model rocket

Model Rockets are essentially cardboard tubes stylized after the larger, space-faring rockets. You can either build your own or purchase fairly inexpensive model building kits, such as the ALPHA III.

The model has several basic parts: the body is a cylinder usually made of cardboard or plastic. At the base it has fins (usually three, pointing out at even intervals from the body), and it has a nosecone (usually styrofoam or plastic) at the other (top) end. There is also a device to attach it to the launch rod, like a piece of drinking straw or some fancy plastic loops, on the outside.

Inside the body is a parachute, a space for the rocket engine, and some kind of buffer between them.

To launch the rocket, you take the launch pad (basicaly a stand of some kind with a metal blast plate at the base and a guidance rod sticking upward), and insert a rocket engine into the tail of your model rocket. You insert an ignition wire into the rocket engine, and slide the rocket down the guidance rod. Then you stand back, and press a button that completes a circuit with the ignition wire. It rapidly heats up and ignites the solid fuel in your rocket, hurling it skyward.

Once the fuel is expended, a small blast in the top of the engine explodes, forcing the nosecone off and the parachute out. The parachute then expands and brings your rocket slowly back to earth.

In theory, this all works very well. However, a lot of things can go wrong. Ignition wires frequently don't work properly, but this is a fairly minor concern. More often you have problems like the parachute ripping off, your rocket being carried thousands of feet away by high altitude winds, slight imperfections in the tail fins causing it to take a sharply curving trajectory and smash into the ground, the parachute not deploying, the whole rocket blowing up because the parachute deployment blast went wrong somehow, etc., etc.

That's the whole fun of them, though.

Nodeshell Rescue

Model rocket engines are usually labeled with something like this: “B5-6.”

• The letter is an indication of average impulse, measured in Newton-seconds. If the engine were expended in an instant, this would be the force it delivers.
• The number following the letter is the average thrust of the engine. This is measured in Newtons. At any given time, the force from the engine is equal to this.
• The number after the dash is how many seconds after launch until the ejection charge fires. The ejection charge fires a clay plug into the parachute, deploying it. Engines with a 0 after the dash are booster engines used in multistage rockets, and have no ejection charge.

Engines are also color coded. A single stage engine would have green lettering, while an upper stage engine would be in purple. Booster engines are in red, and plugged engines are in black. Plugged engines are for R/C gliders, and don’t use an ejection charge.

The following is a table of engine classes and fuel. Engines that supply more than 160 Newton-seconds, or engines that contain more than 62.5 grams of propellant are considered high powered engines, and require a special permit.

Class--Ave Force--Propellant

A –- 2.0 –- 1.3

B –- 3.8 –- 2.5

C –- 7.5 –- 5.0

D –- 15 –- 10

E –- 30 –- 20

F –- 60 –- 41

G –- 120 –- 82

H –- 240 –- 163

I –- 480 –- 326

J –- 960 –- 652

K –- 1920 -- 1305

L –- 3840 –- 2609

M –- 7680 –- 5219

N –- 15360 –- 10438

O –- 30720 –- 20875

P –- 61440 –- 41751

You don't need kits or parts or fins or engines to make model rockets, if all you want is a tube full of explosives that flies into the air on command.

For the tube: wrap aluminium foil around a pencil several times. Wrap a bit of tape around that (sellotape, parcel tape, whatever). Remove pencil. You now have a tube. Crimp the top of the tube and tape it shut. You now have a rocket. It's not a masterpiece of craft, but it'll hold together long enough to survive the sudden rapid forward motion.

For the fuel: zinc dust and sulphur are both cheap and readily obtainable (sulphur from a chemist, zinc dust from a chemical supplier or stolen after hours from the school chemistry laboratory, not that anyone would do that). They're safe(ish) and inert unless you set fire to them, and when you mix them together they're still safe and inert, unless you set fire to the mixture. Then it explodes. Out in the open it's not a huge explosion, just a big green flash, a "whoomp", a terrible stench, nasty smoke, and greyish-white stinky remains on anything in its path, including your fingers and face if you're stupid or clumsy. For the purposes of this writeup we'll assume you're not a certified lunatic, and know that you're playing with explosives, and need to stay away, not point into eyes, don't breathe it, don't drop them, etc. etc.

You fill the rocket with zinc dust and sulphur mixture. You crimp the tail end enough to stop it all falling out, but not enough to block it completely. The little bit that spills out the end when you stand it upright is how the fire gets from your hand to the fuel inside. Stand it up by any practical means: lean it on an upright twig, put it in a hole, whatever.

The final step is a fuse. You do not want to light the rocket fuel directly. As I suggested above, one pencilful is more messy than deadly, but you still don't want an explosion near your hand. For the fuse, you need a third chemical, potassium permanganate. This is also cheap and safe. A mixture of sulphur and potassium permanganate can be lit safely. It burns and crackles and stinks, and the fire moves slowly along it. So lay a trail of this stuff from the spilt zinc dust and sulphur at the base of the rocket, to a safe distance (20 cm away is ample).

Both mixtures can be 50/50; the exact proportion doesn't matter. Practise with the potassium permanganate and sulphur fuse first. Then practise with leading that up to small amounts of zinc dust and sulphur.

If you like a bit more fizz, you can add aluminium dust to the rocket fuel. This makes it burn brighter and faster and is, as far as I know, roughly as safe as the original. (Dusts explode.) (I forget whether just aluminium and sulphur work, or whether you need the zinc too.) You've seen magnesium burn? You can also add a touch of magnesium dust to the rocket fuel for a lovely bright effect. Or you could study pyrotechnics properly: probably better than just copying what other schoolkids did.

The fuel can be further enhanced with ammonium nitrate granules. This stuff, however, really is dangerous. It's pretty stable by itself, but it is a kind of explosive as such. There might be restrictions on its sale in these troubled times. I only ever had a 500 g jar of it; that's not quite the same as backing a pick-up truck to the factory door and saying "Fill 'er up", but the constables are paid to be suspicious. So I don't know if you could get ammonium nitrate these days without a good reason. (A reason where the words "up" and "blow" don't get mentioned in any permutation is the sort of thing I'm thinking of. I believe it's used in farming.)

You can experiment with all the details.

Back in my day we did this on school property, in school time, sometimes with teachers looking. It's probably all highly antisocial and carcinogenic these days, and they'd demand you wear full-body anti-fallout suits and sign waivers and do all the sensible things in pyrotechnics safety tips; but I'm just saying it works.

You can carry around zinc, sulphur, and aluminium mixture in a glass jar safely, but common sense suggests that, just in case, you don't do any mixing until you need to. If there's ammonium nitrate in it, don't put the jar in the back pocket of your trousers where it can slowly warm up. Trust me on this one. It warms up.