Malleable Solid Rocket Propellant

[Bacon46]

I recently had a D.I.Y. “I” series PVC rocket motor CATO (explode) approximately 30’ above the launch pad. I had static tested the motor twice with the same amount of propellant from the same batch, under very similar atmospheric conditions, without any problems. There where no visible signs of structural fatigue in the motor casing prior to launch. The only reason for this failure that I could come up with is that one of the three propellant grains had cracked due to rough handling in the loading process. The propellant grains I use are made with KN03, Sucrose and Corn Syrup and are very brittle.

Shortly after this I was at a Chinese market and found something called “Grape Sugar”. Very little of the label is in English but it appears to be 100% refined sugar derived from grapes.

For comparison, I have included nutritional information based on what it is written on the packages of both Cane Sugar and the Grape Sugar. I have calculated the Cane Sugar information to equal a 10g serving. This was the serving size used on the Grape Sugar label. The Grape Sugar figures are copied verbatim.

The “Nutritional Facts” Grape Sugar compared to Cane Sugar: (Quantity =10g)


Cane Sugar
Amount Per Serving
Calories – 37.5 Calories from Fat – 0
% Daily Value
Total Fat – 0g 0%
Saturated Fat – 0g 0%
Total Carbs – 10g 2.5%
Protein – 0g 0%

Grape Sugar
Amount Per Serving
Calories – 120 Calories from Fat – 60
% Daily Value
Total Fat – 2g 6%
Saturated Fat – 1g 2%
Total Carbs – 78g 45%
Protein – 3g

Apparently the FDA does not keep a very close eye on the nutritional information labels of imported foods. I don’t know how they arrive at these figures but something’s not right!

It doesn’t matter, it appeared to be different from Cane Sugar and I wasn’t planning on eating it anyway.:D

I purchased a 400g package of the stuff for $1.50 and a bottle of Fructose that happened to be on the shelf right above it. 8floz was $4.15

I prepared a batch of Grape Sugar and Fructose propellant using Jimmy Yawn’s Skillet Method of re-crystallization. The Grape Sugar and Fructose replaces the Sucrose and Corn Syrup in Jimmy's formula.

• 400g KNO3

• 200g Grape Sugar

• 80g Fructose

• 400mg H20.

More information on Jimmy Yawn’s Skillet Method of re-crystallization can be found at http://www.jamesyawn.com.

The end result, after allowing the propellant to cool to room temperature, was a soft malleable mass with a consistency similar to a fresh Tootsie Roll. A 1” long x .25” diameter piece burned in 7 seconds and ignited easily.

I am not sure if the softer consistency is due to the Fructose, the Grape Sugar, or the combination of the two. I will have to prepare a batch using Grape Sugar and Corn Syrup and a batch using Cane Sugar and Fructose and compare the results.

The Grape Sugar/Fructose propellant does have a lower melting point than the Sucrose/Corn Syrup propellant. I don’t have an accurate thermometer, but I had to lower the temperature in the final kneading phase. At the temperature setting used for kneading Sucrose/Corn Syrup propellant (approximately 250f), the Grape Sugar/Fructose propellant wanted to melt to a liquid with the consistency of heavy syrup.

Reproducing this softer propellant does not seem to be a problem. It could eliminate the problem of propellant grains cracking and causing excessive pressures and catastrophic motor failure for those of use who use “Candy Propellant”.

[Bert]

If the sugar is indeed derived from grapes, it should be fructose.

Some high power rocketry fuel mixes that had performed well in smaller motor designs began to produce CATO's when used in really large grains such as for experimental M size motors as I recall. The problem was traced to the fuel grains being too elastic- They actually sagged and/or tore due to the high acceleration and wider fuel grain than these composite fuels had been originaly developed with. So be aware, elasticity can be taken too far!

[Bacon46]

Good point Bert

Unfortunately a static test won’t reveal a problem like sagging or tearing grains. I wll just have to launch and see what happens.

[nbk2000]

If I remember correctly, grain sag can be prevented by having small baffles or ridges on the inner surface of the motor tube, which acts as supports for the grain against acceleration forces.

[TreverSlyFox]

Bacon46,

In your post you stated you had to lower the temp from the normal 250f for the Sucrose/Corn Syrup propellant. What temp did you finally use for the Grape Sugar one?

[Bacon46]

Bacon46,

In your post you stated you had to lower the temp from the normal 250f for the Sucrose/Corn Syrup propellant. What temp did you finally use for the Grape Sugar one?

I don’t have a thermometer that can accurately measure the temperature of the fuel in the later more viscous stages.

I would estimate the temperature at between 200 and 225 degrees Fahrenheit.

[ApJunkie]

If the viscosity of the fuel is increasing as you cook it, it's most likely from evaporation of water (your corn syrup is 30% H2O after all). You should consider using a dessicant with that propellant however, as the hygroscopic properties of the sugars can lower performance.

[Cobalt.45]

Have you done any experimenting with casting the grain while the fuel is pourable?

KNSU is a pain to cast- it doesn't so much "pour" as it does "sag" when filling rocket motor cases- especially smaller ID cases.

Your fuel sounds much more user friendly in this regard.

Much would depend on grain shrinkage. Have you noted whether this fuel shrinks much on cooling?

[Bacon46]

Have you done any experimenting with casting the grain while the fuel is pour able?

Using the skillet re-crystallization method I have always cooked the fuel until it was the consistency of very soft modeling clay at 120C.
It is too thick to pour but this fuel gives you a much longer working time than the KNO3/Sucrose/Corn Syrup formula. You don’t have to rush to get the fuel packed into grain mold. It is much more user friendly.

Have you noted whether this fuel shrinks much on cooling?

I have launched a couple of “F” series, single grain, case bonded motors with no problems. If shrinkage was going to be an issue it probably would have shown up in those motors by the grain pulling away from the case walls. Had that occurred the launch would have definitely ended in KATO.

A couple of things I have learned since I first posted this formula:

 It is the Asian Fructose Syrup that makes the fuel malleable. It can be used with sucrose, rather than “Grape Sugar”. The resulting grain is less malleable but you still get the benefit of the increased working time.

 The fuel is very hydroscopic. If left unprotected in humid conditions for any more than an hour or so you will find the fuel dripping out of the nozzle.:(

 Some of the rockets using this fuel have been slow off of the launch pad. Spitting and sputtering prior to lift off. Probably a humidity issue.

As far as the fuel being pour able; after the fuel has reached the “Soft Clay” consistency one could try gradually turning the temperature back up to 140C and continuing to knead and/or stir it. This may decrease the viscosity enough to make it pour able. You would probably end up with a harder grain in the end. I will try doing that to a batch this afternoon if I have time.

I need to get a book on candy making. There would probaly be some very usefull information on making "Candy Fuel" in a candy cook book.:D

[Cobalt.45]

The Grape Sugar/Fructose propellant does have a lower melting point than the Sucrose/Corn Syrup propellant. I don’t have an accurate thermometer, but I had to lower the temperature in the final kneading phase. At the temperature setting used for kneading Sucrose/Corn Syrup propellant (approximately 250f), the Grape Sugar/Fructose propellant wanted to melt to a liquid with the consistency of heavy syrup.
It was at this phase that I had thought the fuel might be "pourable".

If you are getting a sluggish launch, why not try a short core? This assumes you are now making case-bonded end-burners.

In any event, it's good to see something a little different being investigated in this regard. While much has been tried for making 'rocket candy', there are surely things yet to be known and tried.

I've gone as far as to making KNSU (melting it together), then powdering it to mix with black powder in various ratios.

While this works fine and rams great, it answers a question that nobody asked! I did it originally to get around the hygroscopic nature of KNSU (which it does, but it still needs to be stored air tight), and just to see what would result.

This fuel does allow me to easily add tail effects, as well as tailor it to different size/weight rockets. And I can make a large batch and store it until needed. This way I can make a rocket in just minutes.

Anyway, post any new results that you may get. Good luck.

[Bacon46]

It was at this phase that I had thought the fuel might be "pourable".

Unfortunately in that “syrupy” state the liquid sucrose wanted to separate from the KNO3.

If you are getting a sluggish launch, why not try a short core? This assumes you are now making case-bonded end-burners.

Actually I am making case bonded motors with full length cores. I only use these case bonded motors for bottle rockets. I use Bates grains for my model rockets.

The cause of the sputtering was almost certainly the affect of humidity. When inserting the fuse I noticed a small amount of fuel had run out of the nozzle at some point. The entire length of the core may have had a layer of goo that had to burn, or be ejected before the dry fuel ignited. Once it got through that stage it flew fine.

I am continuing to work on a malleable KNO3/Sucrose based rocket fuel and smoke composition, preferably one that is less labor intensive than the “Skillet Method”. I would really like to have a fuel that I could store indefinitely in an airtight container and when needed I could take it out and form it into the desired shape without having to heat it.

In my last effort I attempted to modify a Caramel recipe since this candy has the properties I desire in a fuel. (Soft and chewy). The recipe included butter but what could it hurt? It was a complete failure.:( It makes a nice smoke composition as long as you hold a propane torch to it.

It was worth a try!:o

[AWG]

Grape sugar is galactose. It is less sweet than glucose and is not very water soluble

[cpropellant]

I have found that by using d-glucose with your kno3-sucrose propellant also gives a nice malleable propellant at lower working temperatures.Using approximately 30% by weight of your sucrose works nice.Also by increasing that amount gave me a flexible propellant grain at room temperature when I applied adequate bending pressure,but after leaving the same grain to lie on its side for a few weeks,some sagging was observed.your burnrate might be altered a bit,but try using 70%kno3:30%sucrose or a burnrate catalyst.