Yes, we made rockets. Solid-fuel rockets. So ridiculously easy it should be illegal. But it isn't. We made three types of rockets: black powder, KNSU powder, and KNSU solid/mush. The KNSU powder rockets worked the best, so we'll be writing about them the most. Back in March 2011, when we were doing all this, we made a guide entitled “How to Successfully Build and Test Fire a KNSU Based Rocket Motor”. Most of what is in that guide will be on this page.
Aforementioned guide can be found here: building_knsu_rockets_guide_.pdf
Note: Sometime this spring (around mid-March) we plan on re-pursuing KNSU rockets. This page will probably be updated with pictures and videos.
All the materials needed to make simple KNSU rocket motors can be purchased at lowes and walmart in the US for less than $50.
- Hot glue gun with extra glue sticks
- Staple gun
- Drill w/ an array of bit sizes
- Table saw (or some other way to cleanly cut dowels)
- Scissors/Razor blades
- coffee grinder
- Scale with 0.1g precision - 0.01g preferred
- Trays to weigh the fuel in
- Paper towels and water to wipe up spilled fuel
- Fire extinguisher
- Table vise (for static tests)
- Large/Spacious work area
- potassium nitrate - Can be found as “stump remover” from stores like Ace Hardware or Lowes. Expect to pay $7/lb. The brand “Spectracide” worked best for us.
- Sugar. If you're going to cook the fuel, use sorbitol syrup. Any kind will work. It's just an easy carbon source.
Non-Fuel Expendable Materials
- Heavy brown craft papers. Often sold in rolls 3' wide.
- Wooden dowels, 3/4“ in diameter. Oak is best.
I think that a lot of people rush to make the fuel first, before making the casing, when it comes to these types of rocket motors. KNSU fuel is incredibly hygroscopic, and all exposure to even slightly humid environments is going to want to be minimized as much as possible. The more moisture the fuel absorbs, the less powerful it becomes.
You can begin building the casing for the motors in a few different places. We tended to start with the dowel work then make the tubes, as we had to do them in completely different locations and it was much more convenient to do the dowel work first. We started with getting several of the 3/4” oak dowels and then cut them into two sizes of disks - some 1/4“ thick, the others 1/2” thick. The thinner dowels form the top of motor and the thicker dowels form the nozzles.1) Cut as many cap and nozzle pieces as you think you'll need, plus a few extra to compensate for screwups and issues.
You will need another piece of dowel about 6-7“ long to use to form the case and pack the fuel. Make sure not to cut this one up.
Now, get the roll of brown paper and cut a strip about 4” wide across the length of the entire roll. Do this for as many motors as you want, plus extra. It's incredibly easy to mess this part up, and will take a lot of practice to get good at. In theory, it's incredibly simple: roll the paper around the piece of dowel you set aside. It has to be rolled as tightly as possible, and in a perfect cylinder. When it's finished, tape the edge and remove the dowel with a slight twisting motion. If you do it right you'll have a perfectly made cylinder of brown paper with a fairly thick wall. These rarely failed - most failures were regarding the nozzle.
Make a bunch of these cylinders and set them aside.
With the hot glue gun, run a bead around one of the 1/4“ thick pieces of cut dowel. Push this piece into one of the openings of the cylinder. Re-insert the dowel you used to shape the case (or you could have left it in, whatever) and staple the dowel piece into place. Pay attention to the orientation of the grain of the wood - if you staple it along the grain you may very well split the piece, making it entirely useless. Prep all the other casings this way.
Making powder based KNSU propellant is about a hundred times easier than making black powder. If you can mass and grind powders, you're set. I can't remember exactly how much propellant our motors could hold, I think it was between 30 and 50g. To get started, make enough for one motor and continue doing that until you get a good feel for what you're doing.
KNSU propellant is 65% potassium nitrate and 35% sucrose. We always used table sugar because it was the easiest to get our hands on. To make a batch small enough for one motor, weigh out 20g potassium nitrate and 11g sugar. Put both of these components into your coffee grinder and pulverize them until the mixture looks just like powdered sugar. This will create very sharp grains that tend to clump together in weird little clusters - this is a good thing.
Put this fuel in a tupperware container (or something else with a good seal) and load it as soon as possible.
Loading the Propellant
To start loading the propellant, make a paper funnel or something else to control the flow of the powder. As you pour it in, use the spare dowel and a hammer to compact the powder as much as possible. Hammer the dowel straight down so as not to split the paper case. That can happen more easily than you'd imagine. Once all the fuel is loaded and compacted, get one of the thicker piece of cut dowel and mount it in the bottom in the same way: with a bead of hot glue and two well placed staples.
Drilling the Core
The core size is one of the primary determining factors in how well your motor works. If the core size is too large, the rocket will flare out. If the core is too small, internal pressure will build up enormously and the motor will explode - usually within less than a second of ignition.
We used bit sizes between 1/8” and 1/4“. Larger holes tended to work better. Hold the motor steady and drill down the middle of the thicker dowel through about 70% of the motor body. If the propellant was well packed only a small amount should fall out.
Get this out of the PDF.