8 replies to this topic

[ActionTekJackson]

Now, last time I was here, we were all still using the ukrocketry forum and there were some experienced model rocketry fellas here. I've recently been studying Hybrid rockets and am completely obsessed. However, I could obtain LOx or N2O for oxidizers if I really want, but in this book I have it states that either the oxidizer OR the fuel can be liquid. So my question is, could one use something like beutane or propane as the feul and have a pressed oxidizer grain of Ammonium Perchlorate or perhaps even Potassium Nitrate? Anyone ever thought of doing this?

[newtoolsmith]

Your questions will be answered by the book "rocket propulsion elements" wich I Use and even Richard nakka does.

I am not interested in high power rocket motors very much, so I didnt think of those techniques. I only use BP or KNO3/sugar propellant.

Probably it would be the best to ask Richard Nakka. He uses KNO3/suchrose and similar fuels but he has a unbelieveable knowledge...


One word from a mechanical engineer (me):

Do you really know how difficult the needed equipment is? Its really not easy to inject liquid oxygen into a chamber in a good regulated way.

I think I am a good engineer but I would not know how to manage the many problems you will have.

MfG
newtoolsmith

[ActionTekJackson]

Your questions will be answered by the book "rocket propulsion elements" wich I Use and even Richard nakka does.

I am not interested in high power rocket motors very much, so I didnt think of those techniques. I only use BP or KNO3/sugar propellant.

Probably it would be the best to ask Richard Nakka. He uses KNO3/suchrose and similar fuels but he has a unbelieveable knowledge...
One word from a mechanical engineer (me):

Do you really know how difficult the needed equipment is? Its really not easy to inject liquid oxygen into a chamber in a good regulated way.

I think I am a good engineer but I would not know how to manage the many problems you will have.

MfG
newtoolsmith

Actually, Liquid Oxygen is Cryogenic so yes, that would be a bit more difficult to construct, however, N2O, Beutane, and Propane are simply compressed. For this all you need is an adjustible regulator between the injector and the fuel/oxidizer tank. Which can be found fairly easily at a hardware store. I'll look into that book though, and I'm going to be e-mailing Richard Nakka and John Wickman. The book will most likely help alot, thanks man.

Edited by ActionTekJackson, 02 January 2007 - 09:46 PM.

[newtoolsmith]

By the way, how many tons of payload do you want to lift?

Just kidding.

Im really looking forward to your results. The named book will help, its the rocketeers bible (for men who play with bigger rockets...).

MfG
newtoolsmith

[Ritual33]

By the way, how many tons of payload do you want to lift?

That made me chuckle.

[ActionTekJackson]

That made me chuckle.

Maybe he's right.... lol

[Ritual33]

Hmmm, I dunno; I think it's probably easier to hunt down a weapons trader and buy a small missle than to make one himself.

[Andrew]

In my experience, bi-propellant thrusters, even hybrid ones are very complicated. Just knocking one up in the shed is next to impossible. It takes years of work. The propellant storage and delivery system is the most complicated part. Chambers, throats and nozzles can be constructed from empirical data, providing you are not trying to make a micro-thruster because all the rules change.

The most pressing part is the valves, you may laugh but valves are about as non-trivial as designing a microprocessor from scratch using grains of sand. I quote from paper by Hitt el al 2001 'MEMS-based satellite micropropulsion via catalyzed hydrogen peroxide decomposition', “Valving is a nontrivial problem”, and they should know as two members of a NASA propulsion team co-authored the paper. Even at a larger scale valves are a real pain. They have to meet a vast number of design constraints.

could one use something like beutane or propane as the feul and have a pressed oxidizer grain of Ammonium Perchlorate or perhaps even Potassium Nitrate? Anyone ever thought of doing this?

Yes people have though of it before. It would overcome a lot of vastly annoying problems. BUT, using a liquid fuel and a solid oxidizer grain in the chamber is a pretty novel idea because no-one has even bothered entertaining the idea, reason being it would not work. All solid oxidizers have very low melting points, as soon as the reaction gets going you would have melted all the oxidizer grain and turned you rocket into a liquid jet (not very powerful or efficient).

Liquefied Oxygen is a miss unless you have tens or hundreds of thousands of pounds to buy and engineer the unnecessary equipment. Nitrous Oxide is a better bet, it's vapour pressure is around 56 bar at standard temperature. For non-space applications you can have a gravity fed self-pressurising propellant tank, the holy grail of propellant storage. Then as a hybrid rocket you can have a solid fuel grain, like rubber for example, and you have yourself a mini space ship one. One a down note, N2O required extensive heating and them decomposing in a catalytic bed prior to being injected into the combustion chamber. Yet another order of magnitude to add to the complexity. Then there are problems with the propellant purity, a satellite firm I know of for example, pay thousands of pounds per liter of HTP, because it needs to be MIL spec to appease launch authorities and to be any good. Poisoning of catalytic beds can occur within seconds if the propellant is crap. Rendering the whole system useless.

this book I have it states that either the oxidizer OR the fuel can be liquid.

It's more likely that you can use a solid oxidizer if you melt it and feed it in a liquid phase into the chamber. But again this is getting even more complicated. My advice is to stick to SBMs, solid composition grain rockets for now and progress to a monopropellant thruster later. Only once you have a detailed knowledge of monopropellant systems would it make sense to dive in at the deep end, the very deep end.

Liquid fueled thrusters or rockets if you like calling them that, are a minefield of bad luck and complicated engineering. I'm researching/building a micro-monopropellant thruster at the moment, you would not believe the number of design problems there are, and to top it off, launch authorities probably will not even let it fly in space, nice bit of theoretical work I've wasted my time on!!!!. If you do go ahead with it I'd love to see your work.

[ActionTekJackson]

For the most part, I'd say you're right. After reading more on the subject there are a lot of design problems, lucky for me I live in America currently, and valves and injectors are easily obtained. After some questioning I have found that solid Oxidizer hybrid motors have been tested in laboratory environments and did work, however only through the use of exotic Oxidizers, Hexanitroethane/tetranitromethane/Trinitromethane, for example. I will soon be working on a GOX hybrid motor soon, unfortunately I don't have the money to start this yet, Fiance takes priority... go figure Thanks for the input. I'd really be interested in hearing more about your mono propellant motor Andrew, shoot me a PM if ya wouldn't mind.