The best kind of fuel for model rockets?

[BadRocketsCo.]

Ah, thank you very much! But if I use Aluminum as the BODY of the rocket (I could get free aluminium pipes), is that ok?

[lajoswinkler]

Ah, thank you very much! But if I use Aluminum as the BODY of the rocket (I could get free aluminium pipes), is that ok?

If the engine is in a plastic high pressure pipe (the ones used to transport water) which is inserted into the rocket, that's ok. If the engine casing itself is made out of aluminium, problems will occur, so I advise against it. Also, in case something goes horribly wrong, you don't want a pipe bomb made of metal.

You should make your rocket out of cardboard or lightweight, thin and sturdy plastic material, and your engines out of those thick plastic pipes.

It would be very bad if your rocket's parachute fails (or you don't install it, which is often illegal) and an aerodynamic metal pipe is hurling towards the ground. It's a missile, and the speeds involved are insane.

Basically, this.

https://www.youtube.com/watch?v=tCgNWiBzvYo

The sound of such thing is very creepy. It whistles, just like a real missile.

[Armchair Rocket Scientist]

If the engine is in a plastic high pressure pipe (the ones used to transport water) which is inserted into the rocket, that's ok. If the engine casing itself is made out of aluminium, problems will occur, so I advise against it. Also, in case something goes horribly wrong, you don't want a pipe bomb made of metal.

You should make your rocket out of cardboard or lightweight, thin and sturdy plastic material, and your engines out of those thick plastic pipes.

It would be very bad if your rocket's parachute fails (or you don't install it, which is often illegal) and an aerodynamic metal pipe is hurling towards the ground. It's a missile, and the speeds involved are insane.

Basically, this.

The sound of such thing is very creepy. It whistles, just like a real missile.

Actually, the overwhelming majority of commercial high-power rocket motors have aluminum casings. You may be confusing them with steel cases, which are basically verboten. However, PVC cases are also viable, and in OP's case may be easier to work with.

Whatever you make the case out of, it is extremely important to make sure the forward and aft closures fail first:

http://www.rocketryforum.com/showthread.php?59573-Experimental-rocket-motor-design-and-construction

Hobby rocketry has standards for cases. Steel and Stainless Steel is not permitted. Hobby rocket cases are made from 6061T6 aluminum or equivalent only because if they fail, they fail in a known, predictable manner without making a lot of shrapnel. All cases must be designed to fail by spitting the forward closures and/or the nozzle as the area above and below the rocket is by definition cleared before ignition. The fore and aft closures should not fail below 2x MEOP, and the cylindrical casing should not fail below 4x MEOP.

If the aft closure or nozzle fails, there are two main cases:

(a) grains stay in motor, but increased nozzle area leads to severely reduced thrust. In general, this is the best-case scenario, but off-axis or slightly too little thrust can result in the rocket flying out of control. If electronic deployment is not used, the rocket may hit the ground before the chute deploys.

( the grains and aft closure are forcibly ejected from the rocket. This may damage the launch pad and the rocket's motor retention system, and acceleration spikes can damage the rocket, or launch it high into the air without electronic chute deployment systems registering a launch. In addition, burning propellant grains on the ground can start fires.

Here's an example of a particularly dangerous aft closure failure which results in the motor casing flying around without a rocket attached (1st flight in video)

And here's a PVC rocket (presumably sugar propellant) blowing its nozzle.

If the forward closure fails, you generally get flames shooting out of both ends of the motor. The exhaust will instantly separate the rocket sections, but the parachute or shock cord may melt, the forward section of the rocket will be barbequed. Again, there is a fire hazard, both from the rocket landing with propellant still burning and from the rocket being set on fire.

Here's an example of a forward closure failure on an H-class motor (and the source of UpsilonAerospace's profile picture):

Here's the same thing on an O-class motor. Note that there's propellant burning after the rocket lands

Now, those look bad, but failures of the main casing are much, much, much worse.