Solid oxidiser, liquid fuel hybrid rocket.

[Frozen_Heart]

Using cheapest materials isn't always the greatest idea in rocketry. I do understand trying to be thrifty with the stuff, though. Just be careful. And if you do end up causing trouble and anyone asks, you got all your advice on 4chan.

P.S. And by the way, the most important advice in this thread was given on the previous page. Do not use metal parts. That stuff will explode. There will be shrapnel. In rocketry and explosives, safety rules are written in blood.

Eh? I thought that the combustion chamber and nozzle pretty much had to be metal?

Also I'm making sure any tests are done surrounded by earth banks and with no one in direct line of sight.

Edited December 7, 2014 by Frozen_Heart

[K^2]

With solid/hybrid motors, your combustion chamber is surrounded by your solid fuel (or oxidizer, as case may be). If walls of your combustion chamber got hit, that means your fuel burnt through. Avoid that by making sure liquid runs out first. All the walls have to do is hold the fuel (or oxidizer) together against the pressure in the chamber. They do not need to be very heat-resistant. Indeed, hobby rocket motors are made out of cardboard. Of course, you might have to deal with more pressure, so maybe some sort of plastic would be good. But something non-brittle, so that you don't get with sharp edges on shrapnel when it does explode.

Nozzle does have to withstand high temperatures, but here the situation is opposite. Temperatures are too high. If you build your engine right, metal nozzle will simply burn through, and you'll loose pressure causing your engine to fizzle out. Or, you know, spray liquid fuel all over the place and light up whatever's near. One or the other.

Best material for nozzle is carbon. That stuff sublimates at 3900K, which is way, way higher than any metal. And it cools itself as it does so. It's also pretty easy to work with. It's not cheap, but you shouldn't need anything bigger than a five pence in diameter, and maybe a few mm to 1cm thick.

[shynung]

I think PTFE (Teflon) can be considered as a binding agent. According to the Wiki, it's a polymer that melts at 327 degrees C, and fairly non-reactive. It has been used as an oxidizer in pyrotechnic compounds with powdered metals as fuels, producing mainly elemental carbon (soot) and metal fluoride, along with lots of heat. Often used as igniters in common solid-propellant rockets.

Watch out for those fluorines, though.

Edited December 7, 2014 by shynung

[sgt_flyer]

I thought teflon above 350° Decomposes and the byproducts were toxic ? Not the kind of stuff you'll want to work with in amateur rocketry. (Can cause the deaths of animals at least)

[Frozen_Heart]

I tested PVA wood glue and KNO3 and they didn't react together, even when heated. Would that work as a binding agent?

[shynung]

I thought teflon above 350° Decomposes and the byproducts were toxic ? Not the kind of stuff you'll want to work with in amateur rocketry. (Can cause the deaths of animals at least)

Hence the warning. Teflon starts to deteriorate at around 260° C, byproducts of which have been known to be lethal to birds.

Though, we're using it as an oxidizer mix here. Temperatures are going to be significantly higher, and there'd be fluoride compounds going out the nozzle. If the fuel is a hydrocarbon, probably most of them will be HF.

EDIT: PVA would qualify as a fuel rather than oxidizer. It'd work as a binding agent, though you're practically making a solid propellant mix rather than a solid oxidizer.

Edited December 7, 2014 by shynung

[Frozen_Heart]

PVA would qualify as a fuel rather than oxidizer. It'd work as a binding agent, though you're practically making a solid propellant mix rather than a solid oxidizer.

It didn't seem to react at all when I tested it?

[shynung]

It didn't seem to react at all when I tested it?

Maybe not by heat. PVA in wood glue has the chemical formula (C4H6O2)n. The carbons and hydrogens would be the fuel atoms.

Try testing it with an open flame; be careful when doing so. If it didn't react with KNO3, then it shouldn't burn as a fuel, and I'd be wrong.

[Frozen_Heart]

Maybe not by heat. PVA in wood glue has the chemical formula (C4H6O2)n. The carbons and hydrogens would be the fuel atoms.

Try testing it with an open flame; be careful when doing so. If it didn't react with KNO3, then it shouldn't burn as a fuel, and I'd be wrong.

This was tested with a direct blowtorch flame. Only in tiny quantities. If it does react though I'll have to find another binding agent.

I'd rather do a normal hybrid but NOX isn't available at all around here and gas oxygen bottles cost hundreds. :/

[Kryten]

In a rocket, it's going to be under high pressure as well as temperature.

[shynung]

This was tested with a direct blowtorch flame. Only in tiny quantities. If it does react though I'll have to find another binding agent.

I'd rather do a normal hybrid but NOX isn't available at all around here and gas oxygen bottles cost hundreds. :/

Make sure you're using some remotely-operated mechanisms when testing it. I've known a few persons in my lifetime who has lost fingers due to fireworks.

[K^2]

I can guarantee you that PVA + KNO3 will burn. In fact, you can make a solid fuel rocket out of just these.

[QuesoExplosivo]

Better yet, use polyvinyl nitrate (the nitrate ester of polyvinyl alcohol). That will give some interesting results!

[Frozen_Heart]

I can guarantee you that PVA + KNO3 will burn. In fact, you can make a solid fuel rocket out of just these.

Hmm. Maybe I just got a duff batch of KNO3...

I'm going to avoid Teflon if its going to have fluoride compounds coming out of it...

[Frozen_Heart]

After a bit of research it seems propane fuel and KNO3 oxidiser could work. Both are very easy to handle and use. I have the facilities to construct a nozzle and combustion chamber easily so those are sorted.

However finding a binding agent is still problematic.

[shynung]

However finding a binding agent is still problematic.

I'd recommend to avoid anything that has a hydrocarbon group. That's going to be a fuel in the resulting solid grain. What you're looking for in an oxidizer are halogen-group elements, things like oxygen, fluorine, and chlorine.

Edited December 7, 2014 by shynung

[Frozen_Heart]

I'd recommend to avoid anything that has a hydrocarbon group. That's going to be a fuel in the resulting solid grain. What you're looking for in an oxidizer are halogen-group elements, things like oxygen, fluorine, and chlorine.

What would be the cheapest and most easily available of those?

[shynung]

What would be the cheapest and most easily available of those?

I don't have anything to compare it to, but I know that Teflon is available for the general public in many forms. I'm not sure I know how to get it legally though, in your locale at least. Whether you're OK with having fluorine compounds out your nozzle, that's up to you.

[Frozen_Heart]

K^2 mentioned silicone as a binding agent. Is that likely to be reactive with the fuel?

I can't see it as even remotely flammable enough to react with oxidiser by itself.

Hmm these google searches for these various chemical reactions are likely to get a knock at the door from men in suits by themselves...

[K^2]

I still say it's better to go with something relatively inert, like silicone, than hunting for something with halogens in it.

Edit: It really shouldn't react by itself. It might add a bit to fuel as it disintegrates, but not significantly. That said, I have never tried mixing silicone with an oxidizer. And you do have to be careful with curing agents. Some of these will readily ignite with oxidizer. But there are plenty that will not.

[shynung]

I agree with K^2's suggestion. Silicone should be the way to go.

Well, technically, it'd be a fuel, but it's relatively inert compared to the actual fuel. That might be good enough for government work.

Edited December 7, 2014 by shynung

[Frozen_Heart]

Trouble is any that ignite with the oxidiser on their own are not allowed. That will also just be a solid motor...

Would simple silicone sealant work and not react. That stuff is dirt cheap and easy to use so that would be wonderful if it could be used as an inert binding agent.

[shynung]

I suppose further oxidizer tests are required. I'd try to torch the mixture, to see if they react.

[K^2]

Would simple silicone sealant work and not react. That stuff is dirt cheap and easy to use so that would be wonderful if it could be used as an inert binding agent.

It's a type of silicone rubber. So it's going to depend on curing agent and amount of carbon and hydrogen present. I think you'll have to do tests, as shynung says.

[Frozen_Heart]

Fingers crossed that it will be suitable.

What ratio of oxidiser to binding agent would work? It has to be able to stick together but there still be enough oxidiser to react with the propane.