cessful wheel as they provide the thrust which turns the wheel. A driver is very simi- lar to a rocket, the main difference being that a driver is end-burning while a rocket burns from the center out. End-burning keeps the surface area of the propellant constant throughout the duration of the burn, provid- ing an even thrust as opposed to the violent start and diminishing strength of a rocket. A good driver must have a sturdy casing, pref- erably a convolute Kraft paper tube. A good standard size for a driver is 1/2" inside diame- ter by 6" long, with a minimum wall of 1/8".
The first step in constructing a driver is to ram a sturdy clay choke into one end of the tube. I prefer to space the choke approxi- mately 3/16" from the end of the tube. I do this by placing the tube over a base con- structed with a 3/16" x 1/2" protrusion (see illustration A). The choke is spaced 3/16" from the end of the tube in order to prevent it from being easily expelled. Upon ramming, the tube expands at the choke, preventing the choke from passing through the end of the tube which retains the original 1/2" diame- ter. Granular bentonite clay makes an excel- lent choke, as does fire clay. I place the loading base on a solid surface and with a 1/2" rod, "loading drift" (preferably aluminum or brass), I hand ram the choke approximately 75% of the diameter of the tube. I pound the drift with a mallet until the choke is hard- packed and expands the tube slightly. The container in which the clay is kept should be left open so that the clay can absorb mois- ture from the air. This slight amount of moisture is all that is required to bind the clay together. Once it h a s been determined the adequate number of blows to pack the clay hard, that number should be used to pack the clay in any other drivers that are made.
The next step in constructing a driver is to load the fuel. Fuel should be loaded in in- crements which do not exceed, when packed, one diameter of the tube. All increments of fuel should be the same and small enough to prevent erratic burning. The same number of
blows used for packing the choke should be used to load each increment of fuel. The very first load of fuel should consist of straight Black Powder to avoid the possibility of sparking when the driver is drilled. Enough fuel should be loaded to allow for a 6 - 7 sec- ond burn duration.
Among the many possible fuels, I will discuss three basic effects widely used in drivers. The first effect is the charcoal driver, which is simply a Black Powder fuel with the addition of coarse charcoal. This continues burning after being expelled from the nozzle, giving a soft charcoal scintillation. The second is the steel/cast iron effect. This, again, is a Black Powder base with the addition of steel or cast iron filings. I use 16 mesh size. This creates a stream of golden sparks similar to that which is produced by a cutting torch. Third is the titanium driver, which again is Black Powder based with the addition of titanium flakes/grains. Different size particles produce different effects. Finer particles produce a thick cloud of silver sparks close to the driver, while coarser particles will produce a much longer, less dense trail of silver.
After the fuel is loaded, a nozzle must be created by properly drilling the choke. My drivers are typically drilled 9/64", a size de- termined purely by trial and error - experi- ence! If the choke is drilled too small, the driver will explode or expel the choke; if drilled too large, the desired thrust will not be achieved. The base I use h a s a small pro- trusion in the center which provides a guide for drilling. Drivers should be drilled com- pletely through the clay choke. A small amount of fuel should then be packed into the drilled hole. This prevents the possibility of explosions due to increased surface burn area.
Priming is the next step. I prime my drivers with a nitrocellulose meal prime thinned with acetone. Proportions of meal powder and NC are usually not specific. I try to use as much meal powder as possible, but it must remain firm when dry. Using a plastic squeeze-type ketchup bottle, I thin the prime with acetone
DRIVER FORMULAS
CAST IRON 80% - Meal D 20%-16 mesh cast iron (or steel)
TITANIUM 93.5% - Meal D 6.5% - titanium, 16-40 mesh sponge or flake
CHARCOAL 90% - Meal D 5% -charcoal, 36-80 mesh 5% - lampblack 75.3% 18.3% 6.3% CAST IRON 25 - Meal D
6 - homemade Black Pow- der
2 - steel 16 mesh or cast iron
TITANIUM
25 - Meal D
6 - homemade Black Powder 2 - titanium -10 to +40 mesh sponge NOTES Meal D Homemade Black Powder Cast Iron
GOEX commercial Meal powder 75/15/10 ball milled
Brake turnings -16mesh. Must be treated with wax or oil if stored for any length of time
to the consistency of maple syrup. In use, I squeeze enough prime into the choked end to cover the clay, and then place a small piece of match into the center of the nozzle through the moist prime. It dries overnight.
The final step in driver construction is nos- ing, which provides a means of connecting piped match or fuse to the driver for ignition or transfer of fire. Typical nosing consists of 30 lb. Kraft paper rolled three turns around the tube, with two inches extending beyond each end. A small dab of paste is applied to the tube as I begin rolling, and the final turn is secured by a 1/2" strip of wheat paste or glue applied to the edge of the paper. GD
BASE
1/2" DRIVER Illustration A