NBK2000, April 12th, 2002

<img border="0" title="" alt="[Wink]" src="wink.gif" />

[MrSamosa]

If you are having trouble with fin placement...perhaps you could put them in front of the rocket, on the warhead? In this case though, it would not fit all the way down the tube; rather, the warhead + fins would hang outside. I believe that I have seen some rockets before, I think on war planes, that have front-fins.

[0EZ0]

</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">quote:</font><hr /><font size="2" face="Verdana, Arial, Helvetica"> I believe that I have seen some rockets before, I think on war planes, that have front-fins.
</font><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">That is true... but they almost always have rear fins as well. Off the top of my head, missiles in need of high precision like air to air missiles have both rear and front/middle fins. The AIM-9 Sidewinder is on such example, a high precision close range air to air missile. For specs for different missiles and rockets check the bottom link :) .

AIM-9 - <a href="http://www.designation-systems.net/dusrm/m-9.html" target="_blank">http://www.designation-systems.net/dusrm/m-9.html</a>

Directory of U.S. Military Rockets and Missiles - <a href="http://www.designation-systems.net/dusrm/index.html" target="_blank">http://www.designation-systems.net/dusrm/index.html</a>

[Harry]

Yes, precision missiles have forward-mounted fins, but those fins are more control surfaces than stabilizers. On a "dumb" rocket, front fins are a liability to stability. A smart rocket is steering with those front fins. Gotta be maneuverable to hit a scared but skilled pilot!

Harry

[frogfot]

Isn't there other ways to stabilise rocket. Making weight (center of gravity) moved to nose. I know it's not that effective as fins, but if rocket gets enough high acceleration it will become stable in short time. Maby some fast burning fuel as BP will make it.
Those folding fins will probably help rocket to stick in the tube, or will be ripped off.

[Arkangel]

Well I was going to make the tubes slightly oversize, and lubricate them well, whatever happens, and I'd make a jig for glueing the fins very firmly in place if I do use them. Most modern adhesives are very effective if applied correctly

I don't know of any finless rockets, model or otherwise that use anything other than spin stabilisation, or a complex, expensive and extremely hard to create, gimballed motor assembly. Given my parameters, spin is the best bet. The choice for me is effectively fins, nozzles, rifling or a combination of all 3

[Arkangel]

A very helpful link from A43tg37, which might be really useful for this project :D

<a href="http://www.civilwarartillery.com/projectiles/rifled/FAOIIIa64.htm" target="_blank">http://www.civilwarartillery.com/projectiles/rifled/FAOIIIa64.htm</a>

<small>[ November 13, 2002, 04:25 PM: Message edited by: Arkangel ]</small>

[Agent Blak]

The problem I fore see with spin stableized projectiles is thatit has to rotate on a Y axis almost perectly to be effective. You don't want your rocket to wobble or cork screw in flight either(wastes fuelless accurate).

[Arkangel]

Agreed, which is why I'd like to drill any nozzles with a carefully machined jig.

However, since this is just intended for scaring the crap out of my dad from half a mile away, I'm not THAT concerned about accuracy :D

As long as each unit is constructed consistently, my accuracy with corkscrew trajectory or otherwise is going to be reasonable.

If I waste fuel, I just carry my launcher 100m closer to his house until I can land them all around him <img border="0" title="" alt="[Wink]" src="wink.gif" />

<small>[ November 13, 2002, 06:31 PM: Message edited by: Arkangel ]</small>

[EP]

That link (http://www.civilwarartillery.com/projectiles/rifled/FAOIIIa64.htm) looks interesting, but would it really be effective for a rocket? It seems like it would need a very high velocity (ie a gun) to get any decent spin, and a homemade rocket is unlikely to reach the required speed. Looks like it'd be at least worth a try though.

I'd like to see your dads face when you do this! :D

[nbk2000]

The confederates lost the war...'nuff said. <img border="0" title="" alt="[Wink]" src="wink.gif" />

Trying to spin stabilize a rocket using canted ports isn't something you're likely to succeed at. MBAssociates (Gyrojet) had military contracts and engineers to work on that very same idea...and they failed.

Getting the needed accuracy was near impossible while still keeping thr projectiles affordable enough to actually produce.

Whereas, barrage rockets (like yours) can use rail/stud spin stabilization quite effectively since you WANT a little spread in the pattern to ensure coverage.

If you can get the rockets to burn up all their fuel inside the barrel, this would also improve accuracy as it would reduce wind cocking since the projectile would be on a strictly ballistic trajectory the moment it left the barrel. This was another problem that plagued the old Gyrojets.

[Microtek]

I have made numerous experiments with small ( 12 mm ) spinstabilized rockets. They completely exceeded my expectations regarding speed, acceleration and accuracy. They were made as follows:

- A 12mm OD, 10mm ID Al pipe 25 mm long were closed in one end using simple epoxy putty, the plug being about 7 mm long. Care was taken to make the epoxy bond strongly to the wall of the pipe.

- Once the endplug had hardened, an axial hole 3.0-4.0 mm inn diameter was drilled through it using a lathe ( this is the only point where a high degree of accuracy is neccessary ).

- Two additional nozzles were drilled in the plug on each side of the axial nozzle with each having a slight angle to impart spin. These extra nozzles were drilled by hand with a precision hobby drill and were about 1.5 mm ( I experimented with varying ratios of axial/spinnozzle diameter ). It is important that the spinnozzles are very close to the axial nozzle, at least on the inner side of the plug. They can even be made to merge so the exhaust stream is divided into thrust and spin portions.

- A coring tool was inserted into the axial nozzle extending a certain distance into the rocket body depending on desired thrust.

- A whistle mix extracted from commercial fireworks ( probably consisting largely of KClO4/Na-Benzoate ) was poured into the rocket from the open end and compacted strongly with a stamping tool.

- The open end was closed with compacted Al-foil and sealed with plaster or epoxy.

- The coring tool was extracted and the rocket was ready.

These burned up their fuel in about 0.1 - 0.25 seconds depending on the length of the core and moved about 20- 40 m during the burn. They couldn't be followed with the eye once the fuel was gone and there was no longer any flame to focus on. Based on the ( conservative )estimates of burn time and distance traveled speeds were found to be at least several hundred meters per second.

[nbk2000]

Some patents you may find useful.

4,158,447

6,450,443

6,168,111

5,322,002

All various means of rocket stabilization via spin or fins.

[Arkangel]

Cool, thanks for the info guys.

Like the 66mm LAW burns all it's fuel in one go (and with a right old bang!), there are clear advantages to that, but I'm quite keen to have the projectile visible in flight, so if I do make it a real fast burn, I might include some smoke/trace comp as the delay prior to the burst charge. The other thing to consider is that I was thinking of making the launch tubes from something like PVC drainpipe or conduit. In a fast burn, how much pressure does the launch tube have to contain, how hot will it be?

Microtek, thanks for that, what you've described seems to be what I had in mind as the variation on method 2 in the first post of this thread. It's great to know that you've tried it, with success. Any drilling I do will be with a jig for accuracy. Do you think epoxy would hold in a cardboard tube (I normally ram the nozzle until the tube bulges a little), or would drilling the spin ports in a clay nozzle work (although I will try that this weekend)?

How did you launch them, what made you try, did they have a payload, do you have any pictures? :)

[Microtek]

I launched my rockets from a 25 cm long PE tube using various types of ignition. Most often simply a piece of fuse inserted into the main nozzle ( I never had any problems with less than all of the core igniting ), but I also tried using a coring tool with a built-in bridgewire and then just left the tool in the rocket. This eliminated the vulnerability to rough handling as the motor was completely solid; when the rocket was ignited the overpressure simply pushed the tool out while igniting the rest of the core-wall.
I also tried using a hollow coring tool with a blob of pyrotechnic sealant in the end inside the motor and a toy cap on the other end. I then fitted a plastic platter with a hole over the coring tool so the rocket looked like a .22 cal cartridge. It was fired with a toy gun using the same PE pipe as barrel.

Sorry no pictures... I considered video taping a launch once to get a more accurate measurement of the speed, but I never did it.

[nbk2000]

You can buy pre-rifled PVC barrels from some "spudgun" sites, like this one.

<img src="http://spudtech.com/images/products/pvcbreechsm.jpg" alt=" - " />

<a href="http://www.spudtech.com/detail.asp?id=10" target="_blank">http://www.spudtech.com/detail.asp?id=10</a>

At less than $20 for a 5' barrel, I don't think you could go wrong with that. The studs for the rocket could be screws with the heads ground down.

[Arkangel]

Well, I've been busy in the downtime, but not so successful. I did go to a local engineering shop and have them make me up a 1" version of the rocket tooling I got from Skylighter, the main difference being that I made it so that I can screw in different length coring mandrels. The mandrels are 6mm, but are a bitch to remove at the moment, so I need to get the engineering shop to put more of a taper on them - tried to do it with emery paper and an electric drill.

I'm having cato problems at the moment, 50% of the motors I've lit recently have just plain exploded. Here's a bit of offline dialogue from me to another forumite, if anyone has comments, please let me know. By the way, I use Sodium Chlorate because it is expensive enough as it is, without spending more money on KCl to convert it. I keep all my stuff stored with a dessicant if I store it at all.

"Anyway, regarding rockets, I did think about stinger type drilled holes in the side, but there were a couple of problems with that. 1st, you don't get thrust immediately from the side ports without lighting them first, then you have to wait until it's burnt through to the main core before you get forward thrust. Also, you run a stinger up on top of a spike, so it's already rotating before it lifts off. If I launched one from a tube, it would only start to rotate when it had left the tube, and would have a wide corkscrew track, if it was in any way stable.

I've had some tooling made up recently to 1" ram rockets with, and was experimenting a bit this weekend. I need to get a better source of nozzle clay than kitty litter - it doesn't work so well, and I'm running out of Bentolite. For the spin stabilised jobs though, I think what I'm going to do is use my existing tooling to press a grain without a nozzle. Then, put a little paper disk down the "business end", and then fill the end with cataloy filler - chemical metal or something similar. I'll also get a jig made up (I'll make a couple of trial ones from wood before I have them made in metal) to drill the nozzles. I plan to have one main thrust nozzle and 2 smaller angled ones outside it for the spin. (as described by Microtek)

I only made 2 rockets last weekend) with my existing fuel, 70/30 NaClO3/sugar. Both blew up and I need to work out a way of slowing them down. They had a 6mm full length core, so it might help to remove that, also, that ratio is a bit fast - assuming the comp is dry. I might try adding something like vaseline, oil, charcoal, or maybe even more sugar. Any suggestions would be appreciated.

(Without a core, that mix doesn't seem to produce much thrust, I thought about making them with a core, but then loosely packing it with some other kind of comp that will burn out slowly, and then allow pressure to build more gradually. "

Anyone got suggestions? :)

[Bubba]

As far as the pop-out fins I believe Skylighter was selling these a little bit ago. I wanna say they were spring-loaded. I'll try to track them down...
wwww.skylighter.com is the main site. Had the catalog with the info but lost it in a recent move... <img border="0" title="" alt="[Frown]" src="frown.gif" />

[Anthony]

Have you tried making "grog" with the cat litter? I think it should work a bit better.

Adding more sugar might give problems with slag blocking the nozzle, over oxidising might be better.

But I think the best way might be to use a wider nozzle to lower the pressure in the motor. You could use your existing tooling, but drill out the nozzle a little after the motor has been rammed.

I had a similar problem using NaClO3/sugar, no core and the thing never took off, long core and they CATOed. They worked if you limited the length of the core but only gave useful thrust for the length of the core, so flight time was pretty short.

[Arkangel]

Ahaa, now that's interesting, cuz you're describing exactly what is happening. I had been wondering if my fuel mix, or varying water content was part of my problem. Since you had the same trouble then I need to rethink my fuel. (just read your post poroperly Anthony, and I think I'll try the ratio in both directions - over and under oxidised)The way these things went, I very much doubt that nozzle size is the issue, they exploded almost instantly, rather than building up pressure and then blowing.

I'll try KNO3/sugar, but does anyone have more suggestions about slowing my NaClO3/Sugar down???

<small>[ December 05, 2002, 08:41 AM: Message edited by: Arkangel ]</small>

[vulture]

I would try 50/50 H3/NaClO3 + sugar as this seems to have the best of both worlds. Make the H3 with somewhat more coarse C powder.

I once made a large KClO3/sugar rocket with core and binded with dextrin but it shot out the nozzle with an insane burst of flames. It must have been a burn time of something like 0.5s for 50g of propellant <img border="0" title="" alt="[Eek!]" src="eek.gif" />

The 5mm thick clay nozzle was vaporized in the process, atleast I couldn't retrieve anything of it.

<small>[ December 05, 2002, 10:02 AM: Message edited by: vulture ]</small>

[Arkangel]

H3? - Isn't that charcoal and perchlorate? I'd certainly thought of adding some charcoal to my existing mix, but could you clarify? Cheers

[vulture]

H3 = KClO3/C 70/30
Burns very fast if very fine, but hasn't got a high impulse. By adding it to your existing mix you will decrease gas production and thus pressure build up, but you will keep the burn speed.

Hope that's clear enough..

[Sparky]

Kitty litter (the cheapest stuff - bentonite) doesn't work very well you say? My friend has had good results with it. He ball mills it beforehand, to make it well powdered, then pounds it very well. You can get different kinds of powdered clay (including 325 mesh bentonite) of course from the pottery store. Anthony said to try "making 'grog'" with your clay. To me grog is a powder to add to the clay in small percentages, to help it grip the side of the tube. This is a good idea if your failure mode is nozzle blow out. If the tube explodes then this is not much use, you need to slow down fuel, widen nozzle or get stronger tubes.

I guess Bentolite is a trade name or something?

About the KCl, - it is quite expensive if you buy it as a salt substitute. It can be had very cheaply in big bags as a water softener.

As for spinning rockets, my friend has found them to be quite stable. At least the small ones are very good with only one side nozzle. You do have to wait for the grain to burn through to get forward thrust, but meanwhile it is spinning up. Also, this rocket has the advantage of not needing to carry a stick with it. For complex payloads it is not very good because the spinning can easily throw off an unbalanced load.

For slowing down the fuel, I think fine charcoal is a good idea. It doesn't create any slag in itself, though it may indirectly. Also, slag is dependant on temperature and burn rate as well as composition i.e. if you ball mill a mix you will get faster burn rate so higher temp, so less slag. My friend has had no problems with slag ever, but believes other forumites that it may be a problem. Typically (especially in smoke compositions) magnesium carbonate is used to slow down burn rate. This is available from a pottery store, it is kind of expensive but 5% is a lot to put in a mix (makes it go much slower supposedly). Slowing down the fuel is probably a better option than making a smaller core. If you use a smaller core, obviously you get shorter burn time, so less height. Perhaps something that doesn't burn very well such as corn starch, dextrin or fumed silica (in small amounts) could be used for burn rate controll.

My friend tried charcoal/potassium perchlorate 70/30 but it burns quite slow. He thought since chlorates and perchlorates are similar it might work, but no.

[Arkangel]

Yep, Sparky, thanks for that, I think I will try some charcoal in the mix, just mixed in. I have some dextrin and chlorowax that I've used before, and some of those may be beneficial as a binder/colour/to slow it down. A full length core is really the only way with a single fuel type.

The side nozzle spinners (remember I have the stinger tooling and instructions from Skylighter) are a simple idea, but I believe they would be too unstable launched from a tube horizontally (or at least anything other than vertically)

[nbk2000]

They're likely to be unstable because they haven't achieved adequate spin to maintain stability before they leave the launch tube.

If, however, the rocket was to achieve full spin before launching, it'd likely maintain stability.

I'm seeing a spike at the launch end on which the stinger is mounted. The spike is attached to the launch tube is such a way as to not obstruct the spinup gases.

The rocket is retained in the tube by some sort of pin or such that allows it to spin until released.

I don't know if you could manually time it, but a 555 circuit could be used to ignite the rocket, count however milliseconds it takes for the rocket to reach full spin velocity, then retract the retaining pin, allowing the rocket to launch.

:)

[Mr Cool]

For small caliber rockets I'm sure it would be easy to set up a launcher that spun the actual barrel to the required speeds, and this would in turn spin the rocket. This way you wouldn't have to worry about making fiddly little nozzles / pop-out fins exactly the same on each rocket.
And its gyroscopic properties would keep it dead on target :) .

[Arkangel]

Spinning launch tubes, retracting pins - I get the impression you're making a simple idea quite complex here. Oh, and the other reason I don't favour the stinger type, is that there is no forward thrust from the spinning jet, so that proportion of the fuel is effectively wasted compare to directional nozzles in the base.

[vulture]

Here's a theoretical idea:

How about mounting a sheet of metal that's twisted 180° around it's axis over the nozzle? This should cause a vortex but I'm not sure if the rocket will start to spin. I would say yes, to compensate for the rotational movement but I'm really not sure.

Also, air might not be dense enough for the vortex to work, I believe it has only been tested under water so far.

[kingspaz]

how about a tube which has been flattened AND twisted. ok, take a metal tube and flatten the end but not all the way. flatten it to the point that its a kind of rounded rectangle shape on the end and the width you want the nozzle to be. now have a thick metal bar in the centre for the central nozzle and two thinner metal bars either side. then commence with the flattening to smack the gaps between the bars shut. remove the bars and weld the former gaps permanently shut. put the bar in a vice and twist the 'arm' one side of the main nozzle in one direction and the other 'arm' in the same direction (in relation to clockwise/anticlockwise) you should have a shape resembling an 's' on its side. well, a kinda flat 's'. the secondary nozzles on the arms should be diagonal now in relation to the rockets thrust axis (due to metal bending funny because the whole tube isn't flat). they would provide a compromise of main thrust and spin thrust so not too much is wasted. plus you have a main nozzle for the main thrust to come from. anyway, anyone think this would work? if made from steel i don't see why it wouldn't unless the pressure was too great and it blew open. this is what i would try if i had time.

[Anthony]

This is getting complex :)

How about... a rocket which fits the launch tube, so good gas seal and has a stick. The stick passes though a hole in the end cap of the launch tube.

Not a neat solution, but piss-easy :) You get a high rocket to launch tube size ratio too.

[Arkangel]

Bloody hell Kingspaz.....I finally worked out what you meant! <img border="0" title="" alt="[Wink]" src="wink.gif" />

I'm trying to avoid metal construction though, and steel would be expensive. I've sourced some 1"id cardboard tubes, and aim to get some metal or HPDE tubes just big enough to fit them for my launch battery.

Anthony, I think your idea, or a variation on it is a very neat solution, and one that I might try if I need a quick solution. Since I'm trying to replicate a katyusha, I won't be having a closed tube, I want a back blast out of the back of it. But if I mounted the rocket higher in the tube so the stick wasn't visible, It would look the part, and you might not notice the stick in flight - assuming it launched fast enough. Spin stabilised is the way I want to go ultimately, so sticks are a not in my long term plan.

But I'm really pretty set on the idea of a pressed core (when I sort my fuel out so it's reliable), with an epoxy filler end plug, drilled using the die that I'll make up. One of the attractions of this method is that I'd be able to press a load of motor cores, then make up a big batch of the filler and do a load of nozzles in one go, the closest thing I can get to mass production - which is what I'll need if I'm firing salvoes of 18:)

Hopefully over xmas I'll have enough time in my workshop to get this finally sorted :)

[nbk2000]

Here's a drawing to illustrate what I meant.

<img src="http://server3001.freeyellow.com/nbk2000/Rocket-Spin.gif" alt=" - " />

As you can see, it's VERY simple.

In fact, I think you could make it automatic.

The rocket would be retained by the pin until it generated enough thrust to push the cone against the resistance of a spring with slightly less pull than the rocket has thrust. Thus, when the rocket has spun up, and is creating near maximum thrust, it pushes the cone out of the rocket nozzle, causing the retaining pin to retract, releasing the rocket.

:D

Also, rather than having the rockets thrust pushing it, have it PULL the rocket. Make the nozzles towards the front of the rocket, aimed back and at a canted angle. This will both give thrust and spin at the same time. Much as was used in the Little John missles of the '50s.

[Arkangel]

I still don't believe you could spin the motor up in anything other than a vertical attitude. But you guys are coming up with some interesting suggestions. NBK wasn't the first Goddard rocket a dragger rather than a pusher? I would have thought that a dragger would have a degree of inherent stability with or without spin.

As a comparison, a few years ago, we were pissing about with some Estes motors, firing them just on their own from pvc conduit pipes. The first one we'd put a couple of layers of masking tape round the front and back ends so as to make it a neater fit. Trouble was, it jammed a couple of feet up the tube, unbeknown to our fat mate who had the tube over his shoulder. A flame was coming a foot or so out of the back of the tube, whilst he was straining his eyes to see it in flight. He worked out what was happening though, when the pvc pipe began to melt, and drooped onto his ass :) We tried again, next time without masking tape on the motor, and we got to witness an unstable and VERY angry rocket in flight. The closest thing I can describe are the bullets in "Who framed Roger Rabbit". The motor shot out of the tube, seemingly stable. About 50 yards away, and 50 feet in the air, it started rapidly changing direction, up down, left right and up again. This continued right throught the power phase, and as soon as it went into coast, it shot to earth, straight as an arrow, pushing out the tracking smoke.

So a pusher without spin, fins or a stick is ALL over the place. Ultimately, all I really want to do here is recreate a katyusha or MLRS, so if I had to use a stick I would, so long as the whole thing was contained in the launch tube. But that then complicates how I fire the rocket. It would be much easier to have the rocket base right at the bottom of the tube, with a bit of quickmatch or fast fuse between each motor for when I want a rapid ripple-firing. Some kind of Sabot system is also an option.

I'm itching to get back into my workshop now, my next priorities are:

1. Stabilise the fuel, slow it down, to make it reliable and ideally produce darker smoke.
2. Test a few nozzle designs to see how I can best induce the spin - I plan to do it primarily the way Microtek has described.
3. Finalise my rocket tooling and have it made up in metal
4. When I have reliable rockets, I'll be building my launcher and posting the results <img border="0" title="" alt="[Wink]" src="wink.gif" />

[shooter3]

When a motor burns it creats a vortex inside the motor. It can spin so fast that it will centrifuge the gases to the outside of the motor ID, and outside of the nozzle OD. The motor blows up.

The ASROC(anti-submarine rocket) has a series (12 I think) of nozzles aranged in a circle just inside the casing diameter. They are slightly cocked to compensate for the induced torsion.

How about trying the same, but put the nozzles straight, so as to use the torque to spin the rocket? Use very fast fuel for superfast acceleration.

The asroc goes off so fast you can't even see it. Just a big BOOM and it's gone. I beieve the sprint used the same arangment.

[xoo1246]

Remove

<small>[ December 20, 2002, 06:57 AM: Message edited by: xoo1246 ]</small>

[Arkangel]

Xoo, early in the thread we discussed something similar, but using plastic cut from soda bottles for the fins. Is the Al you're using very springy? I guess any fins would provide a degree of stability, although I would prefer them to be canted to add to spin as well. That itself makes them more difficult to construct, and to attach to the motor body. We also discussed "normal" fins, but with a sabot made from water pipe insulation foam.

My holy grail continues to be the fully spin stabilised rocket :D

[Sparky]

You mentioned wanting a black smoke from the fuel. It seems to me that when you try to do fancy stuff to a propellant you sacrifice some performance. Instead of changing the composition, put a smoke composition layer in the rocket. Say right after you ram the nozzle you ram in some smoke composition instead of rocket composition. This makes the core smaller, but I think it would be much more effective than trying to change the propellant formula.

[static_firefly]

I think that the germans during there rocket developments of WWII developed finless rockets that dragged the explosive behind them, althoe i dont think thats too good an idea for someone at home to try and reporduce as placing an explosive cargo behind the plume sounfs just a tad scary. I think the rockets they tryed went straight but slowly started to pull up and fly vertical or so i would think.

Anyway that idea that someone earler mentioned about the spinning caused by the direction of the nossle, i might try some thing like that say instead of having one hole have six smaller ones pointing down and to the side.....I might try that now.

[Flake2m]

Firefly i know what you are talking about to a certain extent. The propulsion system you are describing has been used before. A rocket engine is placed on top of the payload. This system was used in the pioneering days before the space shuttle, it was called the "escape rocket".
That system was used when it was easier to fit a propulsion system ontop because of space etc. It was also used when a different system was required to be kept seperate from the rest.

You could mount a rocket engine at the front of the missile, but it would quite difficult to control and balance, unless it is just ment to go up. The other problem with this sytem, it that the area below the engines would have to be heavily shielded from the heat, so it would not be a good idea if you planning to use AP as the warhead.

I have an idea though of how it could be implemented into an anti-tank system though. The payload could contain a large shaped charge below the engines and guidence systems. The rocket is fired from the ground at a high trajectory, once it is at a suitable alttitude the infrared tracking systems guide the missile to the target. The shaped charge then detonates ontop of the tank.

I do not know how accurate or stable a rocket of this design would be like. The physics would be quite different.

<small>[ February 26, 2003, 07:48 PM: Message edited by: Flake2m ]</small>

[static_firefly]

Yeah you know what i am talking about. When the germans were inventing the "neblerwerfur" (sp) i they tryed that.

Just before i tryed the nossel idea i had where i had 4 small holes pointing down and to the side so it would spin. It traveled straight for about 2meters (with a lovley spinning sound) then exploded. Im going to try another one probably monday where i will engrave a nazi looking set of groves into the bottom then put a cap on with a hole in the center so hopefully itl spin and not exploded. Il give this a shot monday and might try filming.

[nbk2000]

Maybe this will help you out.

<img src="http://www.adrax.com/watsons/g009.jpg" alt=" - " />

[static_firefly]

Ok i had some success. i lit the rocket from a small tube about 1foot long. The tube was pointing along the ground because i was next to a major road and didnt want people to see (my normal grounds are tinder dry). The rocket shot out of the tube, did a loop then continued straight along the ground until it smacked into a tree. After the loop it traveled quite nice (around 50m), il build a few more and fire them from an ovel verticel. And this time i will tape them.

[kingspaz]

that your shotgun dildo nbk :D
does it provide its own thrust once clear of the gun? if so then the fins would have to be made of a high melting point metal. high melting point = hard to shap = out of most members reach :(
thats a pretty interesting idea though!
you know the rocket nozzles on the space shuttle? maybe if one of those was used instead of the traditional built in nozzles then slits could be cut into it and the edges twisted slightly to provide spin.

<small>[ December 16, 2002, 05:14 PM: Message edited by: kingspaz ]</small>

[Anthony]

I'm guessing that thing gives thrust, and the fins are almost definitely aluminium. As long as the burn wasn't excessively long, the find would probably be relatively undamaged, due to their thermal mass.

[nbk2000]

Actually, it's a Flight-Rite barricade penetrating tear gas cartridge. It's fired from a 37mm launcher and is not rocket propelled.

Yes, the fins are aluminum, but you'd make yours out of sheet steel. And as long as the fins didn't melt off, they'd do the job, even if they get a little slagged. <img border="0" title="" alt="[Wink]" src="wink.gif" />

<small>[ December 16, 2002, 10:36 PM: Message edited by: nbk2000 ]</small>

[Arkangel]

Ok, while you're chatting away about plaster of paris in the Flash Powder thread, I have a question. It's really about an idea of how to mass produce nozzles.

Forget the details of how I'd make the moulds, but I have in mind a mould, a bit like one of those rubber ice cube trays, for mass producing cast nozzles. Ideally, these nozzles would be cast, set and then drilled on my workbench before being epoxied into the rocket body. It would be much easier to work on a nozzle before it was in the motor I reckon.

Anyway, you're all chatting in the flash powder thread about using Plaster of Paris as part of a comp. However, as the material for pre-casting the nozzles, is it going to burn, or will it withstand the heat and pressure????

[DarkAngel]

I made some fontains and used plaster for there nozzles.
There holes slightly enlarge after the fountains had burned.
I directly casted them in the cardboard tubes and never had any experiences that they where blown out, Afcourse this could be diverent if you would ram/epoxy them into a tube later.

<small>[ December 21, 2002, 09:15 PM: Message edited by: DarkAngel ]</small>

[Arkangel]

Cool, that's pretty much what I thought would happen. I'm interested in how you cast them, since it did occur to me to do them in place, once I'd rammed the fuel grain. If you cast them with your comp in-situ, how did you top the moiisture in the plaster from affecting your composition?(I had in mind a small disk of very thin plastic glued in place, which is then pierced when you drill through the plug for the nozzles)

(If the nozzle is strong enough, and a close enough fit, I don't think you will have any trouble at all with them blowing out. In applications like that, epoxy is incredibly strong. I would be tempted to score the inside of the motor body though, to make sure it had good purchase)

[Mr Cool]

It might be better to protect the rocket's fuel with wax or vaseline rather than plastic discs, it'd be easier to get total coverage. With plastic discs water could easily flow round the sides.

[Eliteforum]

Mr Cool, could you not use a combination of both? :confused:

[Mr Cool]

You mean use plastic discs/disks (which is it? I can't decide!) and seal around the edges with wax/grease? Yeah, you could do that. I thought about it but decided that if it was me making them I'd rather just use one or the other to keep it simpler, and I reckon grease would be quicker and more effective than the plastic.

[nbk2000]

Why not cast the nozzle first, then ram the propellant in from the opposite end?

Or, ram the propellant into a cardboard cylinder that just fits into the rocket body, and seal with aluminum foil. Insert the propellant cartridge into the rocket, cast the nozzle, then pierce the foil seal. :)

<small>[ December 22, 2002, 12:34 PM: Message edited by: nbk2000 ]</small>

[Arkangel]

Ok, well a couple of comments on your comments so far.......

Mr Cool, I think that vaseline/grease would make a good barrier to the moisture in the PofP, but it would be tricky to get it sealing without contaminating the tube that you're then wanting the cast nozzle to adhere to.

NBK, I like the idea of a cartridge, like you suggest. (and a bit like Nakka describes casting fuel grains) One way of doing it would be to have a paper sleeve inside a metal tube the same size as your motor body. Then, ram the fuel grain inside that. Once you had it finished, you'd remove the coring mandrel and using the press, push your "cartridge" out, along with it's paper outer. That should then slip neatly inside your rocket body, once it's ready.

I'm still pretty keep on the idea of casting and drilling the nozzles outside the tube and epoxying them in place, though in time I'll probably try both methods.

Ok, now some stuff I've been doing today:

My main concern has been slowing the fuel down that I've made, since I've had a high ratio of CATO's with my 70/30 Sodium Chlorate and sugar. It's probably a crappy fuel, but hey....it's what I have, and the same principles apply to others as well.

So, I tried 2 additives, vaseline and charcoal. Vaseline was interesting, since it was interesting to mix, and I made a quite pleasing dough with it. I added 25g of vaseline to 75g of my previous mix, and tried to keep it warm and pliable. I'd pre rammed my nozzle, and put globs of the paste into the motor. Ramming it was a nightmare though, as my tooling is quite precise, and I was having all sorts of snags with vacuum/pressure caused in the tube. Also, I'd clearly got air bubbles in the fuel, as "ramming" it felt like riding on a space hopper. This first mix was too slow, and the rocket fell off the launch stand and fizzled away. :rolleyes:

I tried other mixes of vaseline, and continued to have the same manufacturung difficulties, so will bin that idea for now. I recall somewhere somebody writing about making small balls of this type of comp and dropping them in - that might reduce the problem I had with air in the grain. I might at some point try a mix of just vaseline and oxidiser, and see if it's castable. I'm not optimistic though. :(

So, then I started adding charcoal to my comp, and I was getting much more promising results with that. Again, with 75g of original comp, and 25g of charcoal, I got a workable fuel. The main thing I think I've hit on, is that the tooling I have makes the nozzle too narrow. I read (after I'd had it made) that the nozzle should be about a third of the diameter of the tube, and my tooling made it about a quarter the size, maybe a tad less. So, on my later testing today, I used my dremel to widen some of the nozzles, and I found that those with a larger nozzle took a bit longer to leave the pad, but went for their full burn. Those that had the original nozzle took off ok, but then cato'd about 20 feet into the air. So, I'm pretty sure my nozzles need revision. I'll do a bit more testing with the same fuel and different nozzle sizes, then have the tooling modified.

Since not enough stuff had gone into the air tonight, I stuck a couple of Estes "C" motors into cigar tubes with some flash, taped them onto split canes and set them off while I sat on the back porch, smoking cigars and drinking beer with my mum. I have to let her neigbours properly know that I'm visiting you see <img border="0" title="" alt="[Wink]" src="wink.gif" />

Anyway, I'll keep you posted as I go on :)

[Mr Cool]

Have you tried polyester resin with potassium or sodium chlorate? A bit of charcoal will make it easier to ignite. This would make mass-production easy, you could mould fuel grains, end plugs and nozzles dozens at a time, and then just assemble everything with epoxy. With a free standing, free burning fuel grain I think you would have good results.

[DarkAngel]

When I made my fountains I first filled one part of the tube with plaster,after it dried a hole whas drilled in.Than a small piece of toilet paper whas inserted through the hole (to prevent leaking) and the composition whas rammed in.On top of the compostion I placed another piece of paper it whas rammed to make a good fit and on top of that a final layer of plaster whas casted.
This didn't gave any moisture problems.

<small>[ December 23, 2002, 05:33 PM: Message edited by: DarkAngel ]</small>

[Arkangel]

Mr Cool, have not tried it, but I was asking about it in another thread around here somewhere. If you have any ratio's that would be great, as I have access to polyester resin in vast quantities :D

I've had a look for them elsewhere, but any tips on that would be appreciated.

[Mr Cool]

I don't have any ratios really, but you could try a 65:35 mixture and experiment from there if necessary. As far as I can recall I've never tried it in a rocket, but I see no reason why it wouldn't work, either as a simple cylindrical grain, or tubular, or even broken up like gravel, depending on what its burn rate is like.
You'll probably need a very good igniter to get it started well though.

I'm going to try it out now...

(Continue the discussion of epoxy/polyester fuels in the appropriate topic; let's try to aim this one back on course.)

<small>[ December 24, 2002, 08:00 AM: Message edited by: Mr Cool ]</small>

[Arkangel]

Ok, well I have a bit more information after today's testing.

Casting nozzles in-situ is not likely to work so well, because of shrinkage when the plaster dries. (Darkangel, how wide were your fountains? There seems to be a lot of shrinkage on my 1" tube) I fairly sure of this because of the results of another idea I'm trying at the moment.

I REALLY like the idea of a pre-cast plug, drilled with nozzles before being glued into the motor with epoxy. I may end up making an icecream style rubber tray for it, but today I decided to use some of the 1" cardboard tubes I have as moulds. I currently have one filled up with plaster of paris, drying on a very hot radiator overnight. Once it's dry, I'll cut away the cardboard, and should be left with a 7" by 1" plug of hard plaster of paris. I'll then get that on the bandsaw and cut it into 1" lengths. These I can then drill at my leisure, with various nozzles for testing, before glueing them into my motor bodies.

This method has many advantages, but one which occurs to me as I'm writing, is that assuming there is a 1mm gap between the grain and the plug, there will be immediate pressure to EACH nozzle, however I ignite it. As opposed to a grain butted up to the nozzle, where it will have to burn through a fair way before you get thrust from each nozzle - unless you have an ignitor in each.

The main advantage of this method is the mass production potential. If you cast a 10" section of tube, that's nozzles for 9 or 10 engines. Also, instead of cutting the tubes, if you greased the interiors before casting, you might be able to push the casting out and re-use the tube. I've just taken delivery of 50 x 4' lengths of 1" id tube, so I'm not so worried at the moment, but it doesn't hurt to get into good working practices. <img border="0" title="" alt="[Wink]" src="wink.gif" />

I seem to have a reasonable speed fuel at the moment, and I tested a couple of 1" motors tonight. The tooling I've made up definitely makes the nozzles too small, as I've discovered by testing the same fuel with a nozzle as is, then a motor in which I've reamed out the nozzle to 1/3". The first cato'd, the second was fine. It won't matter for my spin stabilised babies, but I'll get the tooling re-made for general purpose rockets.

I think I need to do my testing in a less populated are now. These motors are quite hefty prior to launch. That's not so much of a problem if they go straight up, as burnt out they are light. The last one tonight was a worry though, it took off quite slowly (not ignited at the top of the core, and chuffing noticeably), and went at about 45 degrees, before heading back to earth somewhere the other side of the playing fields behind the house - still under power <img border="0" title="" alt="[Eek!]" src="eek.gif" /> I reckon part of that is that I'm using split canes that are neiter long enough, nor rigid enough to get them up to speed and directionally stable - a lesson learned for my launch system - the tubes will have to be at least 3' long

One of the other things I need to do soon is find a metal sleeve to go round my motors to stop them splitting when I ram or press them. Once I have that, my father has a hydraulic press, and it's off up to his workshop to get some nice, solid, consistent grains. :)

Edit: In the stinger instructions, they suggest using a few drops of sodium silicate solution to help make the vent hole more impervious to erosion. I wonder if there is anything that could be used to perform a similar task with the plaster of paris? (Darkangel you mentioned there was some erosion) Maybe that's nothing to worry about.

<small>[ December 25, 2002, 08:46 PM: Message edited by: Arkangel ]</small>

[DarkAngel]

I had that same problem too ones, The trick is to use the right amount of water to prevent shrinkage.But be aware that you need to handle fast otherwise your left with a rock hard substance.

[Arkangel]

I broke my plaster core out and chopped it into 1" sections. I tried drilling them, and was reasonably successful, considering it was done without a jig, or accurate measurement. (By skeg of ee, and rake of 'gob, as they say where I come from)

I used a 2mm drill to make the centre and (angled) side holes, and then a conical dremel reaming bit to enlarge the main vent. In fact, using this tool from the outside AND inside of the plug, you could make a quite passable venturi.

The main problem I had with this casting method was the number of voids I found when I was cutting the sections and drilling them.I think this means that I need to take a lot more care when loading the tubes with wet plaster. There seemed to be a void caused by shrinkage that ran most of the length of the casting, and as you mention Darkangel, I'll have to try and reduce the amount of water I use to eliminate that.

Of the possible 7 from that casting, I had a passable 3 nozzle plugs. I was going to try them out, with a bit of epoxy reinforcement. I had an unfortunate accident though, which I'll chat about elsewhere, and I didn't have a chance. <img border="0" title="" alt="[Frown]" src="frown.gif" />

[Arkangel]

It's been a while since I've had a chance to do anything, but when I was last at home I popped into a model shop and found something called "Air Clay", by Humbrol. Basically it's an air drying form of clay, "reinforced with nylon fibres for extra strength". I used a dowel to pack a blob of the clay down into a rocket tube that I'd pressed against a smooth surface.

I let it dry in the tube, then as I suspected, it was reasonably simple to tap it out, since it had shrunk a little.

I did the same thing a few times today, but didn't wait for it to dry before pushing them out - not so neat, but a lot faster. Anyway, I now have a load of very solid nozzle plugs, that will almost certainly be free from voids when I drill the nozzles.

My plan is to create a drilling jig into which to pop the plugs, and then each will be drilled consistently. I'll then epoxy them into the rocket body when I'm done pressing the fuel. I'm going to just try a couple of motors with a normal hole first, to see if the epoxy can hold the pressure.

I've taken some pictures, but don't have a digital camera. I'll post them when I get them developed.

[Tuatara]

Go here: <a href="http://www.space-rockets.com/Cptechno.html" target="_blank">CP Technologies</a>
Buy the book! It has everything you need to know about making your own rockets and engines, including software. Propellant formulations, aerodynamics of rockets, thermal calcs, structural calcs, propellant testing and characterisation, nozzle materials / design / construction.

Its even got some readymade designs all laid out for you to copy.

Question : do you know what the burn rate coefficient of your propellant is? If not, how can you possibly design an engine that wont self-destruct?

Incidentally, I'm in no way affiliated with CP Technologies, even though this is the second time I've pointed people to the site. I just really, really, like the book.

[Arkangel]

Some great pictures on that site Tuatara!

I don't doubt that it's a great book, and the q&a seems quite amiable. But here's the question, does it discuss finless spin stabilised rockets? If so, any chance you could summarise it for us? If not, then it's not really relevant. There's a lot of stuff on the net, like Richard Nakka's pages that discusses similar stuff to the CP Technologies book. Those rockets are an order of magnitude higher in performance than what I'm looking to achieve.

Essentially, in this thread I'm looking for comments and ideas on a mini-MLRS. A project in which I want to make mass produced, cheap, simple rockets without fins or a stick that I can fire from a tube. I also want them to explode at the far end (don't suppose they cover that?) You know the book, is all of that in there?
</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">quote:</font><hr /><font size="2" face="Verdana, Arial, Helvetica"> Question : do you know what the burn rate coefficient of your propellant is? If not, how can you possibly design an engine that wont self-destruct?
</font><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">The same way that people generally do it, keep testing different "designs" for the characteristics you want. Also, when you have a design you're happy with, keep testing fuel ratios until you get consistent results without the motor exploding.

I know it's not especially scientific, and that's anachronistic in a field that should be, but it's not that hard to find motor/fuel combinations which work reasonably well. Sure, the motor is not at maximum conceivable power 100% of the time, but it will do for me.

How about you up the book to the ftp <img border="0" title="" alt="[Wink]" src="wink.gif" />

[vulture]

</font><blockquote><font size="1" face="Verdana, Arial, Helvetica">quote:</font><hr /><font size="2" face="Verdana, Arial, Helvetica">Question : do you know what the burn rate coefficient of your propellant is? If not, how can you possibly design an engine that wont self-destruct?
</font><hr /></blockquote><font size="2" face="Verdana, Arial, Helvetica">Calculating the burn rate coefficient for your fuels is extremely hard. Alot of thermodynamics like burn enthalpy, pressure differential, specific heat capacity of the fuel, etc come into that.
And you're nothing with a burn rate coefficient alone.
Your nozzle and burn chamber need to be adopted accordingly and then you go into gas/fluid dynamics.

[Anthony]

Then of course consistant and repeatable enough construction to make the measurements at all relevant!

[Tuatara]

My humble appologies if you all thought my last post was off topic :o
Having watched this thread shift into comments on nozzle contruction, coring and propellant packing I just wanted to direct folks to some solid info. The question was meant to be amiable, merely to point out there's a lot to building a rocket engine.

Vulture : burn rate coefficient is relativly easy to determine experimentally. And all the equations are out there for calculating nozzle parameters.

Anthony: repeatable construction is a given. Since arkangel is aiming for an 18 rocket barrage, it would be very sad if the third rocket blew up on ignition and destroyed the launcher. Spectacular , but sad :D .

So to atone for my sins how about this : you could try 'rifling' the nozzle to impart spin to the exhaust. The torque produced would spin rocket.

Also look into making the thing as aerodynamically stable as possible to reduce your spin requirement. This means having the centre of pressure aft of the centre of gravity. A simple test for static stabiliity: pivot the rocket at its balance point (Cg). Hold it side on to a breeze, if the nose turns into the wind the rocket should be stable in flight. Usually fins are used to move the Cp aft, but you could possibly add mass to the nose and move the Cg forward. If you can achieve this then a small amount of spin will ensure stability.

Nozzle materials : I've seen many references to something called Durhams Rock Hard Water Putty. I've no idea what this stuff is but it is very popular among rocket builders. Canvas phenolic and graphite are also used, but obviously are not mouldable and need to be machined to shape.

upload to FTP? I'll think about it - the book is not expensive and I kinda think the author deserves his money.

[kingspaz]

but you must realise the more you contribute to the ftp the faster you have access <img border="0" title="" alt="[Wink]" src="wink.gif" />

[gamin guru08]

Like others have said...if two nozzels are used and one is off center the tiniest but then the rocket would be unstable. Those PVC pipes made for spud guns seems like a really good idea. I think making the rocket shorter would make it more stable and plastic fins from coke bottles doesnt seem like a good idea, just seems like they wont be strong enough.

[Arkangel]

ALRIGHT!!!!!!!!!!!!

Made 3 rockets today, only one is totally relevant to this thread, since the first 2 had sticks.

All used the same fuel, with a 6mm core.

1. had a nozzle plug made of rammed, ball-milled kitty litter. For some reason it never achieved full power, and just managed to lift off before heading horizontally acoss next door's garden into the yard of the garage beyond :( .

2. Had a rammed fuel grain, but a 1" thick pre-cast nozzle plug made from the "air clay" I've described previously. That was drilled with a central nozzle, really just to see if it can cope with the pressure. That rocket took a second to develop power, but then lifted off fine. It cato'd about 50' up. I'm 99% sure that the nozzle failed because it wasn't adequately glued in - some of it was protruding cuz the grain was too close to the end of the tube. I actually thought it would happen. :rolleyes:

3. My nirvana, a spin stabilised model rocket!!! :D

Ok, for this one I made a rocket 4" long instead of 8, mainly for for speed. (my tooling has interchangeable coring mandrels) I also used one of my precast nozzles, but this time instead of a single central nozzle, I drilled two, both canted at opposing angles. I made a decent job of epoxying it in, although since this was just to prove the principle, I didn't spend long getting it totally accurate.

I ignited this one with some fast PIC shoved up one of the nozzles into the core. I launched it from a 2' bit of UPVC drain pipe, at a 45 degree angle. In fact, it behaved pretty much as I'd hoped. I'll try to use quickmatch next time to get the whole core lit immediately (it was chuffing as it launched). However, it soon got up to power, went out of the tube and swayed a bit, but you could see the thing turning. It had a bit of a corkscrew trajectory, since it clearly wasn't turning very fast, but if I make sure that future nozzles are accurately aligned, I don't think you'll notice very much, especially when I'm ripple firing 18 of them :D

I'm really pleased. It's clearly going to work, and now I've found a material that I'm happy with for the nozzles, I can look harder at a couple of design options AND ways to mass produce them. (The only nozzle variation I'm going to have is a main central nozzle, and 2 smaller side nozzles, but at quite an acute angle)

I have a huge supply of 1"id tube, so I plan to cut twenty or so 1" lengths, glue them together like a honeycomb, and then make batches of 20 nozzle plugs at a time. When I've decided on the nozzle design, I'll make up a drilling jig and I'll be sorted!

Bloody hell, I'd better start designing my launcher! :)

<small>[ February 21, 2003, 10:37 PM: Message edited by: Arkangel ]</small>

[gamin guru08]

Nice work on those rockets there. Are you using fuses to ignite them? I may have to experiment with those one day when I'm bored.

[Arkangel]

Ok, 2 more tests today, and both successful. They had the twin nozzle configuration, and worked a treat. One was only half the normal length and set off much more slowly - it rattled up the inside of the launch tube. However, you could clearly detect a spin. They shot out of the launcher dead straight.

I've done a couple more to test - one with the twin nozzle design, the other with 3 nozzles - 1 main and 2 smaller spinners These pictures are shit, when I have some decent ones I'll post them.
<img src="http://www.boomspeed.com/arkangel/2rockets2.jpg" alt=" - " />
(The twin is on the left, the triple is on the right)

I also made my honeycomb nozzle plug mould.
<img src="http://www.boomspeed.com/arkangel/Nozzleplugmould.jpg" alt=" - " />
With this I can make 20 nozzle plugs at a time. They take about 4 hours to dry, so I can have 40 plugs prepared in a day. I have yet to test a triple nozzle rocket, but I'm 90% set on the double:

1. It seems to work just fine

2. The construction is inherently stronger than the triple, AND simpler.

Now I just need to make a drilling jig to get my nozzles drilled accurately.

I've ignited them with a combination of slow PIC, connected to fast PIC shoved up the core. I will also be trying quickmatch shoved up the core too

<small>[ February 22, 2003, 08:02 PM: Message edited by: Arkangel ]</small>

[Mr Cool]

Sounds like you're making some very good progress with these things, next time I make a rocket I'll try it myself.
Two questions, sorry if they've been answered but I couldn't find them:

1) Did you decide on a suitable fuel in the end, or are you still experimenting?

2) Roughly what angle do the twin nozzles make with the vertical?

[Tuatara]

Have you considered electric ignition, or is that too complex for your app. I mention this because a sqib can be put deep inside the grain to achieve rapid ignition along the entire core. This approach is used with composite propellants, as they are somewhat harder to ignite

[Arkangel]

Gamin, I'm using plain fuse at the moment, (PIC), but the problem with this for any cored rocket is that it doesn't ignite the core from the top, and the flame front has to pass gradually up the core as the motor ignites. This produces a slower take-off, and is the cause of the "chuffing" noise you often hear. There are a couple of ways of dealing with this, and if you look hard at the piccie of the 2 rockets, you'll see that it has some green PIC, secured with red tape into some quickmatch, which is inserted into the nozzle. This is ok for single nozzles, as it is just blown straight back out, however, I'm worried about using it, or any other form of igniter that goes in from the nozzle. This is because debris (wire/paper/slag etc) might be blown back and clog one or both nozzles. This will result either in a very erratic flight, or worse, a CATO.

However I have a pretty cool idea in mind for igniting from the top of the core, one which will look more the part, and not have crap hanging out of the bottom. Basically, for the end plug at the top of the motor, I'll be using another of my precast plugs. This I'll drill, and epoxy in either a commercial electric squib (pricey) or something I've made myself. Either way, once it's been epoxied in place, the wires will be led out through the side of the motor, to be connected to the firing leads prior to loading into the launcher. When it's fired, the squib wires will just pull away from the shooting wire and the rocket's on it's way - with the core lit from top to bottom. (Chances are though, this will all be too much effort and I'll continue to light them with PIC or quickmatch linked from one nozzle to the next for my ripple firings:))

Mr Cool, I'm not set on the fuel, the "testing" I was doing was really to find a use for the Sodium Chlorate I had a few Kg's of. I now have a lot less of that, so I'm probably going to use Saltpetre as an oxidiser and sugar or charcoal as fuel. Suggestions welcome :)

Also, the nozzles are at an angle of something like 45 degrees at the moment, but that was just cuz I was excited and wanted to see if they would actually spin. My next trials are to see what angle provides the most thrust, but still with adequate spin - I'll let you know.

Tuatara, the electric squibs I have are unsuitable for this app not because of complexity, but because they are made of substantial plastic, and would block the nozzle/s when fired UNLESS they were set into the top of the motor as I've described above. They could be just stuck in a nozzle, but the flame wouldn't reach to the top of the core. In this respect I'd be better off with a length of quickmatch pushed an inch or so up the core. One thing about this is that quickmatch tends to produce the fastest longest flame when it's loose enough for the flame to travel up it. If you pinch or roll it, it acts more like time fuse and slows down. I'll be trying some fast PIC inserted all the way up the core as well. It might take a second or two to burn all the way up, but it IS going to do it, and chuffing should only occur for a second.

Oh, and before anyone advises me to fill the core with FFFF black powder - I don't have any....donations gratefully accepted:)

[Anthony]

This is going to sound pretty obvious, but just in case you haven't thought of it...

Take some of your quickmatch, remove the blackmatch and scrape/crack the BP coating off over a sheet of newspaper and sprinkle some into the core of the motor before gluing the nozzle in.

Failing that, get some Estes motors from a hobby shop, cut them open and powder the grain and use in the same way. It's pretty fast burning stuff when finely divided and is what I used for KNO3/sucrose motors. An advantage of those motors was that the prime stuck to the fuel, coating the core nicely.

[Arkangel]

Hey, and I've just realised I'm being a plank here......

In quickmatch, the flame travels so fast because it's loosely contained inside the paper sleeve. (I have plastic coated quickmatch)

Burnt on it's own, it will be just like slow fuse, but if I were to get a piece and strip off the paper almost as long as the core, then insert it all the way up, the core of my rocket should work the same as the quickmatch sleeve, and get flame to the top in a fraction of a second!

Anthony, thanks for the thought, I've load of Estes motors, and am normally loathe to use them for anything other than firing, but you can't make an omelette etc............... :)

[Mr Cool]

Hehe, crushing up Estes motors to prime your rocket reminds me of a solar powered torch I once saw... :)
Yeah, go with KNO3/sucrose. This can require quite a hot ingiter, since the inside of the core will be totally smooth (no sticky-out bits to catch fire), and also the sugar has to melt before anything will happen. Quickmatch should cope though. Replacing some of the sugar with charcoal will make it easier to ignite, as it does with most mixtures - yesterday while trying to get MHN mixtures to DDT, just for a laugh I made a rocket with MHN and 10% charcoal in a little cardboard tube. MHN is normally hard to get to burn in a controlled manner on its own, but with 10% charcoal it burns like SP - quickly and totally. The damn thing flew as well!

[Arkangel]

Another very successful test yesterday :D , 2 in fact.

The first, a static test of a triple nozzle. I was using a piece of quickmatch with the sleeve removed over the section inserted into the rocket core. The motor lit flawlessly, and burnt without chuffing, which convinces me that quickmatch is the way to light them as described. The other thing I noticed was that the main nozzle was clean afterwards, but the spin nozzles had an accretion in them, and this would have been a problem in flight - I don't think I'd achieve sufficient rotation with this design.

Next I fired a twin nozzle variant from a 2 foot tube. Used fast PIC instead of quickmatch, so it lit relatively slowly and chuffed. It took off gingerly, and corkscrewed a little for the first 100 yards, but then seemed to straighten up and flew as straight as a die. Did the test at dusk and it was well impressive to see this little flame streaking off into the sky.

In the nose of the motor I'd put one of those orange smoke pellets that Anthony discovered, so I legged it off to try and find it whilst there was still some smoke coming out. I wish I'd painted the motor a bright colour, as it would have been easier to find, but in the end, aided by the smoke, I did find it, about 500 metres away from the launch tube.

This test went almost exactly as I'd hoped, and lit with quickmatch I reckon these will be easy to launch in a ripple firing of as many tubes as I build into my launcher.

Next testing will be a new saltpetre/sugar/charcoal fuel, and different angles on the twin nozzles. I'm also going to start constructing my launcher. It will be modular, and I'll start with 12 tubes. Pictures of all will naturally be posted when available. <img border="0" title="" alt="[Wink]" src="wink.gif" />

<small>[ March 18, 2003, 11:30 AM: Message edited by: Arkangel ]</small>

[Arkangel]

A couple of extra bits of thinking I'm doing............

1. The rockets always seem to take a second or two to get up to pressure and lift off. To make them more explosive and accelerate faster with more spin quickly, I was thinking of using a small plug of silicone rubber in both the nozzles. This would contain the flame long enough to ignite the whole core and build up some pressure before launch.

Any thoughts?

2. Nozzle size, I understand that a fair ratio for nozzle size is 1/3 the diameter of the motor body. I'm therefore assuming that each of my twin nozzles should be 1/6 the diameter......does this stand up to logic? I think so anyway, but please comment. (I can't find a pi symbol on my keyboard!)

HOWEVER, the core is smaller at launch, so relative pressure is lower. Nozzle erosion does take place, so the next thing I'm going to measure is how much bigger the nozzles are after a static test, and see if I can make them smaller initially and not suffer cato - since the relative size will stay the same throught the burn.

[Anthony]

(1/6th dia x 2) would not be the same as 1 x 1/3rd dia, they'd only be about half as large You need to work out the area.

A pressure plug is a good idea and often employed in larger motors. Not only does it give the core longer to ignite, the sudden pressure release when the disc burst give a nice instant boost of acceleration.

[Tuatara]

Regarding point 1: Could be your core diameter is a bit small - there may not be enough initial burn area to provide the mass flow needed to pressurize the engine and generate thrust.

Regarding point 2: Throat area should be based on the burn surface area of your propellant grain - obviously a long core is going to produce a higher mass flow rate and therefore need a larger nozzle hole - regardless of the diameter of the motor. From the CP technologies book :-

Throat Area = (mass flowrate)x C* / ((chamber pressure) x 32.2)

Area in square inches, mass flow in lb/sec, C* is the characteristic velocity of the propellant in ft/sec, pressure in psi, 32.2 seems to be a magic number!

From Propep I get C* values around 3800 for NaClO₃ / sugar (70/30),
and a chamber temp of about 4000F at 100psi. Propep is a bit of free software available readily around the Net - quite useful for inital engine design work.

Also, if your core area is less than 4 times the area of the nozzle you can expect 'Erosive burning augmentation'. Basically the speed of the gas passing over the surface of your grain increases the burn rate. Not necessarily a bad thing, but worth being aware of.

Edit: fixed brackets on eqn!!

<small>[ March 18, 2003, 08:49 PM: Message edited by: Tuatara ]</small>

[Arkangel]

I've not had a play yet, but it does look useful. Here's a link to <a href="http://lekstutis.com/Artie/PEP/Index.html" target="_blank">PROPEP/GuiPEP</a>

[Arkangel]

OK, well I've been making progress, and now I'm more or less set on the design of the rocket I'm going to use:

1" tube, with the fuel grain rammed, and then a pre-drilled nozzle plug epoxied in place. There are two nozzles, at an angle of approximately 60 degrees from the horizonal. (This may change, with prolonged testing)

The rockets are initiated with commercial quickmatch that has had the sleeve removed on the part which is inserted in one nozzle right up the motor core. They light perfectly this way, with no chuffing, and always launch within half a second of initiation.

The fuel I'm set on is saltpetre, sugar and charcoal 65/30/5. The charcoal is there to aid ignition, but more importantly because it's a fantastic way of checking that the fuel is well mixed. I considered casting it, but had limited success, and for now I'll just be ramming or pressing it.

After ramming the fuel grain, I've dropped in a plumbers smoke cartridge, with the open end touching the grain. I've sprinkled a few mm of ball-milled kitty litter around it, then filled it to the top either side with hot glue. I've drilled a small hole into the closed end of the smoke cartridge, and hot-glued a length of PIC in, which takes fire from the smoke (delay) cartridge and ignites the flash payload.

For the exploding "payload" I'm using a 1-1/2" section of the same tube as the motor body, which I've hotglued and then taped onto the rocket body. That extension section is filled with flash and then plugged with a "reject" nozzle plug (about half of them at the moment have flaws).

I tested one yesterday (without payload) and 3 today (with). Yesterday it was fired in quite windy conditions, at an angle of about 60 degrees above the horizon. The rocket seemed to go almost vertically, and although there was a clear corkscrew track, it span so fast that there was an audible hum - like a gyroscope spinning up!!!!!

Today, the rockets were heavier - the maximum weight I'll be using. 1st I fired one on it's own, and it went ok, fell short because I fired it at too high an angle - only went 150m. Also, the delay was too long, although I was pleased that the delay mechanism worked exactly as I'd hoped - to shorten the delay, I just need to drill deeper into the smoke. The rocket had a corkscrew track, maybe a metre in diameter. Increased nozzle accuracy, plus plugged nozzles to get increased pressure at launch should help this (plus WD40 - see below)

The next to I fired as a salvo. I'd got two launch tubes together, and the quickmatch from rocket #2 was inserted into the "spare"nozzle of #1. When fired, they launched almost simultaneously. For dramatic effect I'm going to have to introduce some kind of delay into the ripple firing, but that's easy enough.


Things I need to do now:

1. Get some pictures developed for you lot
2. Sort out my nozzle drilling jig
3. Get a press, or spend more time ramming - #2 cato'd after a second or so, possibly as I did it in a hurry
4. Lubricate the launch tubes with WD40 before firing,
5. Test rockets that have quickmatch sealed into both nozzles with silicone, one bit to fire, the other to take fire to the next rocket
6. Varnish the the rockets, to make them smoother, and more able to slide up the launch tubes
7. Build about fifty rockets, just to fuck about with and generally get the feel for how these things are going to work.

I would have done shitloads more at this project, but have been sorting my workshop out. Plus I had to make upwards of 60 shotshell boomers, and some larger boomers for a little "thang" I have coming up. NEXT time I make rockets, it will be a concerted effort to make sure I get this project workig properly.

Edit: And this morning I looked up the launch tubes, and noticed that there is a distinct spiral pattern of muck, up inside them. It looks just like the inside of a rifled barrel, and there are probably 2-3 full twists along the 1m tubes. I get the impression from that, that I've got TOO MUCH spin, and am losing performance because of it. They certainly have a distinct corkscrew smoke trail. Next tests are all going to be fulll weight, but with various nozzle angles, beginning with a very fine one.

[Arkangel]

It's been a while since I did much on this thread, however last weekend I did a bit of relevant rocketry. At the moment I'm mainly ramming the tubes with fuel 65/35/5 Saltpetre/Sugar/Charcoal that I'm happy with. I want a stock of these so that when I get my nozzle drilling jig sorted I can knock them up quickly. (so far I have 15 tubes with fuel rammed, another 8 with nozzles installed)

Anyway, I can't make any rockets without firing a few, so I ended up firing about 8, and have the following observations.

In an earlier thread, I discussed putting a "nozzle plug" of silicone in, to help the pressure build before launch. For most of these, I inserted the quickmatch (with sleeve removed for the part inside the core). I then made a plug of hotglue and bits of wooden spatula (stolen from Starbucks). This gave a noticeably more punchy launch.

I think I need to increase the diameter of my core. At present it's 6mm, however the nozzle/nozzles are larger than that, which leads to quite a slow launch. I'd like to deal with this by either increasing my core diameter (meaning less fuel, and possibly shorter range) or having an ablative lining to the nozzle (meaning the nozzle is initially smaller, therefore higher pressure initially, and the lining erodes as the motor increases in pressure), or having a more a more solidly fixed nozzle plug (so that it acts almost like a salute, but instead of the tube bursting, the plug/s blow out, giving an instant kick)

For those who are new to this, the problem with a simple cored rocket is that as the core burns, the burning surface area, and therefore pressure increase manyfold. As such, a simple nozzle is a compromise, giving poor thrust initially, and risking an explosion toward the end of the burn. Obviously, there are solutions such as complex core shapes, or a bates grain (burning from the inside AND outside), but what I've always been trying to achieve in this thread is a very cheap, easy to produce rocket. (to fire at my dad's house, since he's a cunt (long story:( )

I tested the hotglue plug last weekend and it seems to work ok, however, I ony tested it on single nozzles. On a twin (spin stabilised jobbie) there will be much increased adhesion (a plug in 2 nozzles rather than just one - don't make me do the sums) and I think this may help a great deal in my spin stabilised models.

Finally, if anyone has suggestions for the ablative nozzle lining I would be really grateful - bearing in mind I'm using a preformed/drilled Airclay nozzle. Wax, no (easy to put in there, but would melt too quick) a hotglue plug with a hole drilled through, maybe, (might work, and quite easy to do) a layer or two of epoxy, maybe (harder to apply, but might be more resistant to efflux)

[Guerilla]

I dont know if this is a doomed idea from the beginning, but how about increasing the initial thrust by means of a temporary nozzle (smaller of course) placed under the primary one, which would eventually blow out but leave the primary nozzle to take care of the rest of the flight? Naturally there should be a decent gap between the nozzles, forming the chamber which the gas can occupy and where over pressure can arise.. attaching the temp nozzle lightly enough is a whole another story as the chamber explosions and faulty nozzle spit outs can very well knock the rocket from its "course". - I really dont know would this be a working solution?

I havent made any core-burners for a while now though. In past times I have experimented with bigger end-burners, using catalysed candy fuel and 45mm ID PVC pipe (insulated with paper). The previous one had a grossweight of 480g and 208g of fuel, it was a pretty loud Wooossh :p I was expecting it to go into heights but then in an altitude of couple ten meters apparently the heat ate through the paper insulation and it changed into a flying fireball. It crashed into a lake. :( I will make more of them with thicker insulation layers.

I have planned the dimensions for a bates grain rocket using the same tube, the rockets lenght will be around 25-30cm. The fuel weight probably 400-500g. That will be a killer, if it wont CATO ;)
I hope I will get some pictures of them..

[Arkangel]

I used to work with Surface to Air Missiles (Rapier), and they have a boost segment to the motor core, with a sustain segment outside it, like concentric cylinders.

This might be something to consider - first of all ram the main fuel, leaving a much larger core. Then have a preformed "cartridge the same size as the core (with a core of it's own) that you insert. That way you'd get a good boost when the nozzle is relatively large, and by the time you the nozzle was on the small side, you'd be running on the slower fuel.

Anyone ever tried anything like this?

Guerilla it's an idea certainly, but I imagine it would be hard to: a. keep it consistent, and b: use this with the twin nozzle spin stabilised design

[Tuatara]

Your simplest fix would be to increase your core size, as you said. If launch is slow then that fuel is probably being wasted on the launch pad anyway, so the impact on range would be minimal.
You could always make the engine longer, if you want to keep the fuel quantity.

[Arkangel]

I agree Tuatara.

My last test before enlarging the core will be to have some well fixed in nozzle plugs to see if I can get a bit of impulse from them blowing out. If that don't work I'm reworking my tooling:(

[vulture]

Have you ever considered coating the barrel with teflon grease? This will greatly reduce friction but will probably kill the necessary spin too i'm afraid.

I've been thinking what if you would make your barrels rotate? Spin em up before launch and the rocket maintains the spin for a while leaving the barrel.

[Arkangel]

The barrels are a little under a metre long, and on all my launches so far, there's been a trail of dirt on the insides, just like a rifle barrel. They are spinning as they leave, but along the lines of what you've mentioned, I plan to spray some WD40 or similar lubricant down each barrel before I fire them. Grease of any kind will be a bit thick I think.

My barrels are all going to be fixed firmly together. The idea you mention about getting the barrel to rotate is better fixed by the lugs and rifling mentioned by NBK on page one, as with the MLRS. I think these babies will be spinning enough as it is, I just have to find the optimum nozzle angle for the full weight rocket - as much thrust as possible, with sufficient twist for stability.

[Tuatara]

I'd get some silicone spray, not WD-40. Most of those light oils dry out and become sticky after a while. In fact one place I worked had this insanely slippery patch on the floor where someone spilt some silicone lube - they had to fix it by coating it with belt dressing, went from slick to sticky in one short step

[Arkangel]

Silicone it will be Tuatara:)

I test fired a few recently, (out of a mock up SAM7 that I'd made actually!) and I'm not sure exactly what went wrong, but I found them VERY unstable. My suspicion is that it was caused by the hotglue I'd stuck the quickmatch in with blocking one nozzle and I've decided not to use plugs at all. The hotglue plug works fine where there's a single nozzle, but with two, it's too unpredictable as to how it will behave. In future, the quickmatch will just be loosely inserted:mad:

AND the motors that I've stored for a while seem very prone to CATO's. (Although these are pretty cool as they are like mini-Columbia shuttle disasters) I'd have thought they would have absorbed moisture and got LESS prone. Any ideas why?

[Tuatara]

I would think your CATOs are caused by cracks in the propellant grain. The cracks could be due to thermal cycling in storage, or maybe dimesional changes due to water absorption. Do either of these seem possible?

[nbk2000]

During a recent google search on gyrojets, I found a site I've never seen before, www.deathwind.com .

Seems someone is trying to recreate the gyrojet. :)

'Course, they're going all about it all wrong. They're still trying to use gyroscopic stabilization through canted vents.

Tsk, tsk, tsk. Obviously inferior to my hybrid gun/gyrojet concept, the Gy2. :D

Interesting how they're using .50BMG full metal jackets as rocket casings. Might be usuable for improvisation.

[Yafmot]

The Gyorojet gun was an obvious flop, but still fun to shoot. At very close ranges, it was pretty much useless, the projectile just bouncing off the bad guy (probably just tickled). Give the thing a chance to accelerrate, and look out. THEN the thing could HIT.

Many years ago, a friend of mine worked at Mather AFB on safety/survival gear for the B-52s out on the Alert Pad. Among other things, he armed the egress systems (ejection seats), rerigged the parachutes, and packed and inventoried the personal survival gear.

Among the various goodies he gave me was a neat little aerial flare kit with a launcher about the size and shape of a Mini-Mag flashlight. No it was NOT a penguin gun. I've had one of those, too, and they work by screwing in a cartridge which functions as both a storage device and a barrel, with a shotgun primer at the back. And it kicks like a MOTHERFUCKER!

On the other hand, the kit had a half dozen or so red cylinders about 3/8" diameter, and about 3" long. The body was deep drawn Aluminum, and at the ass end was a roll crimped, bronze or red brass plug with two canted gas ports and a primer in the middle. To launch, the load was inserted, primer end first, into a springlike collet. There was a spring loaded striker with a button protruding through a slot in the launcher body. The button was pulled back to the rear of the slot, and then pushed sideways into a detent notch. When the device is aimed in the desired direction, the button is pushed out of the detent notch, allowing the striker to fly forward and hit the primer.The launch is NOTHING like a penguin gun which, in addition to the disagreeable recoil, is flat guaranteed to make your ears ring hard.

On the other hand, the little rocket is as quiet as any squirrel fart. Beside the slight "chink" of the striker, all that is audible is a quick, faint "Pfftht." A few seconds later, at a truly impressive altitude, a bright red point of light would appear and remain for a good 15 seconds or so.

On the launcher, there are roll marks reading "MBA ASSOCIATES. SAN RAMON, CA. USA". Yep, it's a GyroJet. I was accquainted, for a while, with an engineering manager there and , in fact, made the short list to replace him when he moved to another position at another plant. He gave me the whole rundown on the flare system.

For starters, the thing will penetrate a 300 foot jungle canopy and still gain another 300' after that. Other colors included green, blue, white and the best, deepest yellow I've ever seen. NO SHIT! There are Pyros who would kill to get that formula, once they've seen it work. (Maybe I can get it.)

My B-52 friend also told me that, in Thailand, a bazillion of the things wound up on the black market. Apparently, the street gangs loved 'em. Sure, they had the same problems at very close ranges as the gun did, but fired from across the street the thing would penetrate quite nicely and then burn to completion in the belly of the poor bastard who took the round. 5,000 degrees F, right in the core of your pancreas. What a fucked up way to go!!!

I've got to figure out how to scrounge up another one of those!

[-=HeX=-]

Wow. That was interesting. I would indeed kill for any of those formulae, especially the blue and yellow. I dislike the sodium yellow. 600 feet altitude? I see great potential for that as a weapon, as did the gangs. I will later in the week try drilling canted ports in an estes engine to examine the effect it has.

I had heard somewhere here of a method of stabilizing an estes engine with a piece of pipe with holes it it here. Apparently it worked for horizontal firing. Does anyone remember it?

[rangegal]

Well I know a lot of you wish you could make nice flip out fins for your rockets, and I know some of you have tried. I myself tried using plastic sheet from those Mead spiral notebooks for the fins. It came a few feet out of the barrel and shot straight to the side and into the woods... thank God it didn't go in my direction. I haven't messed with that idea since. Anyway, for $35 you can buy a rocket kit from Aerocon that has a metal flip-out fin can. Apperently they salvaged them from surplus rocket flares. I can't wait to buy one! I won't however be using it for what you guys theorize about using it for. It's pretty cheap, but I still don't have that kind of money to burn, or... blow up :). But maybe it could be useful for reverse engineering a disposable version.

http://www.aeroconsystems.com/rockets/flippifin.htm

They even have a two stage version! A normal rocket goes up, burns out, and the flippifin rocket pops out of it and resumes flight!

[-=HeX=-]

Oooh I like! I imagine using them on the katashua battery... or on an improvised RPG of sorts. Does anyone know where I can find a diagram of a commercial 38mm flare? I believe they are rocket propelled. Because I need a diagram for a project I will be posting here. I intend to remove the flare material and replace it with an explosive. The flare material will then be used for stars.

The idea of this is to develop a easily used, rapidly reloaded, portable weapon which can engage vehicles with an explosive payload. What do you all think?