I Love the Smell of Rocket Candy in the Morning

[Grant Thompson aka “The King of Random”] has created a great tutorial on making sugar rocket motors. [Grant] is using a fuel based on potassium nitrate and sugar. Known as Rocket Candy or R-Candy in the amateur rocket community, various forms of this mixture have been used for decades. In fact, this is similar to one of the mixtures [Homer Hickam] and friends used to build rockets in his novel Rocket Boys.

[Grant] bought a cheap blender from the thrift store, which he used to grind his ingredients. You probably won’t want to use this blender for food after it’s been full of KNO3-based stump remover. The blender made quick work of grinding down the KNO3 to a fine powder. [Grant] then added in powdered sugar and carefully mixed the two by shaking, not by running the blender.

A 5″ length of schedule 40 PVC pipe made the rocket motor casing. The rocket motor’s end caps are made from ground clay cat litter. [Grant] rams the layers with a wooden dowel and hammer. First a top cap of clay, then the rocket fuel, then a bottom cap also of clay. With all the layers in place, he hand drilled a hole through the bottom cap and the entire fuel layer. Drilling all the way through turns the motor into a core burning rocket. The entire fuel cylinder burns away from the inside out, with more surface area than burning the end alone.

[Grant] tested his rocket motor at a remote location. We probably would have gone with an electric igniter rather than a fireworks style fuse, but the end result is the same. The rocket motor performed admirably, blasting up to over 2000 feet in altitude.

It goes without saying that working with solid rocket fuel isn’t something to be taken lightly. Something as simple as an air gap in the fuel could lead to a CATO, turning this rocket motor into a pipe bomb. We echo [Grant’s] suggestion to search for local amateur rocket clubs before trying this one at home.

32 thoughts on “I Love the Smell of Rocket Candy in the Morning

    1. Completely ignorant here, and not planning on building anything. Out of curiosity, would an aluminum pipe be safe? If so, how does aluminum compare to rolled paper? (You choose the pipe thickness.)

      1. Al pipe is one of the worst ideas you can have – worse even than PVC. Al is brittle and upon CATO (explosion of the engine) will create lots of high energy shrapnel. Rolled paper tube, while much thicker than metal pipe for the same strength, will produce much lighter and less energetic fragments, unlikely to cause injury over way shorter distance than metal pieces.
        I would imagine that in most rocket designs engine that transmits heat from the combustion chamber to it’s body might also be a problem.

    2. I’m willing to bet the ground clay cat litter plugs blow out before the PVC explodes.

      That being said…I wouldn’t want to be standing next to it while testing my theory.

  1. Sugar rockets are traditionally made by melting the sugar and oxidizer VERY CAREFULLY and then casting the resulting mix.

    What’s being built here is a bit different it’s a solid powder rocket – it essentially has an fractal surface area they burn REALLY fast and can go BOOM really easily. (ZnS rockets are similar, they typically use a burst diaphragm rathe than a nozzle) They also tend to be static sensitive so be careful.

    Please static test any rockets you build, from a bunker, and use an electric ignition system (donlt light the fuse and run there might be a trickle of powder down the middle when you stuff the fuse it, don’t drop them, build them at the site (don’t drive over any bumps).

    Remember a working rocket is a carefully chosen (usually by lots of test firings) midpoint between a damp squib that makes little thrust and something that overpressures the casing and goes ‘bang’

  2. Only slightly related, but reminds me of a batch of failure testing I had to do on some tubing one time. Now, this was the kind of tubing you find in power plant heat exchangers (Nuke and Coal mainly) We basically took a bunch of tubes, of various lengths, and tested them in 3 different ways. Both ends open. One end sealed, and then both ends *almost* sealed. Basically a crimp. I was impressed with exactly how much explosive material you can actually shove into a proper tube before it goes boom. We had this one tube that never even bulged with both ends crimped. After testing, we *VERY CAREFULLY* crimped the ends the rest of the way shut after absolutely filling it with powdered charge. We finally got it to fail in spectacular fashion. Or so we thought. It was found about 3/4 away from the bunker, with one crimp slighty opened.

    Ah…. I miss that job.

    *note* Yes, usually we just pressure tested by heating them to operating temperature and pressurizing, but this one company wanted actual explosive testing. I still don’t know why.

    1. Oh my god that’s an amazing job.

      I mean, I’m sure that like every job it has its boring days, but even my *best* days in this cube farm don’t involve any explosions not related to the company cafeteria.

  3. I use lead fishing sinkers in a plastic peanut butter jar to mill the saltpeter and sugar to a fine powder and then slowly melt it in a small crock pot. I roll kraft paper tubes sealed with wheatpaste and make nosecones from Durham’s Water Putty. I pack the hot fuel into the tubes, add a water putty end cap and let them cool. When they’re solid I drill the fuse hole and they’re done. I had a blast making and launching these with my nephews. It’s amazing how high these simple rockets will go.

  4. “You probably won’t want to use this blender for food after it’s been full of KNO3-based stump remover.”

    KNO3 is just saltpeter. Once thought to be an anti-aphrodisiac, and supposedly added to sailors’ food for that purpose. Still used for curing meat (aka “nitrates”), and is responsible for the pink color of corned beef, hot dogs, etc. (Although commercially, sodium nitrate is more commonly used because it’s cheaper.) I don’t make rocket motors, but I have made corned beef from scratch, using KNO3. The “smoke ring” of smoked meat is also formed through related chemistry.

    Put a little on your tongue if you like, and let it dissolve there. It tastes somewhat like salt substitute, but with a surprise – It’s endothermic (turns cold) upon absorbing water. It’s an interesting sensation.

    So *if* you’re using KNO3 (even fertilizer grade), or stump remover that you can verify is made from it alone, just wash the blender and don’t worry. If you’re using stump remover that may have other or unknown ingredients… maybe worry. Fert grade KNO3 is cheap and easy to obtain through Ebay or any number of horticultural sources, if you’re lucky enough to be in the US.

  5. Be *very* carefull trying this : potassium nitrate (chlorate works too, with the same danger) is unstable. When I was jung, one of my high school mate exploded his hand trying to make such a rocket… And remember also the explosion of the AZF plant in Toulouse !

    1. Potassium nitrate is one of the most stable oxidizers I know of. Potassium chlorate is more unstable and don’t even get me started on perchlorate.

      In AZF plant in Touluse exploded a warehouse full of Ammonium Nitrate and while it is less stable than KNO3, it still took throwing in half a ton of Sodium Dichloroisocyanurate by mistake to cause the explosion.

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