Rocket Engines | Make Your Own Homemade Rocket Engines

Model RocketDon’t you hate paying so much for model rocket engines? The Estes engines at my town’s Wal-Mart are $1-$2 each, depending on the size. You can go through a lot of money buying those rocket engines. That’s why I decided to make my own. I found a website that told how to make some smaller engines, so I did some things a little differently so the engines would fit in my model rockets. If you make these engines correctly, they should give you about as much power as a size B engine. They should end up costing less than 25 cents each.

WARNING: Not to be rude, but if you decide to follow this tutorial and make your own engines, I will not be held responsible for your actions. If you get injured or injure someone else, it is not my fault. Please, be careful. The materials required to make the engines are very dangerous, and should only be handled by adults. Please wear a face covering helmet.
Be careful, be careful!! This can be dangerous!!!!

Rocket Engines – Making the Propellant

Ok we’ll start with the hardest part first – Finding the supplies to make the propellant. You will need potassium nitrate (also known as saltpeter), sulfur, and powdered sugar (also called confectioner’s sugar). You might be able to find the sulfur and potassium nitrate in your drugstore, otherwise you can order them online. The sugar is used as the fuel, the potassium nitrate is the oxidizer, and the sulfur releases gas to make thrust. If you can’t find the sulfur or potassium nitrate, you will have to order them online. If you buy them from a pyrotechnics store, you will have to pay a hazardous material shipping fee. So when I buy mine, I buy from an online pharmacy. 4 ounces sulfur or 12 ounces sulfur, and 6 ounces potassium nitrate or 16 ounces potassium nitrate.
You will need to mix these powders by weight, so make sure you have an accurate scale.

Powder Percent of total mixture
Potassium nitrate 63%
Sugar 27%
Sulfur 10%

So if you are going to make 10 ounces of propellant, you will need to mix together 6.3 ounces of potassium nitrate, 2.7 ounces of sugar, and 1 ounce of sulfur. This mixture allows the propellant to burn slowly, so the rocket engine won’t explode. If you just used gunpowder instead of this propellant, the gunpowder would burn very quickly and there would be too much pressure on the engine casing, so it would blow up. With this propellant, it burns slowly and releases a lot of gas, so there is high pressure pushing the gas out the nozzle, but it is not enough pressure to blow the engine up.
To mix the powders together, put them all in a clean plastic container (such as a Cool-Whip container), put the lid on, and shake it for a couple minutes. Don’t skimp out on the shaking. If the powders aren’t mixed well enough, the propellant will burn unevenly, resulting in poor performance. WARNING: Never mix these powders in a blender or anything except a plastic container. The friction created could cause your mixture to burst into flames. Even stirring it with a metal spoon could cause a spark from static electricity, which could ignite your mixture. The mixture will be a light yellow color. If you leave it in an open container, it will absorb the moisture in the air and will not burn very easily, which can cause problems when you are trying to ignite the engines. Make sure you keep the propellant in a sealed container, in a cool place, and it should last a good while.
This is a picture of some old propellant. As you can see, it absorbed some moisture and got quite clumpy.

Rocket Engines – Making the Casings

You will need to make your own casings. Do not re-use the casings from your store-bought engines, because they will not be as strong after being fired once already. To make the casings, you will need thick brown paper. Some places you might be able to find Kraft paper, but I couldn’t so I just used brown paper bags (Later I found some sheets of thick brown paper so I used that too, but I’m not sure if it was Kraft paper). To make the casings, you need to cut strips of paper and roll them into tubes. The Estes rocket engines are about 2.75 inches long, so I like to make my engines somewhere around 2.75 to 3 inches.
Because it’s tough to cut the strips perfectly straight, I like to cut them about 4 inches wide, and then I trim the excess after I have rolled them.
Lay your paper out and mark off where 4 inches is. Then measure about 12 inches the other way, and cut it out. You will now have a 4″x12″ strip of paper.

Now get a 1/2 inch wooden dowel to wrap the paper around. Begin by wrapping the paper around the dowel, until the paper meets itself. This is where you start gluing. If you don’t glue the very beginning of the wrap, you might run into trouble when you are loading the propellant. Put Elmer’s white glue all over the paper and spread it out with your finger. If you have gummed Kraft paper then you will just need to wet the paper and start wrapping, because it has its own adhesive.
Make sure you wrap very tightly so there are no air pockets. If there are air pockets in the casing, there is a good chance that the propellant could burn through the side of the casing. When you get to the end of the paper, glue it down and rub some glue over the top of it so it stays glued. Carefully pull the casing off the dowel, and set it aside to dry. Do not squeeze it because then it will not be a nice circular tube.
Wait for the glue to completely dry, and then the casings should be pretty stiff. Since we made 4″ strips and we only need the engine to be 2.75″ – 3″, we need to cut the excess off now. Make sure you don’t only trim one end though. Trims both ends evenly.

Rocket Engines – Making the Nozzles

To make the nozzle, you will need to get Durham’s Rock Hard Water Putty. Do not use any other putty, because it won’t be as strong as Durham’s. I bought a ready-to-use wood putty and tried using that for the nozzles, but it basically melted when the rocket was ignited.
You will have to mix the powder with water, however you want to do this. I usually use a paper or styrofoam cup, but I couldn’t find any when I was writing this so I just am using a styrofoam plate.
It doesn’t take much water to turn the powder into a paste, so add water slowly. If you get too much water, either add more powder or wait a couple minutes for some of the water to evaporate. You don’t want it to be too dry though, because then it won’t stick to the casings as well. So get it pretty wet. I like to mix it with my finger, but as long as you get it mixed really well, it doesn’t matter.
Now you don’t just want to slap some putty into the casing and call it good. Get the wooden dowel that you wrapped your casings around. Slide it back into the casing until it is about 1/4″ from the top (You want your nozzle to be about 1/4″ thick).

Scoop up some putty (again, I just use my finger) and gently pack it into the end of the casing. Don’t

push too hard, but make sure that it completely fills the space.

Carefully twist and pull the dowel out of the casing. Go very slow, otherwise the suction will suck the putty through the casing. Check your dowel to see if there is any putty on the tip, and make sure to wipe it off so it doesn’t dry there. Then you can flip your casing over so the nozzle is at the bottom, and set it on a piece of paper. This is better than just laying it on its side, because the nozzle will get lopsided if you lay it on its side. When it dries, the paper might be stuck to it, but that doesn’t matter.
Wait for the putty to dry overnight. If you start drilling the nozzle hole before it has dried, you will probably break some chunks off the nozzle. Once it is completely dry, use a 3/32″ or 7/64″ drill bit to drill a hole straight through the middle of the nozzle. This is pretty tough, and if the hole is angled or off centered then your rocket’s performance will suffer.
As you can see, I drilled the hole a little off-center, but it should still be OK.

Rocket Engines – Packing the Propellant

Because this propellant is slower burning than others, we can’t just pack it into the casing and light it. There has to be a core. When the core ignites, it causes more of the propellant to burn than if we just lit
the end.
Since the whole core has to be ignited almost instantly, you need to use gunpowder. How do you get such a thin core of gunpowder in there? Well you need to pack the propellant around something so that there is a hollow core in the engine so we can pour the gunpowder in. To do this, you will need to make a coring mandrel and packing tamp.
You can make a single coring mandrel, or several of them. I made 6 of them on one board so I could pack the propellant faster. I used an old 2×4 and I drilled holes partway into the board using a 3/32″ or 5/74″ drill bit. Then I cut up pieces of metal hangers (you can use piano wire, nails, or anything that has a diameter of 3/32″) and pounded them into the holes. Then I cut the tops off at 1.5″ above the wood. Make sure you drill the holes straight and make sure the wires are straight.
Now get another 1/2″ wooden dowel (do not use the wrapping/putty one) and drill a hole into it about 3/4″ or 1″ deep with a 7/64″ drill bit. This will allow you to pack the propellant as you pour it in.

Put the engine on the coring mandrel, with the nozzle at the bottom.
Funnel the propellant into the engine, in small amounts (about a teaspoon at a time).
Put the tamp in and pound it with a hammer a couple of times. Check the propellant level. If you can still see the coring mandrel wire, add more powder. When you can no longer see the wire, you are done packing the propellant.

Rip off a small piece of kleenex or paper towel and pound that on top of the propellant.

Now you need to close off the end of the engine so the only way the gases can escape is through the nozzle. You can use epoxy for this, and put 1/8″ to 1/4″ in the end, but epoxy is pretty expensive. I just use the putty I used for the nozzle. But put at least 1/2″ of it in there and make sure it is packed down against the kleenex (don’t pound on it with the tamp though).
I usually wait for the end plug to dry before I take the engine off the coring mandrel, but you can probably take it off right away. Just remember to keep it upright so the putty or epoxy doesn’t get lopsided. Also go slowly when taking it off, because you don’t want the propellant to fill in the hollow core.

Rocket Engines – Ignition

Since we packed the propellant around the coring mandrel, there will now be a hollow core in the engine. This core needs to get ingited all at once, so a fast burning powder must be used. Gunpowder (or blackpowder, whatever you want to call it) works great. Go to your sporting goods store and find the finest grained powder you can find. Pour the gunpowder into the hollow core until it is full. Then make a little pile of it on the nozzle. If you want, you can add a tiny bit of water to it so it will dry in a hard cake, but I just leave it as powder because you have to put tape over it anyways.
Get a fuse that’s a few inches long (get it from a fireworks store, or wait until I write the tutorial for making fuses) and lay it on top of the little pile of gunpowder. Get some masking tape and secure the fuse. If you didn’t get your gunpowder wet, you should completely seal the nozzle with tape so the
powder won’t fall out.

That’s all there is to it! Put the engine in your rocket and see if it works! Remember that these engines don’t have anything to pop your parachute out, so you will want to use an old rocket probably. Also watch out when it comes down, because it will be falling very fast (only launch in a deserted area).
As you can see, I have used this rocket many times (no fins and electrical tape holding the launch tube on)

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