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Solid oxidiser, liquid fuel hybrid rocket.

Frozen_Heart

By Frozen_Heart
in Science & Spaceflight

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Frozen_Heart

Frozen_Heart

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I'm thinking of making a hybrid rocket in my workshop and I'm wondering what the easiest combinations of fuel and oxidiser are?

I've also noticed that every option has the fuel as the solid part. Is there a reason that the oxidiser can't be the solid part of the rocket?

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Tommygun

Tommygun

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I'm thinking of making a hybrid rocket in my workshop and I'm wondering what the easiest combinations of fuel and oxidiser are?

I've also noticed that every option has the fuel as the solid part. Is there a reason that the oxidiser can't be the solid part of the rocket?

Well strong oxidizers do have a tendency to react to things they touch, so it may be a safety issue.

You may want to look into paraffin wax hybrids.

Edited by Tommygun
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Frozen_Heart

Frozen_Heart

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Well strong oxidizers do have a tendency to react to things they touch, so it may be a safety issue.

You may want to look into paraffin wax hybrids.

KNO3 works as a good oxidiser which can be turned into a solid easily. Its also easy to work with.

Finding a liquid fuel that would work with that seems difficult though. Most seem way too reactive.

The reason I don't just make solids is that they're illegal in the UK :( Hybrids are fine though. Also more of an engineering challenge which is half the fun.

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sgt_flyer

sgt_flyer

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Well, some questions, is what you want to accomplish with it (launch an actual hybrid rocket, or only use a ground testbed to further refine your knowledge on how this kind of engine works)

Then, you asked about using a solid oxidizer and a liquid fuel - are there some technical reasons for that ? Or would you also be ready to use solid fuel and liquid oxidizer ?

In this case, this guy here

http://makezine.com/2012/10/11/homemade-hybrid-rocket-engine/

built an homemade hybrid rocket engine using plexiglas as a solid fuel and oxigen as oxydizer.

- of course, in this ground test, he uses external means to feed oxydizer to the engine - and the engine was not meant for running more than a few seconds.

In any case, any kind of pyrotechnics can be dangerous - (i know one guy who lost his hand with fireworks) so always assume the worse can happen and prepare for it :) (and then add another safety margin on your precautions for good measures)

Edited by sgt_flyer
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Kryten

Kryten

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Some kind of rubber like substance for fuel, and laughing gas for oxidizer. Shouldn't be too hard to get too. Look around the internet for a good propellant mixture.

Not terribly safe-NOX can be very unstable at the kind of temperatures and/or pressures used in rocketry, and rubber fuel can break off in chunks. If a chunk blocks your nozzle, you're not going to be having a good day.

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Frozen_Heart

Frozen_Heart

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Then, you asked about using a solid oxidizer and a liquid fuel - are there some technical reasons for that ? Or would you also be ready to use solid fuel and liquid oxidizer ?

I'm looking at solid oxidiser as oxygen gas is very expensive to get hold of where I live. Its all marketed towards commercial companies and so is very expensive. NOX is unstable so I'd rather not touch that. Liquid oxygen is a no go for obvious reasons.

This is also just very small scale and ground tests only. Saftey wise I like the idea of hybrids as the fuel isn't mixed already.

Liquid alcohol might work...

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kerbiloid

kerbiloid

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Sugar, yeast, oxidizer. Solar heater, serpentine cooler.

And you flyyyy...

Btw. What's the purpose of aluminium hybrid rocket if to melt Al out from alumina you need so much energy, that you need a compact mighty reactor. And a compact mighty reactor means you already have a a compact mighty new-clear engine.

Edited by kerbiloid
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sgt_flyer

sgt_flyer

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I'm looking at solid oxidiser as oxygen gas is very expensive to get hold of where I live. Its all marketed towards commercial companies and so is very expensive. NOX is unstable so I'd rather not touch that. Liquid oxygen is a no go for obvious reasons.

This is also just very small scale and ground tests only. Saftey wise I like the idea of hybrids as the fuel isn't mixed already.

Liquid alcohol might work...

Ok, for sure, it'll depend to how much you can invest in amateur rocketry - regarding oxygen, maybe look with diving gear stores - the initial tank buying can be expensive for sure, but the refills will not be that much. (That, or oxy-fuel welding equipments (not acetylene ones, those are expensive)

Of course, if you want to do that on long term, once you have a bottle, you'll need an industrial oxygen concentrator to do your refills yourself.

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shynung

shynung

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I'm looking at solid oxidiser as oxygen gas is very expensive to get hold of where I live. Its all marketed towards commercial companies and so is very expensive. NOX is unstable so I'd rather not touch that. Liquid oxygen is a no go for obvious reasons.

This is also just very small scale and ground tests only. Saftey wise I like the idea of hybrids as the fuel isn't mixed already.

Liquid alcohol might work...

Amateur solid rockets use potassium nitrate (KNO3) as the oxidizer in their rocket candy mix, but the specific impulse is poor. Going up, there are ammonium nitrate and ammonium perchlorate used in larger solid rockets. Should you decide to use ammonium nitrate, take great care; it is a component in an ANFO explosive.

For fuel, I recommend to use gaseous propane (or other light hydrocarbons) for its ubiquity and specific impulse. If a liquid fuel is required, in theory, flipping the propane tank upside down should yield liquid propane; the gaseous propane would float to the bottom (top?) part of the tank and pressurize it. I'd be really careful with that setup, though.

Edited by shynung
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K^2

K^2

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Yeah, if you buy any significant quantity of ammonium nitrate, expect a visit from well dressed men with no sense of humor.

There isn't really a specific reason why you can't make solid oxidizer hybrid, but there are additional challenges. Just like with solid motors, you usually want some sort of a matrix to bind your oxidizer into. Otherwise, you might end up with cracks, and the only way that can go is boom. With conventional hybrid, matrix is part of your fuel. Problem solved. With solid ox, if it starts reacting with matrix, you won't be having a good day. Unless you plan for it. But then you aren't even running a liquid-solid hybrid. You are running a liquid-solid-solid hybrid hybrid. I have no idea what British Law would say on the topic, but the judge is liable to fine you for a headache he's going to get, at least.

I'd stick with conventional hybrid and explore liquid ox options you have. There is way more out there than just NOX, LOX, and peroxide.

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Frozen_Heart

Frozen_Heart

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Yeah, if you buy any significant quantity of ammonium nitrate, expect a visit from well dressed men with no sense of humor.

There isn't really a specific reason why you can't make solid oxidizer hybrid, but there are additional challenges. Just like with solid motors, you usually want some sort of a matrix to bind your oxidizer into. Otherwise, you might end up with cracks, and the only way that can go is boom. With conventional hybrid, matrix is part of your fuel. Problem solved. With solid ox, if it starts reacting with matrix, you won't be having a good day. Unless you plan for it. But then you aren't even running a liquid-solid hybrid. You are running a liquid-solid-solid hybrid hybrid. I have no idea what British Law would say on the topic, but the judge is liable to fine you for a headache he's going to get, at least.

I'd stick with conventional hybrid and explore liquid ox options you have. There is way more out there than just NOX, LOX, and peroxide.

Any type of solid motor is completely illegal to make here so I'm pretty sure that counts as one.

Also how come the oxidiser needs to be bound into a solid? Also what unreactive substance would work for that? (And cheap substance that's easy to work with)

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Tommygun

Tommygun

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Well I guess, if you make a small motor, say 75mm long, you might get by and not use a binding material.

They don't use any on those small "candy rockets".

With a big motor you have issues with vibrations shaking the solid fuel and making it break apart.

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shynung

shynung

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Actually the sugar acts to glue the KNO3 together. I can't use sugar for obvious reasons. :/

I don't know if there's any solid-fuel binders that is stable when mixed with KNO3, yet can safely disintegrate under combustion without the substance being fuel itself. So in the end, if you make a solid oxidizer, whatever binder you'd use to bind it would be part of the fuel.

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lajoswinkler

lajoswinkler

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Stay away from ammonium nitrate. Not because of "men without sense of humor" (fu*k them), but because that's a poor rocket oxidizer. It is too reactive when the fuel sits in storage, it is highly hygroscopic and its "oomph" is pathetic when applied in rocket engines (unlike when applied in bombs, when, acting as a tertiary explosive, can do massive damage).

Go for rocket candy or, if you have the money, zinc and sulfur with binder.

I'd stay away from perchlorates if you have no theoretical/practical knowledge in chemistry. Also, never use metal for solid fuel engine casings.

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K^2

K^2

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Also how come the oxidiser needs to be bound into a solid? Also what unreactive substance would work for that? (And cheap substance that's easy to work with)

Anything that's solid needs to be bound into a soft matrix/binder. It's how you avoid cracks. Take a look at composition of shuttle boosters. From Wikipedia: "a polymer (such as PBAN or HTPB, serving as a binder that holds the mixture together and acting as secondary fuel, 12.04%)."

It's the "secondary fuel" that you'll have a problem with when building a solid fuel hybrid. But not every possible binder is reactive. I think I'd start by researching silicone options. It has some organics, so it does have some reactivity, but that's basically just going to allow it to disintegrate as oxidizer is consumed. It shouldn't be capable of self reacting under any conditions, I don't think. At least, with "reasonable" oxidizers, like KNO.

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K^2

K^2

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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.

Edited by K^2
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