Best beginner rocket fuels?

[Idobox]

For hybrid rockets, the fuel of choice appears to be rubber: it's cheap, high energy, easy to find, and doesn't melt too easily. You can buy it in liquid form with a catalyst to make it into a solid.

You can produce your ow LO2 by using LN2. The boiling point of LO2 is higher than that of N2, so simply pushing air through a copper coil immersed in LN2 will produce some LO2. The process is pretty inefficient, since air is composed mostly of N2, but if you can get your hands on O2 tanks, it's not that bad.

Be aware that oxygen is dangerous in high concentrations. Don't let anything combustible anywhere close, not even brunt matches. Stuff you thought has burnt can catch fire again, stuff that burns can explode, sometimes spontaneously.

Concentrated sulfuric acid is another strong oxidizer, but it's dangerous as hell (you might know it under the name vitriol).

[lajoswinkler]

Rubber is a great fuel if it's intimately mixed with an oxidizer. I think that's actually used in spaceflight. SRBs perhaps, with perchlorate of ammonia...

Sulfuric acid as an oxidizer in rocket? That won't work. It needs to be very hot, and the reaction rates aren't high. I can't imagine it being used in engines.

About LOX - if it drips on wood or asphalt or anything combustible, and you strike it, detonation occurs. LOX is a vixen and I'd prepare it in situ. Tank of LN2, coil and tank of O2, leading to the fuel tank. The setup should be on gravel or sand.

I don't know how much experience OP has with these things... if he doesn't have any, I'd sincerely recommend solid rocket motors.

[Idobox]

Sulfuric acid will react fast, but not with everything. All in all, it's better to avoid it anyway.

Rubber, I've seen used in large amateur hybrid rockets.

Any strong oxidizer is to be treated with a lot of respect, but if you want the stuff of nightmares, check this

http://pipeline.corante.com/archives/2008/02/26/sand_wont_save_you_this_time.php

Handling large flows of strong oxidizers is not easy, and solid rockets can be very good. They even sent LADEE with one.

If you want to improve performance, you don't have to limit yourself to rocket candy.

[K^2]

Rubber is what's frequently used, but there is rubber and there is rubber. If you just buy a big chunk of rubber and cut it into an engine, odds are, you'll have problems with cracking, which can cause detonation, and who wants that?

The reason I suggested paraffin wax is that it's easy to obtain, it is cheap, and it is easy to work with. Yes, it tends to heat up and run in chunks for larger motors, as C. Suborbitals noted, but OP isn't going to build anything large enough or running hot enough for long enough for it to truly be an issue. Not on the first attempts. Temperature and ISP are going to be OX pressure limited, so it doesn't really matter.

And have any of you guys actually tried liquefying O2? It's a pain. First, you have to get all the moisture out of the air, or your condensation tube will freeze shut. Then you have to get rid of CO2. It will also cause problems, albeit, not as severe. Only then you start getting good quantities of LO2. And then you have to deal with corrosive effects, the cryogenic temperatures, etc. And all of that assumes that you already have a huge quantity of LN2 sitting ready, because you are going to be wasting that like crazy.

Edited October 7, 2013 by K^2

[DaveofDefeat]

Solid rocket fuel would be a lot easier.

[K^2]

Honestly, it depends. An efficient solid booster constantly rides on the verge of running out of control. There is a positive feedback. Higher pressure means higher reaction rate, which results in more pressure. With the hybrid, you have some negative feedback as well. Higher pressure reduces oxidizer flow.

But if you are going to play it safe on the pressure, sacrificing efficiency, yes, solid motor is about as simple as rockets get. And having some experience with custom solid motors is a good introduction to hybrids.

[dharak1]

I feel so special getting help on rockets from Copenhagen Suborbitals! I know paraffin is weak but not that weak! I guess I will use rubber. Keep in mind initial tests with stationary rockets will be done on my grandparents acreage until I can buy some super cheap land near Drumheller AB. I hear it can get as cheap as 250$ an acre. What kind of rubber were you talking about that starts liquid? Is it some supersaturated thing I can make or should I just order it?

[lajoswinkler]

Rubber is what's frequently used, but there is rubber and there is rubber. If you just buy a big chunk of rubber and cut it into an engine, odds are, you'll have problems with cracking, which can cause detonation, and who wants that?

The reason I suggested paraffin wax is that it's easy to obtain, it is cheap, and it is easy to work with. Yes, it tends to heat up and run in chunks for larger motors, as C. Suborbitals noted, but OP isn't going to build anything large enough or running hot enough for long enough for it to truly be an issue. Not on the first attempts. Temperature and ISP are going to be OX pressure limited, so it doesn't really matter.

And have any of you guys actually tried liquefying O2? It's a pain. First, you have to get all the moisture out of the air, or your condensation tube will freeze shut. Then you have to get rid of CO2. It will also cause problems, albeit, not as severe. Only then you start getting good quantities of LO2. And then you have to deal with corrosive effects, the cryogenic temperatures, etc. And all of that assumes that you already have a huge quantity of LN2 sitting ready, because you are going to be wasting that like crazy.

It can be dealt with a series of washing bottles with a rich solution of lye and one container with a bag of dry lye inside. No CO2 and water will get through that. The worst problem is the efficiency which will be paid in LN2 boiloff.

But LN2 is relatively cheap. For what it's worth, if someone is trying to build a liquid fuel rocket, copious amounts of LN2 shouldn't be a problem.

[JakeGrey]

Any strong oxidizer is to be treated with a lot of respect, but if you want the stuff of nightmares, check this

http://pipeline.corante.com/archives/2008/02/26/sand_wont_save_you_this_time.php

I was going to jokingly suggest dharak1 try that stuff as a fuel, but then it occurred to me that there's probably someone in China selling it whoilesale.

[shoveycat]

You better post a video of this....

[dharak1]

I wouldn't expect one too soon I need to do testing with this stuff.

[JakeGrey]

I think that was what shoveycat was hoping for video of. Especially the parts where things go wrong in an amusing way.

[Copenhagen_Suborbitals]

I feel so special getting help on rockets from Copenhagen Suborbitals! I know paraffin is weak but not that weak! I guess I will use rubber. Keep in mind initial tests with stationary rockets will be done on my grandparents acreage until I can buy some super cheap land near Drumheller AB. I hear it can get as cheap as 250$ an acre. What kind of rubber were you talking about that starts liquid? Is it some supersaturated thing I can make or should I just order it?

We use Polyurethane, its a 2 component that you mix then pour. You can see more about our tests here http://copenhagensuborbitals.com/testoverview.php

[dharak1]

I see. I will for sure read that when I get home from school. The people in the video used polyurethane but in the clear hoses you can buy.

EDIT: Read the page and looked at a few rockets like Baby heat and Heat 1x. I want you guys to know you are my inspiration and I doubt I will ever do anything as amazing as you. I hope this rocket works and if it does I will keep going. You will be the first people I mention if I ever get anything to space proper.

Edited October 9, 2013 by dharak1

[dharak1]

I found some urethane mixes not sure they are meant to be burned. Here they are: http://www.smooth-on.com/Urethane-Rubber-an/c6_1117/index.html Would any of these work? If they do I am one step closer to a rocket. If they don't where do you buy yours? While I wait to find urethane I need to sak the construction teacher at my school if I can use the metal lathe at school to thread some pipes and make a nozzle.

[BeefTenderloin]

As a note for people interested in the UK -- Solid fuel rockets are illegal to manufacture under the explosives law, but hybrid and liquid fuel engines can get around this! Because neither of the propellants in hybrid motors are explosive on their own, they bypass the law, and because liquid fueled engines' propellants only meet at the source of ignition/ combustion chamber, then they are also legal.

Now, I tried looking for sales of L02 and LH2 in the UK but I could only find unrelated searches. Considering some other oxidiser like nitric acid -- can someone help me with this?

[K^2]

Concentrated nitric acid is a horrible pain to work with and not easy to obtain anyhow. As it has been suggested earlier, the easiest oxidizer to obtain in most places is N2O. Sale is prohibited in some places due to its use in car modifications, but I don't think possession is prohibited anywhere in Europe. You might want to double-check on that. So you should be able to order it if not in UK than somewhere nearby in Europe.

[BeefTenderloin]

Is there a way to figure out an oxidiser:fuel ratio? I imagine certain substances will do a better job than others at oxidising the propellants, and also that some propellants will be more oxygen-hungry. If we've established that LNO2 is the best oxidiser to get hold of in the UK, what about propellant? Gasoline? Petrol? I'm looking at an LFE due to it being legal by UK laws.

[K^2]

Use the reaction formula to determine stoichiometric mixture, then go slightly fuel rich.

[BeefTenderloin]

Won't I need to figure out how many of the oxidiser/propellant molecules are in a given mass/volume?

Anyway, LH2 is probably unfeasible in the UK, and things like RP-1 are both a no-no under explosives law (probably) and require refining equipment. The only manufacturing equipment I have to hand is the school's DT department and the only access to chemicals and the equipment to refine or condense materials is the school's science department.

[K^2]

RP-1 is just kerosene. (Known as paraffin in UK.) It is definitely legal. LH2, even if legal, will be more hassle than it is worth.

And yes, stoichiometry will tell you how many molecules of each you need. You use that to get mass fractions by first considering masses of molecules involved. (For RP-1, or any other hydrocarbon, assume you are burning CH2, so molecular mass is 14.) Then you'd look up densities of the relevant materials to determine volume rations if you need these.

By the way, all of the above should be really easy for you if you are building a rocket engine. If you are having difficulties figuring out how much of what fuel/oxidizer your rocket will burn, you should not be building a rocket engine. I guarantee you that you are also missing a whole bunch of critical knowledge that is required to do this safely. Learn the theory first, then learn all of the safety stuff, and only then should you proceed to trying to build something.

There are ways to do all of this with relative safety, but there are also a lot of ways to hurt yourself and others.

[dharak1]

So would that urethane work? I would love to get a working engine by new years.

[K^2]

It will. Like I said earlier, almost anything organic will work. Some things work better than others, and there are many ways to prepare polyurethane resulting in different firmness and density. You need to find a mix that will get firm, dense, and without any foaming or bubbles in it. (Some urethane polymerization schemes are specifically designed to give you a foam. Avoid these.)

[rhoark]

I have yet to lift a finger on this plan, but I'm thinking were I to build rockets, I'd follow an incremental path:

First a compressed air rocket, not expected to go far, but a testbed to work out valve control, telemetry, fins, parachutes, etc.

Next learn about refrigeration and put together a liquid air generator.

Update the first rocket with a thrust chamber and nozzle to produce thrust from the thermal expansion of liquid air.

Finally, with most of the groundwork already done, graduate to a bipropellant rocket with kerosene and liquid air.

[dharak1]

Sounds like a good plan to me. I might steal it. I still need to order stuff like accelerometers, urethane and other things.