Hybrid Rocket Engine

----- Disclaimer -----

Matt from the future here:

Don't build this. It was designed by a high schooler (me, several years ago) with only a vague concept of how rocket engines actually produce thrust.

I do not reccomend building a fully functional thrust-producing hybrid rocket engine at home using parts from the hardware store. While this project worked mostly as intended and did not cause safety issues, that was more out of sheer luck than proper planning. The design and operation of this "engine" is not safe and should not be replicated. You have been warned.

That being said, there is some relevant information related to engines and the science behind them in this Instructable, as well as some practical considerations. For those reasons (as well as limitations on the delete-ability of published Instructables) I have chosen to keep this instructable online.

----- End Disclaimer -----

Rockets are awesome. This is an undeniable truth.

Many years ago, when I first discovered model rockets, they captivated me. Those little gunpowder engines had just enough thrust to make a painted cardboard tube soar hundreds of feet in the air.

In this instructable, we will build a slightly more complicated hybrid rocket engine, and re-ignite my fascination with machines that spit fire. Also, we will find a more creative way to destroy that pile of old math homework in the corner of my desk.

Before we get started, a note on safety:

This project uses oxidizer (in this case, just oxygen) to make a cylindrical section of solid fuel burn very very quickly. This can be seriously dangerous and problematic if not handled correctly. It never hurts to do a little extra research before you start a project like this, and you can never have too many fire extinguishers nearby.

Proceed with extreme caution. If you have absolutely no idea what you're doing, then it's probably best not to try this at home.

And with that out of the way, let's get started!

Step 1: Materials and Tools

Again, DON'T BUILD THIS

Materials:

• I have chosen to remove the list of materials so that this project cannot be easily replicated, see my previous disclaimer for a more complete reasoning

Tools:

• various pliers and wrenches
• metal clamps (for the test stand)
• thread tape
• safety goggles
• fire extinguisher (though I hope you won't need it)
• a healthy fear of fire
• a small amount of patience
• and a camera

Step 2: Science!

Before we build our model engine, let's review the science behind rocket engines.

If you're just here to see this thing spit fire, feel free to skip this step. If you want to learn about rockets, stay a while and watch the video.

Pretty much every rocket ever (with the exception of toys that use air or baking soda or whatever) use some sort of combustion reaction to produce hot gas, make it move really quickly, and create thrust. If you're familiar with the fire triangle, then you already know that combustion requires three things:

1. heat
2. fuel
3. oxygen

Usually, fire takes advantage of oxygen in the air and heat from an ignition source. In this case however, we are gonna give it a little boost. With an extra source of oxygen, the fuel will burn much faster. At a certain point, the fuel will burn fast enough to produce thrust and behave like a rocket.

For our design, I will start by using paper (old math homework) as fuel and a 1.4 oz oxygen bottle as the source of oxidizer. Held in a steel pipe with a modified end cap to act as a nozzle, this should safely produce a small amount of thrust.

Step 3: Assembly

The whole thing is assembled pretty easily from plumbing parts. It is important to keep some thread tape between each set of threads to help keep an airtight seal. This will prevent oxygen or hot exhaust from leaking out the sides.

To make the nozzle, I flattened out a spot on the top of the steel end cap and drilled a small hole. I should have just used a stepped drill bit, but instead I started small and just worked up to about a quarter-inch hole. Using a much larger drill bit (about 1/2 in.), I then tapered the sides of the hole to better resemble the shape of a rocket nozzle.

The nozzle will screw on to one end of the steel pipe, while adapters for the oxygen will attach to the other. You'll need to put fuel in the rocket before everything is sealed up, so I recommend waiting to attach the nozzle until after the fuel is inserted.

Matt from the future here: Note that none of this is good practice when assembling a real rocket engine. Add that to the list of reasons not to replicate this project.

Step 4: Fuel

So you've probably figured out by now that a hybrid rocket engine requires two completely different kinds of propellant. The first kind will be the fuel itself, which can be literally anything that burns (wood, sawdust, wax, plastic, even meat). For this project, we'll start by using paper and work up to more exotic fuels. The second thing we need is oxidizer. In this case, we're going to be using pure oxygen gas. Nitrous oxide works just as well, but I don't have any laughing gas on hand, so we'll stick with the oxygen bottles you can buy in the hardware store.

Let's start by making a fuel grain out of paper. You'll need lots of scrap paper (I used a pile of old math homework), some tape or glue, and patience. (This could get a little tedious) I started by tightly wrapping a piece of paper around a metal rod about the width of a pencil. Tape that piece of paper in place so it doesn't unwind, then repeat. Keep adding paper until the diameter of the paper tube is an inch. The paper fuel tube should fit snugly into the steel combustion chamber. Make sure a small hole at least 1/4 in. wide runs through the middle of the paper tube. This hole will be critical in getting the engine started.

After you've done that, set up the oxygen tank.

Matt from the future here: I've removed the rest of the instructions on this page because they are a massive safety hazard. Don't work with pure oxygen unless you know what you're doing.

Step 5: FIRE!

But before we fire this thing up, it's important to review some basic safety precautions:

• make sure the area is cleared of flammable material. Keep the rocket at least 10 feet away from anything that could catch on fire
• make sure the engine is securely mounted to something that won't move. I clamped mine to a heavy-duty saw horse.
• keep a fire extinguisher at the ready
• I sprayed the whole area with a garden hose before starting the engine. This prevented any possible debris from starting fires in the grass
• wear eye protection
• do not ever put any part of your body in the path of the engine flare. Use metal pliers to ignite the engine, not your fingers.

Disclaimer: Rockets are really dangerous, so use extreme caution. I am not responsible for your actions, you are.

Alright, now we can get ready to light it.

Here's the initial procedure I followed, thought I do not recommend repeating this:

1. make sure all hoses are connected and the oxygen valve is completely shut off
2. grip a match at a 90 degree angle with a pair of pliers so that your hands are not in the path of the engine flare
3. light the match and begin adding a small amount of oxygen (matches were a bad idea)
4. insert the match into the nozzle and increase the flow of oxygen. the fuel should begin to catch fire
5. increase the flow of oxygen and take a step back
6. to stop the burn, shut off the oxygen completely and allow a few minutes for the engine to cool. submerse any unspent fuel in water to ensure no risk of fire.

Here's how it probably should be done:

1. make sure all hoses are properly connected and the oxygen valve is completely shut off
2. insert a model rocket engine igniter into the engine nozzle. Ensure that the igniter is wired to a proper launch controller
3. begin to add a small amount of oxygen into the combustion chamber
4. ignite the engine by pressing down on the launch button and the launch key on the controller
5. increase the flow of oxygen until a consistent burn is reached
6. immediately shut off the flow of oxygen if the engine begins to behave unexpectedly.
7. after shutting off the engine's oxygen supply, give it a few minutes to cool completely. Submerse any remaining fuel in a bucket of water to prevent unexpected fires.

Matt from the future here: this is how you should do it:

1. don't. If you need to actually light a rocket engine, you should consult the engine's manufacturer and not read about it from an Instructable that some kid (me) wrote a few years ago.

Step 6: Going Further

Just about anything can be used as the solid fuel for a hybrid rocket. Paraffin wax, PVC, and plastics are common and effective, but nearly anything that burns can be used as fuel.

Matt from the future here: this is only sort of true. I am aware of at least one hybrid rocket that burns cheeto dust. In practice, thrust-producing engines use only a select few possible fuels and most of those are far too energetic to be used in a project like this.

If you enjoyed this project, please consider subscribing to me on YouTube. I don't post projects often, but I try to make them interesting and fun to watch.

If you'd like to learn more about hybrid rocket engines:

• https://web.stanford.edu/~cantwell/AA283_Course_Ma...
• http://www.spacesafetymagazine.com/aerospace-engin...
• https://copenhagensuborbitals.com/history/technolo...

Comments

[elliott.kim]

If I may ask, how long does this burn for when using the whole oxygen tank?

[pat_pending]

Nice Instructable mate. Agree with the comments about thrust but you mentioned this was a model of a hybrid engine and not something 'flight ready'. If you do want to make a flying rocket, the R-Candy solid fuel that Grant Thompson (A.K.A the king of random) makes works well and is pretty safe using the safety precautions you are taking already. Regarding the 'danger' of what you're doing: at school the teacher would use liquid oxygen and dip a biscuit in it then touch it with a long match/splint. This thing would explode with a wild bang! Guess things weren't dangerous in the 80s. It's a small wonder the human race survived at all :-) . Keep making. Stay safe

[LabRatMatt]

I've flown solid fuel rockets many times before, and I've seen Grant's video on the topic, but I find other forms of propulsion fascinating. Yes, oxygen is dangerous. I cannot legally obtain liquid oxygen though, so I won't be doing anything crazy like that.

"Guess things weren't dangerous in the 80s" is probably the best single sentence I've read in this entire comments section.

[Tecwyn Twmffat]

Obviously safety is an issue here, but what happened with your math grades? Could I use my annual tax return as rocket fuel as an effective tax avoidance scheme?

[LabRatMatt]

Hahaha, the math homework had already been graded, and my grades in math were rather high. My math teacher however, had a tendency to assign a series of long and redundant math problems for homework, giving me a special hatred for the long and redundant problems. I had long joked about hosting a burn party with classmates who shared my views on the assignments, but I decided to destroy the papers with a little more flare instead. 0

I do not endorse any tax avoidance schemes, but that would certainly work as fuel.

[bpark1000]

You need to ignite the engine at the end where you inject the oxygen (could be done with electric igniter inserted all the way in). The "rocket's" success isn't verified unless you measure its thrust-time product.

Be careful, the pipe could explode! You should have secondary containment.

Be careful

[LabRatMatt]

Thanks for the information. It's highly unlikely that it will explode as it cannot build enough pressure to damage the steel, but thanks for the concern. I will re-evaluate that before testing any other types of fuels.

[jdbwizzard]

For a further safety concern you could use a remote rocket launch system to ignite an ematch. I build solid rocket engines and this is how a test fire them so I can be in a safe place while I light them. Good information though.

[LabRatMatt]

I'm thinking of building a much safer ignition system in the future. Using a match wasn't the best idea.

[Tesla_Shock]

Watch Grant Thompson's video on how to make liquid Oxygen and Nitrogen. Combine the two as Oxidant and Combustible, and you get the most efficient rocket that has been (publicly) created to date! If you're feeling a little dumped with liquid Nitrogen, try Alcohol ( 90% or higher is preferable) or Kerosene, like the Germans and Werner Van Braun in WW2. Just be prepared for your contraption to belch black smoke. If you have no idea who Van Braun is, go check him out! You'll be surprised. I'd leave liquid oxygen in the mix, unless you're in the states, because Oxidizers are hare to find. The most popular oxidizer variants to Liquid Oxygen are Hydrogen Peroxide, but for that you need 80% or more and is virtually impossible to find without having a lot of contacts in the chemical industry, or making it yourself, or Potassium Permanganate, which isn't really sold outside of the states (I lived in the states for a looooong time and did this stuff a lot but then I moved to the EU where EVERYTHING IS GOD DAMNED CONTROLLED FOR THE SLIGHTEST POSSIBILITY OF EXPLOSION! AAAARGH!) Anyway, good luck and hit me up if you have any other questions!

[thormj]

Just be really careful with Tesla_Shock's answer... if you mix LOX with some things, it burns really well. If you mix LOX with other things (eg but not limited to, Alchohols), you have an pipe bomb instead of a rocket motor because the flame front is too fast to get out of the nozzle... and it can be unsafe/unstable for -hours-.

Find a Tripoli / NAR club, look up and understand flame fronts and grain designs, and start understanding how a rocket nozzle works and why it is important. Unintended consequences can go from pipe-bombs (why you should use a remote igniter and have a safety shied around the test stand) to 300 feet horizontal launch, lighting a huge fire, and even to more oh-crap-moments.

But a great launch is beautiful to behold. Best of luck and *be safe*!

[LabRatMatt]

I wrote a school paper on Van Braun a while back! I plan on keeping this project a little more simple, as I don't have enough chemistry experience to attempt anything with fancier oxidizers, but I know someone who does. I also live near the east coast of the US, so liquid oxygen is hard to come by. I might eventually get around to some more complex experiments but not until much later. Thanks for the info!

[MichaelAtOz]

I'd suggest a blowback preventer/flashback arrester/whatEvaYaCallIt

https://en.wikipedia.org/w/index.php?title=Flashba...

Particularly if you go to more potent fuels.

[LabRatMatt]

thanks for the link! I will look into that for future tests

[Michal Choma]

nice,

[BudD3]

Experiment.

This is not a "rocket" engine. This is nothing more than a dangerous experiment.

GWR1 said it all. He told it like it is.

[PaulA23]

Research. This is nothing more than someone researching the physics of what makes a rocket work, and is no more dangerous than a "real" model rocket. There isn't any "telling it like it is" because the OP has already REPEATEDLY noted the dangerous nature of the project, as well as the valuable lessons learned. Whatever happened to experimentation and (God forbid) helping, thereby increasing knowledge for all who stumble across the information?

[LabRatMatt]

Yes, this project is dangerous. Fire always is. But this is still a fully functional model of a hybrid rocket engine not unlike those used on suborbital spacecraft (though suborbital spacecraft engines are not usually made from hardware store materials). There appears to be an argument brewing over the safety of this particular project and the nature of dangerous projects on Instructables. I took lots of off-camera precautions and did much research before I even started this project. I knew the risks and how to mitigate them, and I just hoped to share the project and my experiences with this community.

[AlphaOmega1]

Nobody has to make your prototype hybrid rocket engine (which it clearly is). We live in an age (as mentioned above) where nobody wants to take responsibility for their own actions, yet happy to stand around waving their 'holier than thou' flags with no personal cost; yet it gives them (they assume) the moral high-ground. They are usually the ones that never achieve anything. Anyone can point after the event.

I say top marks for your design and planning. You could easily have spent twice as long writing a RA, and yet nobody was hurt despite that! Joining a rocketry club is probably a good idea (although I could just as easily give many reasons for that not being a good idea - you'll be near other people with rockets for one!)

I'm keen on extreme sports, and as a kid blew stuff up with my own explosives (chemistry is fun!), even made my own bullets using casings from a fun fair. Launched Greek fire balls from a home-made Roman catapult, blasted around on motorbikes (of course), taught myself to repel off of railway bridges, on and on! Why am I here in one piece all this time later? I think about and understand the dangers, and don't trust my life to other people.

I have to post a letter in a moment, I don't have a RA, but either way, I could die getting to the post box - such is life.

Live life, be safe and don't be put off.

[LabRatMatt]

Thank you! Those extreme sports sound exciting, but a they sound very dangerous (even to the kid with a can of compressed oxygen and a match). Best of luck with those extreme sports, and try not to hurt yourself on the way to the post box!