27 replies to this topic

[digger]

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.

These don't get fired at actual vehicles / tanks etc, but dummy bunkers etc which are rigged to blow up with either a charge with fullers earth etc or fireball produced by one or other means.

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

Yep I agree magnesium is OK if coated. I usually roll my own tubes, I will have a little bit of an experiment with sodium silicate. Calcium nitrate do you mean calcium chloride?

[pyrotrev]

I usually roll my own tubes, I will have a little bit of an experiment with sodium silicate. Calcium nitrate do you mean calcium chloride?

Calcium nitrate is more often used for this as it's available as a fertiliser and exceeding cheap. Calcium chloride, acetate or any other soluble calcium salt would sort of work
(the idea is to impregnate the paper fibres with a precipitate of calcium silicate), though when I tried the chloride the tubes never really dried due to deliquescent un-reacted CaCl2, so you'd need to make sure there was an excess of silicate.

[MDH]

You might as well use calcium sulfate. It's very cheap and is a great binder (as it is mostly used). You can quickly wet some over a tube you're rolling with a paintbrush.

Edited by MDH, 14 December 2007 - 08:44 PM.

[digger]

You might as well use calcium sulfate. It's very cheap and is a great binder (as it is mostly used). You can quickly wet some over a tube you're rolling with a paintbrush.

OK I'll give that a go (I have Calcium Carbonate, Sulphate, Nitrate and chloride).

I launched my first finished rocket tonight with the propellant. It was 21mm ID 7.5mm to 5mm core 55mm long and 12g of bentonite for nozzle (works out to be around 15mm in height leaving 40mm core in the propellant). I was hoping it would only go up 30m - 40m nice and slow. It growled (interesting sound sort of a mid pitched crackly rumble, not the whooshhhh of a bp rocket) off into the sky bloody quickly to an estimated 300ft+ before the motor stopped and it disappeared (leaving a residual blue stripe on my vision for a couple of minutes).

So it looks like a bigger nozzle will be required to slow the motor down a bit (tried one without a nozzle and it could just lift its own weight, 180g initially).

So back to the drawing board for the tooling.

[MDH]

I also discovered calcium sulfate is used as a fire retardant in vancouver buildings, interestingly enough so that's a double.

again I'm a little concerned your tube could be charred very quickly however, as calcium sulfate does react with aluminum in high heat conditions. I believe it is often used to make strobe or flash compositions that way, which is something I definitely should have mentioned in my previous post but managed to slip from my thoughts.

How has it gone so far?

Edited by MDH, 23 December 2007 - 05:46 AM.

[digger]

I also discovered calcium sulfate is used as a fire retardant in vancouver buildings, interestingly enough so that's a double.

again I'm a little concerned your tube could be charred very quickly however, as calcium sulfate does react with aluminum in high heat conditions. I believe it is often used to make strobe or flash compositions that way, which is something I definitely should have mentioned in my previous post but managed to slip from my thoughts.

How has it gone so far?

I haven't done any tests yet with an inhibited tube (will do some tests soon), however cored motors seem to fly well (too well for the original purpose of the fuel) (an end burner as you rightly point out is a non starter). I was going to fire a couple tonight, however I have been dragged round all day delivering presents to relatives. So it looks like it will be a couple of days before I can fire any. I will post a few pictures and possibly a video if my camera doesn't just white out with the brightness of the motor.

Edited by digger, 24 December 2007 - 08:32 AM.

[Arthur Brown]

Calcium sulphate is the formal name for Gypsum ie Plaster so it's used as fire retardant everywhere you have plaster/plasterboaed.

[digger]

Calcium sulphate is the formal name for Gypsum ie Plaster so it's used as fire retardant everywhere you have plaster/plasterboaed.

Doh should have noticed that one.

[Draco_Americanus]

if you want a slower rocket why not try adding more mass to it? not the most technical way to make it slower but it may work, lead bird shot would be my first choice for adding mass to the rocket

[digger]

if you want a slower rocket why not try adding more mass to it? not the most technical way to make it slower but it may work, lead bird shot would be my first choice for adding mass to the rocket

I have considered more mass, however we wish to keep the mass reasonably low (certainly at the end of the burn) for safety reasons. When testing to get the correct motor size on first motors we used some of the faster ones hit the end of the wire line so hard that they ripped off the guide tube and launched. From this we learned that it was best to get the motor as light as possible and get the right speed by dialling in the fuel and the construction tools to make sure the rockets hit the end of the line with the minimum energy possible.

[Draco_Americanus]

perhaps a felt or leather liner for the cable tubem, that may add resistance and allow for some brakeing? just a thought

[digger]

Well, I did a test tonight with the same tooling that I have used before with this formula. The only difference was that I ball milled the barium nitrate, Sulphur and the boric acid together before adding the two types of aluminium powder. It would appear that this made the fuel no easier to light, the first test rocket did not light from the fuse (silver flying fish doubled over and pressed tightly into the core). The second attempt lit, but instantly cato'ed (this is my first cato since starting to press motors).

So I now have a few options, 1. abandon this formula and maybe pursue something with a KP base oxidiser 2. try to modify it make it easier to light and to slow it down a bit.

In any case does anyone have any ideas for either of these options.

P.S. here is a quick clip of the cato (excuse naff camera)

[Draco_Americanus]

just let me make the fuel, it will eaither cato or not have enough thrust, my luck with rockets is mixed lol