66% or better

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.

Comments

  1. ClutchDude says:

    A good book that discussed this was “The Art of Living Dangerously”. I think he used Dextrose instead of sugar though.

    Good book though. Walks you through the basics and gives references for you to read further.
    (http://www.amazon.com/Absinthe-Flamethrowers-Projects-Ruminations-Dangerously/dp/1556528221)

  2. Bill says:

    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!

  3. Matt says:

    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.

  4. ejonesss says:

    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.

  5. Richard says:

    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?

  6. Tom says:

    Reminds me of when I first heard of this stuff (rocket candy).

    These guys are the main men to be looking at:

    http://www.jamesyawn.com/rcandy/index.htm

    http://www.nakka-rocketry.net/

    I’ve spent many an hour admiring their work…

    Quck side note for any UK readers; Don’t.

    This (the mixutre of a solid fuel and oxidizer) would put you terribly afoul of quite a few of our laws (think Guy Fawkes…)

    Still, wicked cool stuff.

    • HomelyPoet says:

      “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.”

      • Greenaum says:

        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.

  7. Chuckt says:

    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.”

  8. Volfram says:

    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.

  9. avrpunk says:

    @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.

  10. danman says:

    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.

  11. mccoywm says:

    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.

  12. Germanguy says:

    This so reminds me of “Rocket Boys” by Homer H. Hickam.

    If you haven’t read it, do it now.

  13. bob says:

    @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.

  14. projectbluebook says:

    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.

  15. mjrippe says:

    I love the CATO reel on their site where they are doing static tests in dry grass! I’m sure they had an extinguisher handy…

  16. cknopp says:

    Good writeup… Why was I expecting thermite?

  17. MikeS says:

    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!

  18. smaddox says:

    @MikeS
    If static electricity is an issue, wouldn’t it be better to use a metal spoon, with a ground wire attached to it?

    Just a thought.

  19. rasz says:

    All you need is a pipe from a road sign.. and a hand grenade.

  20. Personally, if i was to ever do this (which i am, eventually) when mixing, igniting, etc, I’d be standing behind a brick or concrete wall. Sure, i’d have cameras on it, but screw mixing it when i’m in reach of somewhere i can get hurt.

  21. macona says:

    Here is a great book on design and testing of small liquid fuel engines:

    http://gramlich.net/projects/rocket/

  22. octel says:

    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

  23. octel says:

    For those of you interested in DIY rocketry but living in a country affected by paranoia, please check out hybrid rockets. They use nitrous oxide and a solid fuel, which can be anything from paraffin to rubber to acrylic.
    This is the same design as used on SpaceShipOne.

    http://www.aeroconsystems.com/motors/Screamer_folder/screamer.htm

  24. Tom says:

    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.

  25. Leithoa says:

    @ 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.

  26. Rachel says:

    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.

  27. i remember making these candy rockets when i was younger, they worked pretty well! i still have some KNO3 left in the house so i might make some smoke b-0-m-b-s because these things produce more smoke than thrust :)

  28. Scott says:

    The test videos rock – obviously done under cover of night. The soundtracks verge on the pornographic.

  29. Navic says:

    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.

  30. 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!

  31. macw says:

    @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.

  32. Hacksaw says:

    a couple of my friends did this 25 years ago…one of them got to pay for anew kitchen in his parents house!

  33. Scruter says:

    combining the mixture is an art. my father is still mad at me about that Hacksaw. After trying to combine the mixture in a coffee can before transfer.

  34. LARRY says:

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

    TITLE: THE ROCKET MANUAL FOR AMATEURS
    BY: CAPT. BERTRAND R. BRINLEY
    PUB: BALLANTINE BOOKS
    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.

    FUN HOBBY THAT CAN BE SAFE TOO

    LARRY

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