Wax motor resources?

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Well-Known Member
Nov 7, 2004
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Does anyone have any URLs/pointers to the Stanford/NASA Nitrous Oxide/wax motor project documents and related resources? At least something other than the Aviation Week articles? I've kind of hit a dead-end on finding anything more technical than what would be printed in Popular Science magazine level stuff. Wax (literally Hurricane Candle Wax in a tube) is theoretically a higher Isp/lower VOC propellant compared to HTPB, yet quite a bit cheaper.

Harm none,

I've been working on a N2O/wax hybrid. There is a group up in Oregon that has done some GOX/wax work that is very interesting. I'll try and find the link. As for wax, the only complaint I have is that it shrinks a lot unless you add some other plastics to it. I was going to fire the hybrid tomorrow, but with high temperature of 21 degrees, no gas is flowing.

Thanks. I managed to find one paper by a stanford student/prof team covering the techniques they used, but I haven't had much of chance to go over it. However, I have managed to glean a little bit of useful info from the other articles that I have found.

- The NASA/Stanford motor is a "spin cast" motor, meaning that they fill the tube to the "filled" percentage of its finish volume, and then spin it at 1500 rpm around the long axis to prevent bubbling/cracking as it hardens.

- They added carbon black powder into the wax to prevent permature melting, as well as to stabilize the material to thermal shock affects.

- Exhaust gasses are environmentally benign (Water, C02, etc).

- Isp is ridiculously high for the total cost of the motor, and approaches/surpasses some Liquids.

I'll keep digging tommorrow and see what I can find.

Harm none,

RW- the one paper I've seen on the topic was available from NASA Tech Briefs. I guess it is probably the same paper you found already.

someone pointed out that wax is not as easily machinable as harder materials such as PVC (and sausage!) so may not be appropriate for semi-production amateur hybrid motors.

the emphasis of the research was a restartable hybrid motor. they certainly acheived that. are amateurs are interested in restartable motors?
Bill Colburn runs a forum called Hybriddyne:


Here you will find good info on here that can help. I have a friend on that forum who is working on many formulas for paraffin designs.

Currently he has a Hexamine/sucrose/wax formula; a sorbitol/wax and plain wax w/ graphite powder for opacifier. He has also used printer toner for an opacifier as well.

On sunday Dec 5th I will trekk to Russ's house with a number of other guys for a day of gilling motors and burgers.

The centrifuge or "spin cast" was also used to force the paraffin shrinkage to the outside of the grain, instead of to the inside. The grain was spun until it was cool, there by forcing the the grain to shrink outward. The grains I have made so far, shrink so much that the cast tube will slip right off of the cooled grain in about 5 hours time.

Paraffin is such an awesome fuel. It melts quickly and literally burns like a liquid. One problem Russ was able to semi overcome was the problem of the grain collapsing into the flame front as it softened up. Nylon window screen. He cut off a length of it, attched it to the mandrel, and let it unwind til it stopped against the casting tube.This created a spiral web that allowed the liquid paraffin to flow thru. In a since, as the motor ran, the nylon mesh gave the grain stability inside the chamber. It also became fuel and was consumed.

Russ's motors are awesome. They light instantaneously, burn with a yellow and red flame and are chocked full of mach diamonds. As I watch some of the video of the straight paraffin grain, there is no smoke either.

Edward, I was wondering where you have been, glad to see your working with hybrids, particularly paraffin...so what plastics are you adding? So far I have trieed Vybar 103 and stearine but the end reult is the same.
I've been using an acrylic liner to cast into. I also figured if I used it and I used all the wax fuel then I would have some acrylic to burn - two birds with one stone. I have been using really low melt was - 130 F. I just heat it up until it barely melts. I have a friend that is big into candle making and she told me to heat it the minimum amount. To 2 lbs was I add 10 long HOT TEMP melt glue sticks. This gets rid of some of the fragility of the wax and helps with the shrinkage. Hot glue is ethelyne vinyl acetate - but you can't find it many places. To get them to melt you have to get the wax to about 300 degrees, melt it in, then I cool it until it hardens and then barely heat it back up. Hopefully next weekend I will fire this puppy up.

Oh, and if you want to see the mach diamonds and the mass flow better - get yourself a welders glass plate - shade 5 - and put that on the front of your video camera. It helps tone down the brightness and makes the diamonds stand out.

Use google and google scholar to obtain more info on wax hybrids. Unfortuately many of the references from google scholar are from professional technical journals that require a fee or membership for downloading.

You shouldn't be surprised that the specific impulse of wax is high. After all, the only difference between methane, propane, gasoline, kerosine (RP-1), fuel oils, wax and lubricating oils, bunker oil, and tar and polyethylene is the the number of carbons in the molecular chain.

The generic chemical formula for a saturated hydrocarbon is CnH(2n+2).

Methane is CH4. Propane is C3H8, gasoline, kerosine, fuel oils, wax and lubricating oils, bunker oil, and tar are mixtures of hydrocarbons have average molecular of C5-C10, C10-C16, C14-C20, C20-C50, C20-C70, C70 and larger respectively.


Polyethylene is a simply a polymer of ethylene with the formula CH3(CH2)nCH3 where n is a big number.

The biggest physical difference between the different classes of hydrocarbons is that some are gases, some are liquids and some are solids, and that the liquids and solids must first vaporize before they react completely.

They all react the same way in a rocket motor, and when they burn make CO, CO2, H2O and H2 in varying amounts depending on the oxidizer to fuel ratio.

The great advantage of a wax hybrid is that has the inherent simplicity of a solid and the Isp of a liquid. The primary problem with wax is that is that you have to add an Infrared opacificer (1-2% carbon black, not graphite) to it so that the thermal radiation from the flame does not melt the wax in depth. Other than that, it's a great fuel.

You can buy waxes that melt from 100 F to 600 F, and you can even buy black wax that is a high melting wax containing carbon black and used in industry for the temporary sealing of leaks in vacuum systems. Not all waxes have high shrinkage near the melting point either. It pays to shop around for the properties you want. https://www.mcmaster.com has a fairly wide variety of waxes if you want to experiment.

Some black polyethylene rods and tubes contain carbon black and are the machinable equivalents of black wax suitable fo hybrid experiments.

Bob Krech
This is great. My bookmarks file just exploded in size! Looks like I have more reading to do. I should be able to get somewhere with all this.


I like the idea of the nylon screen "loose rolled" in the core, sounds like a very simple (possibly elegant?) solution to the fuel core sloughing problem. Mixing hot glue in with the wax might be slightly more effective, if slightly fussier, solution overall. When you do get a chance to launch these motors, let me know how they went. I wish I was somewhere I could do basic testing on this. Maybe I should try applying to Scaled or SpaceDev. But then I'd have to *shudder* pay Californian taxes.

bobkrech: Thanks for the URLs.

And yes, I do have a near insatiable level of curiousity about things I'm interested in.

Harm none,

So, if I want to spin cast something...can I just put my liner tube in my drillpress...plug the bottom of my casting tube, full with the proper amount of wax and let the drill press go? It can't be that easy can it?


Ping Bob Fortune at Aerocon, he has all the particulars on Stanfords work with spinning the grain. They had it down so that with the right amount of paraffin, when the grain was cool, the core was already present from the centrafuge action. I have been looking for a high speed wood lathe on the cheap.

Hobby Lobby has 130 degree wax in 10 pound slabs for $9.99.

What brand glue stick, or does it matter?
Our Hobby Lobby had them on sale for $5.99...don't know if that is just us. I bought a pack of from Walmart, the purple high temp ones that are about a foot or so long. It really thickens up the wax mix :)

I was thinking that it would create a core when you spun it....might have to try that tonight!

I was drilling the cores into the hybrid Saturday and noticed that the wax with hot glue added felt a lot more like soap than wax. No waxy feel and felt like Dove soap chips. Just an observation.

I was talking to a friend on the phone about my hybrid motor and he suggested Jewelers Wax. What a great idea! The green kind can be machined and melts at 240 F. That is really nice and high temp and is already opaque. I'm going to get some this week for this weekend.

Originally posted by edwardw
I was talking to a friend on the phone about my hybrid motor and he suggested Jewelers Wax. What a great idea! The green kind can be machined and melts at 240 F. That is really nice and high temp and is already opaque. I'm going to get some this week for this weekend.


Jeweler's wax?

For carving lost wax molds for metalworking, or lapidary wax for holding cabs?
For lost wax casting. The green stuff with a melt temp of 240.