Solid Fuel Model Rocket Engines – Part 2

Good points, frankd20. Many months were invested in determining the proper geometrical shape of solid propellant "grains" (actually rods) used in military rockets such that the rate of burn would be constant throughout the burn, as the surface area of different shapes changes drastically in burning from the outside inward. If the rate of burn increases too rapidly, one is almost guaranteed to get an explosion. My MOS was propellants and explosives in the service, and we fired many different missiles at White Sands. In many cases, we also ignited the solid fuel rods by igniting a black powder initiator which shot a column of flame thru the entire length of the motor and the propellant rods. Read some technical data re the German A-4 (V-2), liquid fueled rocket, to read a really nice engineering treatment of designing a "new" concept, keeping the weight low, controlling the burn and guidance during flight, preventing the guidsance find from burning away in the rocket exhaust during flight, the pressurization of the fuel and oxidizer, etc.

The shuttles solid boosters are ignited from the top so that the flames burn down through hollow motors. They use a mixture of aluminium powder in a artificial polymer rubber binder and sodium perchlorate for the oxidiser. Whoosh it's gone.

I saw on a program on rockets in America that a propelent that used sulpher powder and iron oxide was quite common.

Ive never heard of a sulphur/iron oxide rocket fuel mix. Sulphur/zinc is quite common as a fuel, although ive never used it.

No body awake out there? You did not spot the error it should have read Ammonium perchlorate. I correct my self.

I was actually wondering about that when I read it, sodium perchlorate would work as an oxidizer, but it absorbs moisture much more readily.

Just a couple of suggestions:

A split-spool mold form for your nozzle with a dowel for centering would
give you better control for both sides of the curving shape.

You might try EMT (Electrical Metalic Tubing), of the same diameter as your
PVC pipe. (Higher temp resistance, & probably not much, if at all heavier).

For either material, a wide spiral wrapping of fiberglass reinforced packing tape
offers some control of fragmentation in the event of a burst without adding a
lot of weight.

I will offer no advice on fuel materials but strongly suggest static testing
of any formulation, as you intend to fly it, in a deep hole, before you try
to fly it. A low altitude airburst could ruin your whole day.

A simple rig with a a string pulling a spring scale located outside the
hole can safely give you thrust data for fuel/nozzle systems without
building the whole rocket.

I did things like this as a kid. I was very lucky. Be VERY careful.

Thanks for the suggestions, they are good ones. Using metal for the casing and or nozzle, as well as the tape to contain a catastrophic event are all great ideas, as well as static testing. The only benefit of PVC and a cement nozzle is its cheap and easy. This project and video was made almost 10 years ago, and I haven't done much with it since other than write this blog about it. I don't know if I will ever make more rocket engines, but if I do I would utilize some of the above mentioned ideas.

There's a fellow named Richard Nakka in Canada who's dome some nice work with PVC rocket engines, and used a mix of KNO3/Fe2O3/West Systems epoxy to make solid fuel grains for loading into PVC as well!

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

Get the website on a CD--it's well worth the money!

Allen

You claim that you were very lucky in your experiments. One could also say that you were inherently intelligent enough to know the risks and to avoid doing anything that could have had serious consequences. When I was 7 or 8, my mother bought me my first real chemistry set. I had my apparatus set out on the dresser in my bedroom, with an alcohol lamp burning. Our cat jumped up onto the dresser, knocking over the alcohol lamp and spreading flames. I had sense enough to grab a bottle of CCl4 and sprinkly it liberally onto the fire, dousing the flames (even tho to this day I don't know where I heard about carbon tet as a flame extinguisher). That was when my mother knew I was going to be a chemist. I ended up at Redstone Arsenal and White Sands Proving Grounds.

It is true that having the right knowledge and intelligence can definitely save your life and limbs. There are many things I did as a kid and that I do now that are dangerous. One thing I have always done both then and now is to research as much as possible what I am about to do. Anything I find online I confirm from other sources, and then read about other possible dangers. I don't do much with chemistry, but I have always felt it is an area that you have to be particularly careful.

You're lucky you didn't die from phosgene poisoning (carbonyl chloride) COCl₂. It has an odour of freshly cut hay it was used as a war gas WW1. They at one time made extinguishers with carbon tetrachloride until it was recognised that it could kill. Also it has been found to be a very powerful cancer causing agent. It is now banned.

None of the oxidizers or fuels I used had any variant of Cl in them, so the production of this gas would of been difficult with my formulation, but thanks for the safety tip.

Much like asbestos, carbon tet was used in horrendous quantities as a solvent cleaner until fairly recently. Think of all the shipyard workers during WW II, almost all cigarette smokers, who were daily covered in asbestos from coating steam pipes, boilers, etc with asbestos. If I remember correctly, the large caliber naval rifles were swabbed out with carbon tet to remove carbon deposits, powder residues, etc, with men in closed gun turrets. Then think of VCM, vinyl chloride monomer. It was used as a propellant in hair spray can, shaving cremes, under arm deoderants, etc, where it was most frequently used in small, closed bathrooms. We have been telling people how carcinogenic saccharin is for years, but people have used saccharin for over 80 years as a sweetener in coffee, tea and especially in soda. Food for thought.

I agree about saccharin it should be avoided.

Carbon Tet in a chemistry set. - Those were the days!

Have you seen the emasculated junk that masquerades as a chemistry set nowadays?

I couldn't agree more! Re a reply above yours, re using KNO3 etc to make solid rocket propellants, I was using KClO4, powdered Mg and powdered Al, etc back years ago, nitrating cotton, etc. Bigger bang for the buck! If you have the opportunity, go thru some of the school and college chem labs, and see the glass bottles with metal covers, and metal cans storing chemicals that love to form peroxides! Scary!