The Buzz-Bomb or Helicopter are very popular flying fireworks. Both are basically the same device, but the Buzz-Bomb explodes with a loud report at the apex of its flight. Buzz-bombs differ from black powder rockets in that the exhaust from the nozzle is projected sideways, exerting a torque. When lit, hot gasses, sparks and flame shoot out the side of a small 1/8" vent hole located at the bottom of the device making it spin. The helicopter wings attached to the device cause it to lift off the ground into the air with great speed. If you were to make an exhaust hole in the cardboard casing alone without the use of clay, the intense heat and flame would widen the hole in a fraction of a second, reducing the thrust and making the device just flop around on the ground.

Helicopter construction

Composition

Most rocket propellants are suitable, particularly those that produce interesting sparks. The following composition works well.

Materials

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. Parallel wound tubes do not have the spiral seam that goes down the length of the tube (like the tube from a roll of paper towels or toilet paper has).

Tools
A small and a long flat-ended rammer and an unconventional rammer will be needed (One with pointed end). With some patience it can be made by evenly filing down one end of a straight rod. Alternatively, you could drill a lengthwise hole of 5 mm diameter in the center of a flat ended dowel and fix a short length of 5 mm rod in that (much like as is done in the construction of a spindle). What the tooling does is to form a cavity of heat resistant Rocket Nozzle Mix at the bottom of the tube. With the Rocket Nozzle Mix cavity in place, the flame & hot gasses pass through the small vent hole in it, which they cannot burn through, so the hole stays at 1/8" all through the flight.

Clay
The nozzle and end plug are formed from clay, much like as is done in the construction of rockets. As will be described shortly, the nozzle shape is different though. Bentonite, kaolin and ground kitty litter all work well. In this example unground kitty litter coated with Waterglass is used.

Wing
Wings can be purchased from many pyro supply companies, although ordinary popsicles can be used.

Other
You will also need a funnel, scoops, candle (if using popsicle as wing), 1/8mm drill bit and drill and paper tape, superglue or hot melt glue gun,black match or visco fuse and a rubber mallet.

Construction

Temporarily seal one end of each casing with a bit of paper tape.

Put a piece of paper tape on the pointed rammer. Insert it in the casing and draw a line on the paper tape along with the casings edge. This way you will know how thick the clay plug is while ramming. 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. You don't need to use a huge amount of force to achieve a rock hard clay plug. Exerting too much force will split you casing or cause a very small fracture, which under pressure can cause your device to CATO. Once the clay plug is thick enough draw another line on the paper tape.

Line the pointed rammer beside the casing. The second drawn line should be at the edge of the casing. Now draw a line one the casing at the tip of the pointed rammer.

Next you need to add the composition 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 nozzle, using a powder scoop for adding the composition can help produce consistent results at this point. If you add too much composition you can create small air pockets in the composition and this will affect the performance. Finally, ram a layer of clay again to form an end plug. The end plug of the device should be the same thickness as the casings inner diameter

A exhaust vent hole now needs to be drilled into the side of the tube a few millimetres over the line. The hole needs to be drilled 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 necessary speed to lift the device off the ground. As depicted, carefully drill the exhaust in the side of the casing, into the clay plug and finish when you have reached the propellant composition.

Skip this part if you have bought your wings from a pyro supply. Light your candle and carefully bend the popsicle in the middle over the flame. Use your right hand to turn the right side of the wing against yourself and vice versa. Of course you should only do this a long distance from compositons and ready-made devices.

Since the propeller must be at an exact angle, an angle-finder can be used. It is simply 2-3 pieces of cardboard glued together. A 135 degree angle is drawn on the cardboard. Then a hole, which diameter is equal to the casings O.D., is drilled in the centre. Mark with 'Hole' and 'Propeller'

To find the angle, place the angle-finder on the ground and isert you casing. Look from above with one eye closed and adjust the casing, so the vent hole is right beside 'Hole.' Now draw a point on your casing beside 'Propeller.'

Glue the wing to the propeller point with some super glue or hot melt glue. If the glue is not strong enough, a few straps of cotton or hemp twine around the propeller may help.

This is optional, but highly recommended. Put a few drops of waterglass around the vent hole with an eyedropper or a disposable pipette. The waterglass makes the vent more impervious to hot exhaust gasses. Let the waterglass dry for about 20 minutes.

Insert the visco fuse in the vent hole and secure with hot melt glue or paper tape. The picture on right shows how the vent should be related to the propeller. If the vent hole is on the wrong side, the helicopter will not fly upwards unless you fire it upside down.

Place on the ground with the casing resting on the ground and the wing on top. Light fuse and get away. Keep well away from these items. They are somewhat unpredictable and may bounce around on the ground instead of climbing into the air. Like rockets, they may explode if the propellant is not compressed well. The end plug or nozzle may also be blown out which can be hazardous.

Video below shows these DIY helicopters in action: