27 replies to this topic

[digger]

I have been working with a local WW2 re-enactment groups pyro guys to simulate RPG's (fired down a guide wire) we have used bp end burning rocket motors with Ti. To keep the thrust down they have had a relatively large nozzle (so they don't go to quickly down the wire). The Ti was included to increase daylight visibility. So far everyone has liked the effect.

However it is time to advance these devices a little and after a little discussion it has been decided that a good effect would be to have a fuel that produces a good jet of very bright white light (the longer the tail the better). After a bit of experimentation we have come up with the following as a possible fuel.

Barium Nitrate 60
Aluminium spherical (63 micron max) 20
Sulphur 10
Aluminium Dark Pyro 10
Boric acid +1

We have tested the fuel in an open tube (mildly pressed), it produces a good white flare with a moderate burn rate. It is proposed to mill the Sulphur, Barium Nitrate and Boric acid together and then mix in the aluminium powders. The proposed motor is to have an id of about an inch with and a total length of 100mm (core length and taper to be determined in testing). It is proposed to press this composition in a hydraulic press to around 10 tonnes per square inch.

Right so now for the questions does anyone see any problems with this formula, does it seem safe enough to press to form the motor grains?

[MDH]

So far I see none with the composition itself considering there is boric acid. But aren't you a little worried these rockets may explode?

[digger]

So far I see none with the composition itself considering there is boric acid. But aren't you a little worried these rockets may explode?

This is one of the issues I was concerned with. The initial fuel was basically a spherical aluminium powder / barium nitrate composition, but this was far too difficult to ignite to make a reliable fuel for on cue launching. Hence with a bit of experimentation the sulphur and pyro aluminium reduced energy required to ignite the fuel (I haven’t done the stoichiometry, but assume the comp is under oxidised). But as you mention it has a resemblance to flash type powder and this was my biggest concern when testing the different trial compositions (did not want accidentally make ground salutes).

The final test was with 20 grams lightly pressed in a 15mm ID open ended tube, the burn time was about 6 seconds. I suppose one question that needs to be resolved is will this or how much this compositions burn rate increases with pressure, also is it safe to press.

[dr thrust]

looks like flash to me , could you get rid of the sulphur( could be making the mix shock sensitive, mybe test a miligram amount with the anvil test) and up the pyro aluminium, ive been experimenting with manganese oxide ,spherical al as a rocket propellant and its a pain to light(magnesium ribbon does the job!) but with adding the right amount of pyro dark i can light it with visco

[BrightStar]

I'm not sure you're going to get a useful amount of thrust from this mix, though it will burn very hot and bright. It's essentially a white flare. I have several times tested similar mixes using 5:3:2 KNO3, S, Atomised Al.

1" ID is going to take a lot of comp and make for a very heavy driver. Do they need to be this big?

The sulfur is pretty much essential to get Atomised Al flares to ignite, though I'd question the need for Dark Al. I don't immediately see any problems with pressing (carefully) but you'll need to research this more. Bear in mind though that due to the metal content, a CATO would be very energetic....

Edited by BrightStar, 07 December 2007 - 09:10 PM.

[digger]

I'm not sure you're going to get a useful amount of thrust from this mix, though it will burn very hot and bright. It's essentially a white flare. I have several times tested similar mixes using 5:3:2 KNO3, S, Atomised Al.

1" ID is going to take a lot of comp and make for a very heavy driver. Do they need to be this big?

The sulfur is pretty much essential to get Atomised Al flares to ignite, though I'd question the need for Dark Al. I don't immediately see any problems with pressing (carefully) but you'll need to research this more. Bear in mind though that due to the metal content, a CATO would be very energetic....

I need to get around 300 grams of thrust, any more and they move to fast as they don't have to overcome gravity. So I hope with a bit of experimentation on nozzle and core sizes this should be possible.

The actual ID will be 21.3mm as I have already made a large selection of tooling for this size including quick release case supports, the total length will be no more than 100mm. (my bp rockets at this size can lift a 200gm shell with 1.3m 10mm square stick to a very respectable height).

The reason I put the Pyro aluminium in was because it seemed to make the mix easier to ignite whilst maintaining a high metal content, however I suppose I can try to increase Sulphur to exclude the Pyro ally (this would be a good thing to keep the cost of the drivers down).

looks like flash to me , could you get rid of the Sulphur( could be making the mix shock sensitive, maybe test a milligram amount with the anvil test) and up the pyro aluminium, Ive been experimenting with manganese oxide ,spherical AL as a rocket propellant and its a pain to light(magnesium ribbon does the job!) but with adding the right amount of pyro dark i can light it with visco

I have not done an anvil test before, however that may put my mind at a little more ease before I press a tube with 40gms in it. I assume that you are trying to use the manganese dioxide as a catalyst to speed burn rate?

[Arthur Brown]

I'd prefer to look in the lemaitreltd catalogue for ready made commercial line rockets.

http://www.lemaitrel...UKeyProduct=145

[pyrotrev]

I would have thought that if you're after something that looks like a pukka military rocket, a resin/oxidiser/Al powder mix would be best. If you use KNO3 rather that AP that should give a reduced burn rate, also a polyester resin will likely be slower than PU or resorcinol. Mmmmmm ..... might just try one myself!

[digger]

I'd prefer to look in the lemaitreltd catalogue for ready made commercial line rockets.

http://www.lemaitrel...UKeyProduct=145

Fair point, we may end up using something like this.

They are similar to what we have used before except we had a bigger tail. The problem is we are trying to re-create a military effect and would like to see if it is possible to get a more accurate looking effect that is very daylight visible.

With a bit of luck we should be getting hold of some land suitable for testing shortly (if the sale goes through we will start looking at required buildings, regulation testing etc)

[digger]

I would have thought that if you're after something that looks like a pukka military rocket, a resin/oxidiser/Al powder mix would be best. If you use KNO3 rather that AP that should give a reduced burn rate, also a polyester resin will likely be slower than PU or resorcinol. Mmmmmm ..... might just try one myself!

Yep that thought has crossed my mind and we may yet go down that route. The reason for going down the pressed route is we have the kit knock them up quickly for testing when we get to that point.

[pyrotrev]

Yep that thought has crossed my mind and we may yet go down that route. The reason for going down the pressed route is we have the kit knock them up quickly for testing when we get to that point.

Actually, with a nitrate oxidiser, magnesium would be better than aluminium, in fact it might be better full stop, since magnesium vaporises easily and will burn as a vapour in the tail of the flame. I just tried a KNO3/Red Gum/Mg mixture and it burns well with a big white flame, although a bit sparky since my Mg was only 50...60 mesh. With finer Mg I guess it would be much smoother, it might be necessary to replace some of the KNO3 with K perc to avoid dross build up?. The secret will be to under-oxidise the mixture a bit so that there's combustion happening in the exhaust gas tail, but still keeping the burning rate up high enough to give a high exhaust velocity: should be fun working on it!

Edited by pyrotrev, 08 December 2007 - 04:10 PM.

[icarus]

the safest low thrust rocket mix must be zinc and sulphur powder perfect for line run rockets or pigeons as they used to be called with lots of zinc oxide " smoke" as they fire. I often fire my rocket motors dowm my amateur radio aerial . alan yates propellant mix doesnt need pressing very hard and would be a good alternative starting point or kno3/sugar rockets a second tube with a vigorous smoke or flare mix in makes them realistic military style simulators . my neighbours have become accustomed to rocket trials if a test site in leicestershire is of any assistance pm me

[digger]

Using magnesium always scares me, maybe I will try zinc Sulphur propellant to see how good it is.

Here is a test of the fuel, 40 grams pressed to 10 tonnes per square inch into a card tube. The tube is around 40% full, note it almost immediately burnt off the top of the tube.


Fuel test

So the next stage is to find a good flame proofing for the tubes (and cored rocket design) along with maybe reducing the oxidiser content

[Arthur Brown]

A major thing for you to remember is that the "target" is actually a high value antique so extreme care with use and handling is required.

[pyrotrev]

Magnesium is OK and useful stuff as long as you remember it's incompatibilities, coat accordingly (linseed does for most things) and keep it reasonably dry if storing for a long time. Regarding your tube problem all I can suggest is to either roll your own tubes using silicate adhesive (waterglass) or impregnate with calcium nitrate then treat with sodium silicate. Whether that will stand the serious heat from a barium nitrate/Al mix I don't know, but it's likely your best option.