Homemade Model Rocket Engines

Don'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: 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. The materials required to make the engines are very dangerous, and should only be handled by adults. Please wear a face covering helmet.

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.

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.

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.

>> Part 2