Nozzleless bottle rocket

From PyroGuide

A nozzleless bottle rocket is simply a small black powder rocket without a nozzle.

[edit] Materials

Casing A paper tube is used as a casing, about 1" to 1.5" in length and about 1/4" to 1/2" in diameter. Under no circumstances be tempted to use materials other than paper. It is dangerous and unnecessary. Find, roll or buy thick walled cardboard tubes, preferably parallel wound as they are much stronger than spiral wound tubes. The tubes should be sufficiently strong to allow ramming without wrinkling and to withstand the internal pressure during flight, but not to heavy to decrease performance.

Tools A rammer and a hammer are needed. Non sparking materials, such as aluminium, brass, rubber and wood should be used. You will also need paper tape and a scoop for your various powders.

Propellant Simple lifting charge in the standard ratio (74:14:12) works well to propel the rocket, but is somewhat boring in that it does not produce any interesting effects. Therefore, you may want to add some metal powders (2%...5%) to obtain an interesting spark tail. This may alter the burn rate of the mixture slightly, perhaps requiring you to adjust the dimensions of the core.

Endcap Bentonite and kaolin clay work well (better for payload) or thick cardboard\card stock glued or taped in place (better for smaller, payload-less rockets). The dry clay powder is rammed into the casing, producing a solid plug. Cheap kitty litter is often made of bentonite clay and may be used instead. Grind up the kitty litter into a fine powder, which is most easily done with a ball mill or coffee grinder.

[edit] Construction

If you are sealing the tube with thick cardboard\card stock then you can skip the first step.

Temporarily seal one end of the casing with a bit of paper tape. Take a small amount of Bentonite clay and dump this into the casing, tapping it to settle the powder. The aim is to make the end cap approximately half the thickness of the casings inner diameter. (Ex: A 1/2" diameter tube would have a 1/4" end plug). Insert the ram into the inner casing and gently ram it with your mallet. You don't need to use a decent amount of force to achieve a rock hard end cap..

Next you need to add the charge in small increments (as always, no more at a time than will give a layer after ramming as thick as the casings inner diameter). Using a powder scoop for adding the meal powder can help produce consistent results at this point.

Finally, drill a 2-4mm (about 3/32") hole about 8/10ths of the way down the middle of the propellant for the core. The core is vital, as it allows the sufficient thrust to be generated to lift the rocker into the air.

All that remains is a fuse to light and a stick to stabilise the rocket. Use a straight stick for this (see rocket stabilization below). It can be attached with hot glue or paper tape. A sufficiently long (don't economise on fuse!) length of fuse is inserted into the core of the rocket, as far as it goes. Black match or visco fuse may be used. The fuse may be bent over and held in place with paper tape on the side of the rocket. This way of fusing allows you to light the rocket without having to hold a flame directly under the lift charge. Remember, never stand over the rocket when lighting.

[edit] Rocket Stabilization

Now that you have built your rocket, it needs to be stabilized during it's flight time (in other words it needs to fly vertically). This control of your rocket is essential, not only for the safety of you or your audience but for your satisfaction. Especially if you have a payload attached, this needs to explode high in the sky and not on or near ground level. At all times we want to avoid injury or possibly starting a fire.

Stabilizing your rocket is relatively a simple process as long as you follow these rules. Your stick needs to be straight and it needs to be long and heavy enough to pass the balance test. This test is simple, attach a stick to the side of your finished rocket and try and balance your rocket on your finger. Do this by placing your finger just behind the exhaust nozzle. If the rocket topples forward, then your stick is not long or heavy enough and may cause it to fly in unpredictable directions. If it topples backwards then your stick is too long or heavy and will make your rocket sluggish and reduce it's apogee. If it's too long simply trim a small amount off and do the test again. If it's not long or heavy enough replace the stick with a larger one. Also, if you have for example 2 sticks, which both pass through the balance test, but one is longer and lighter and the other one is shorter and heavier, it's the best to pick the longer lighter stick, so that you rocket will fly better.

Basically the end result you are after is a rocket and stick that balance nicely on your finger when it is placed behind the nozzle. It's a simple process that will ensure your rocket will fly straight into the night sky and join the stars.