“Give a person fireworks, and you make them happy for a day.
Teach a person how to make fireworks,
And you make them happy for a lifetime.”
There are three common types of simple, black powder, charcoal-tailed, rocket motors: cored, nozzleless, and end-burner.
A cored black powder rocket motor is the traditional motor, typically with a clay nozzle, and a hollow core going up through the nozzle and into the fuel grain for some distance. This is how the typical sky rocket is constructed. If you take the nosing off the bottom of a commercial sky rocket and look up into the end of it, you’ll see about a half inch tall ring of clay, which forms the nozzle, and then a longer core going up into the black fuel grain.
A nozzleless motor is a fairly recent development as far as I know, and it has no clay nozzle, but does still have the core going up into the fuel grain. It uses a hotter fuel than the cored rocket motor.
An end-burning motor has a clay nozzle, but no core going up into the fuel grain. The fuel burns only from its end, and this type of motor typically uses a hot fuel and has a smaller hole, or aperture, in the clay nozzle than does a cored motor. Often, full strength 75/15/10 (potassium nitrate, charcoal, sulfur) black powder is used as the fuel in these motors, and typically the diameter of the nozzle aperture is one quarter of the inside diameter of the motor tube (3/16″ nozzle aperture for a 3/4″ ID rocket tube).
It is this latter type of motor, the end-burner, which I intend to use to test the power of fuels made with 5 different charcoals in an upcoming article, Some Notes on Experiments with Various Charcoals.
The nice thing about these motors is that they burn for a fairly long time, up to about 10 seconds, with a constant amount of thrust. That thrust varies considerably from one charcoal to another, in my past experiences.
Below is a shot of a motor that I carefully sliced in half with a hacksaw, outdoors. You can see how solidly the fuel packs when dampened just a bit, with no separation between fuel increments. You can also see how the top of the nozzle is shaped to direct the flow of the burning gasses smoothly out of the hole.
End burning motors are useful for more than just rockets, though. They can be used as short duration gerbs (fountains, pronounced like the first part of “gerbil”), or as drivers on wheels or girandolas (horizontal flying wheels). When I want metal sparks in the motor’s exhaust, I add 6% fine ferro-titanium or spherical titanium powder to this homemade rocket fuel.
The methods for making end-burner rocket motors are very similar to the ones for making regular gerbs and less powerful wheel drivers. Those devices typically are made on a larger diameter spindle, and their fuels are less powerful than the rocket motors.