Hummer

[edit] Materials

Click for larger image

Casing
A paper tube is used as a casing. Under no circumstances be tempted to use materials other than paper. It is dangerous and unnecessary. Roll or buy thick walled cardboard tubes, preferably parallel wound as they are much stronger than spiral wound tubes. It is imporant the walls of the tube are thick because the exhaust hole on the side of the hummer will burn a large hole very fast in a thin walled tube.

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 a funnel, 2 mm drill bit and drill and paper tape, black match or visco fuse.

Propellant
Simple black powder (Meal - Black powder) in the standard ratio (75:15:10) works well to spin the hummer. You can also create interesting spark effects if you add some additional metal powders (like aluminium, titanium or magnesium) to the black powder. However this may alter the burn rate of the mixture slightly, perhaps requiring you to adjust the dimensions of the exhaust hole.

[edit] Construction

Click for larger image

The casing in this example is 30mm long and has an inner diamter of 10mm. The casing wall is about 4mm thick and normally this would be too thin, however it is re-enfored with waterglass (sodium silicate) which prevents the exhaust from buring into a big hole. Temporarily seal one end of the casing with a bit of paper tape.

Click for larger image

Take a small amount of nozzle mix and dump this into the casing, tapping it to settle the powder. The aim is to approximately make the end plug the same thickness of the casings inner diameter. This can be a little tricky and is an important step, an end plug that is too thin will not be able to withstand the inner pressure and blow off. To be consistent make some tooling like a powder scoop to measure exactly the same amount every time. That way you are guaranteed accurate results.

Click for larger image

Insert the ram into the inner casing and gently ram it with your hammer. You don't need to use a huge amount of force to achieve a rock hard end plug. Exerting too much force will split you casing or cause a very small fracture, which under pressure can cause your hummer to CATO.

Click for larger image

Next you need to add the meal powder in small increments (as always, no more at a time than will give a layer after ramming as thick as the casings inner diameter). As with the end plug, using a powder scoop for adding the meal powder can help produce consistent results at this point. If you add too much meal powder you can create small air pockets in the composition and this may again cause the hummer to CATO. Finally, ram a layer of clay again to form an end plug.

Click for larger image

This next step is very important in making your hummer work. You need to drill a hole in the side of the casing on such an angle that it will make your casing spin at very high revolutions. If you get the angle wrong then your casing will not generate the nessessary speed to make a loud humming sound. As depicted, carefully drill the exhaust in the size of the casing about half way along the length of the tube. The angle in which the hole needs to be drilled is the same as in the picture.

Click for larger image

It is recommended that you place a small amount of waterglass around the exhaust hole to prevent it buring into a larger hole. If the hole is allowed to expand the hummer will either loose speed and/or the angle of the exhaust hole will be altered turning the hummer into a bad rocket. Once the waterglass has dried insert a black match or visco fuse into the hole. If the fuse is loose, to prevent it from falling out it may be secured with a small amount of prime.