Homemade Solid Propellant Rocket Motors

[KoD] and [Navic] are building solid propellant motors using sugar and potassium nitrate. They cook up the two ingredients along with water and a bonding agent. They find that corn syrup is particularly good for bonding and that cooking the strange brew is more of an artform than science. Either way, the video after the break is proof of the dangers involved in this hobby. Testing the engine thrust with a bathroom scale ends badly for the scale.

There is something satisfying about the ingenuity that goes into the materials. For a casing they’re using PVC pipe, and forming a cone to focus the thrust by using a what amounts to plumber’s epoxy putty. The capping agent for the finished motor is ground up kitty litter.

This is an interesting read, but for now we’re going to stick to water rockets.


42 thoughts on “Homemade Solid Propellant Rocket Motors

  1. Just figured I’d drop a note, as this is a hobby I am in to.

    Experimental rocket motors are a lot of fun, but definitely are a time and money consuming hobby – don’t jump in if you want to fly cheaper than commercial reloads, it won’t happen.

    Also go slowly and be careful. While these processes can be safe, be prepared for the worst case scenario, work small, refine. It took me months to get to my first static test, and over 1.5 years to my first flight!

  2. There’s a whole group of hobbyist rocketeers that make their own motors (“research motors”). Typically research motors are safer than what is being built here. Instead of PVC and epoxy putty, they use machined aluminum cases with metal closures and real machined graphite nozzles. There is some initial investment, but with proper construction, research motors can be just as safe as commercially made motors.

  3. as soon as you get a new scale you could try turning the rocket upside down and have a rig to hold it in place and fire it into the scale.

    by doing it upside down the the flame shoots up and you may just dent the cone if you are lucky.

    also for safety you may want to do this outside because the smoke who knows what is in the smoke.

    also you dont want to burn down your house or breath the gases from the rocket.

  4. they probably arn’t getting enough back pressure to justify that size of expansion ratio, hay it might not even be supersonic. Some of the motors also seem to suffer combustion instabilities (popping and buzzing noises) possibly the throat is too small?

    1. “Remember, Remember, the Fifth of November, the Gunpowder Treason and plot, for I know of no reason why the Gunpowder Treason should Ever be Forgot.”

      “VoilĂ ! In view, a humble vaudevillian veteran, cast vicariously as both victim and villain by the vicissitudes of fate. This visage, no mere veneer of vanity, is a vestige of the vox populi, now vacant, vanished. However, this valorous visitation of a bygone vexation stands vivified, and has vowed to vanquish these venal and virulent vermin vanguarding vice and vouchsafing the violently vicious and voracious violation of volition! The only verdict is vengeance; a vendetta held as a votive, not in vain, for the value and veracity of such shall one day vindicate the vigilant and the virtuous. Verily, this vichyssoise of verbiage veers most verbose, so let me simply add that it’s my very good honour to meet you and you may call me V.”

      1. Oh gods, the film was *terrible*! Read the book, dude! Reduce the world’s level of sucking ass!

        Still, it can be ignored, I’ve only really seen it twice, and soon recovered from the rage-induced stroke I had after seeing how horrible, clumsy and thick-headed the whole thing was.

        Seriously, the book is so good! One of the few best books I’ve ever read! The film is a cheap insult, but then that’s Hollywood.

  5. My relatives are into model rocketry and they read about this guy who would cook his motors in the oven and hold a fire extinguisher with one hand and eat popcorn with another. He allegedly set his kitchen on fire more than once.

    A man who works in the industry said his boss had to read two stacks of books on static electricity because even the professionals have problems. Usually they are made in a building in Arizona or somewhere where there is lots of desert so they don’t harm anyone and occasionally they need a new building because the stuff destroys the building. What are you going to use to mix the stuff? Are you going to use motors? That produces static electricity.

    I was discouraged by an article I read by a twelve year old called “The Day I blew my fingers off.”

  6. Cool stuff! Rocket engines are very difficult to find these days.(I’ve heard the Estes model rocket company went out of business. Sad days.)

    ejonesss: they did. It provides very little thrust for several seconds, and then smashes the scale.

  7. @Mat “Typically research motors are safer than what is being built here.”

    No, aluminum tubing is not safer that PVC, but PVC is not very safe either.

    A safe motor will use a stiff paper tube, and bentonite (aka kitty litter clay) nozzles. If it malfunctions due to a crack in the fuel grain it will blow up without throwing metal fragments through your eyes and brain. Keep metal out of it, same with lumps of epoxy, etc.

    For bigger motors (beyond backyard rockets/fireworks), you should probably go with liquid fuel and oxygen, then you need metal, and it’s a whole different thing with different safety requirements. The reason is that it’s more difficult to make sure the fuel grain in a solid rocket of size doesn’t have cracks in it.

  8. So I have Sodium nitrate, but no potassium nitrate. I’m finding it very hard to get. Would the sodium version work? I have tried burning it before, I have observed it burns a solid orange vs the purple of the potassium.

  9. Potassium nitrate aka stump remover at Lowes, or any other home store. Also be careful there is a large whole in the kitchen table from my younger days messing with this stuff when I had a batch ignite.

  10. @danman
    Sodium Nitrate will work much like potassium nitrate but you won’t get the cool blue flame :)

    This is a lot of fun. The best one I made jumped over a wall backwards during a static test: The end cap blew off (putty) and it made enough thrust out the top to actually fly :)

    garden centre staff in the UK look at you funny when you ask for fertilizer that contains potassium nitrate :D

    I got some potassium or sodium nitrate off ebay in the UK and no swot team appeared at my door but I was never quite sure how legal buying it was. I reckon buying it is fine but mixing it with sugar makes it an explosive and making an explosive without a license gets you in a lot of trouble. I think there are amateurs with licenses in the UK but it’s a whole lot of trouble.

  11. yeah, KNO3 is not a good thing to have around unless you know exactly what you are doing and have a thorough knowledge of antistatic precautions.

    Interestingly a little while ago I read about a guy who made solid rocket motors using used motor oil, epoxy (the boat repair stuff FWIW) and bubbled oxygen through the curing mix while spinning it at just the right speed to make the bubbles distribute in the correct pattern for a smooth burn.

    needless to say unless you are experienced this is best avoided as well, considering that O2 is known to make even non explosive materials ignite violently with no warning .. !

    btw under the Stasi (cough Nu Labour /cough) laws even ordering the materials can get you in “deep doodoo” so watch out.

  12. I remember a book about this… Their recipe was melted Caramel cubes, into which the KNO3 was mixed. Caramel is (lets face it) sugar with a binder, and it should be easy to deduce the actual sugar content so you can plug it into his recipe.
    The caramel is melted in an electric temperature controlled frying pan, outside, please, and stirred with a wooden spoon. The other bonus is, it’s easy to cast in it’s melted form, and I suspect, it’s not brittle when hardened. Probably smells nice too! Please be careful!

  13. DIY rocketry results in explosions, sooner or later. it’s best to not be in the way of shrapnel, but faced with a choice between metal or plastic shrapnel I’d choose the metal any time.

    PVC won’t show up on an xray and exploratory surgery isn’t fun at all

  14. Since 9/11, doing without official permit, anything that has to do with pyrotech or explosive compounds, has been “up-rated” from being punishable as a misdemeanor to a felony in many states and countries. In some places, public opinion on doing things like this goes right with child molestation. No. I’m not making this up.

  15. @ danman, yes sodium nitrate will work, but your fuel will absorb more water from the air than it would if you had potassium nitrate.

    A lot of their engines seemed to be very poorly constructed. Rather than pour in the propellant they should tamp it in, this would reduce the sputtering and CATOs they’re experiencing.
    Ideally the entire motor assembly should be mounted on a mandrel that forms the core whilst tamping in the fuel.
    Priming the core with black powder would increase performance of their engines and ensure a more uniform burn rate. There are black powder recipes that only use charcoal and potassium nitrate so they wouldn’t have to buy anything else.

    P.S. Keep your propellant grains under ~65g to keep the BATFE happy.
    +1 for nakka rocketry.

  16. Static electricity is not an issue with this mixture. Sucrose is fairly hygroscopic, so the water tends to dissipate any charge. Nor is the mixture impact sensitive.

    In my opinion, the most dangerous part of this is melting the mixture. It’s very easy to ignite this way. I make all of my rockets by pressing the finely powdered mixture into the tube. The performance difference is negligible.

    I agree with PVC casings being a bad idea. Polyethylene or cardboard is the way to go. If an explosion occurs, PVC creates shrapnel, polyethylene splits harmlessly, and cardboard isn’t massive enough to hurt anything. I prefer used roman candle tubes.

    Bentonite nozzles work very well, and I’ve also had good luck with plaster. Never use fuses to ignite homemade pyrotechnics. Always use electrical ignition so you can stay as far away as possible. It’s very cheap and easy, so there’s no excuse not to. I have a couple guides on my website.

  17. Thanks for all the comments guys! If I knew where to get N2O I’d do up some hybrids for sure. Might have to look deeper into that stuff when I get a chance.
    @MikeS – thanks for the caramel cube tip! I’m gonna try that out for sure, mostly because casting our mixture after cooking must be done very quickly due to the hardening factor.

  18. Great video and a great project. Very dangerous though – especially reading about drilling through the fuel mixture to allow proper burning. My uncle and a friend of his made a similar mixture and encased in in metal pipes (to blow up dead tree roots). The friend hammered the pipes generating heat and probably a spark – igniting the mix. He now only has 1 hand. Please be careful!

  19. @alex — that’s because your dad’s friend made what is called a “pipe bomb”, not a rocket engine. As people have been saying, using a cardboard or polyethylene (think plastic milk jug material) tube will reduce the risk of a dangerous explosion. You might get a big fireball and burn off some hair but you’re much less likely to lose anything that won’t grow back.

  20. The best resource for this kind of thing I’ve found is:

    COPYRIGHT 1960

    I used the instructions in this book as a kid in the 60’s put Rockets up several thousand feed. Some groups broke over 100,000 feet.

    The book goes into great detail on how to do things safely. It covers sugar based propellants as well as zinc/sulfur propellants in detail.

    It is long out of print but used copies show up at bookfinders.com from time to time. I have also been told that it can be downloaded but haven’t been able to find it.



  21. Lack of uniformity in the density of the rocket engine ….or “bubbles” in the solid structure…..can lead to DDT or deflagration detonation transition. KABOOM! This DDT phenomenon is quite interesting….especially if it can be controlled. ;-)

  22. Coming into this very late because I didn’t know about the article until 15 Dec 2018:

    Some background: I’ve taught college/university chemistry for 36 years, co-authored six editions of two chemistry textbooks, given one or two small pyrotechnics shows annually for over 20 years, written articles for the late “Extreme Rocketry” magazine, and made rocket motors of various types for almost 30 years. I still have all ten fingers. :-) This is gonna be long, so you’d better go pee before you start reading…

    –I’ve always tried to avoid using the words “safe” and “propellant” in the same breath; “low hazard” is preferred. A G-motor containing just two ounces of low-hazard propellant (APCP) can lift itself and a well-designed rocket a mile into the air, nearly reaching mach 1 on the way up…..and close to that speed on the way down, if it comes in ballistic.

    –The sensitivity of a pyrotechnic mixture to spark, flame, friction, impact varies enormously depending on the mixture’s composition and preparation Examples: black powder (KNO3:charcoal:sulfur) is highly sensitive to sparks and flame but quite insensitive to pressure and impact. Armstrong’s mixture (KClO3:red phosphorus:Sb2S3) is extremely sensitive, period; it has been known to ignite simply from carelessly opening a container of the mix. OTOH ammonium perchlorate composite propellant (APCP), the sort of mixture used in space boosters, can be quite difficult to ignite deliberately, let alone accidentally. An extremely detailed list of impact sensitivities of various compositions can be found in “Fireworks from a Physical Standpoint, Part IV” by Takeo Shimizu

  23. Continuing:
    –Aluminum tubing is more hazardous than paper casings, much less hazardous than PVC. The vast majority of commercial high-power motors use aluminum casings; most of these will handle pressures well in excess of 1000 psi.

    –Nakka’s site describes “sugar” motors in tremendous detail. Sorbitol and other sugar alcohols as the fuel with KNO3 oxidizer are less hazardous and melt at much lower temperatures than table sugar mixtures. These types of propellant provide considerably higher specific impulse than blackpowder, though less than APCP.

    –Liquid and hybrid engines/motors involve a lot of plumbing and engineering and early efforts are much more likely to undergo a RUDE (Rapid Unscheduled Disassembly Event :-)) than solid motors. It’s worth noting that the Tripoli Rocketry Association ordinarily allows only APCP and “sugar” motors at its Research launches. Homemade liquid/hybrid engines require special permission from the BoD.

    (I am attempting to post additional comments but HaD isn’t letting me do so, at least so far. Says I’ve already posted them… :-/)

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