SHOOTING THROUGH THE PROPELLER
Now, the fleetest machines and the most easily manœuvered are those of the tractor type, that is, the ones which have the propeller in front; but having the propeller in front is a handicap for a single-seater machine, for the gun has to be fired through the propeller and the bullets are sure to hit the propeller-blades. Nevertheless the French did fire right through the propeller, regardless of whether or not the blades were hit; but at the point where they came in line with the fire of the gun they were armored with steel, so that there was no danger of their being cut by the bullets. It was calculated that not more than one bullet in eighteen would strike the propeller-blade and be deflected from its course, which was a very trifling loss; nevertheless, it was a loss, and on this account a mechanism was devised which would time the operations of the machine-gun so that the shots would come only when the propeller-blades were clear of the line of fire.
Machine-Gun mounted to Fire over the Blades of the Propeller
Courtesy of "Scientific American"
Mechanism for Firing Between the Blades of the Propeller
The cam B on the propeller shaft lifts the rod C, rocking the angle lever D which moves the rod E and operates the firing-piece F. Firing may be stopped by means of lever H and Bowden wire G. I is the ejection-tube for empty cartridges.
It would take a Hundred Horses to Supply the Power for a Small Airplane
A cam placed on the propeller-shaft worked the trigger of the machine-gun. This did not slow up the fire of the machine-gun. Quite the contrary. We are apt to think of the fire of the machine-guns as very rapid, but they usually fire only about five hundred rounds per minute, while an airplane propeller will make something like twelve hundred revolutions per minute. And so the mechanism was arranged to pull the trigger only once for every two revolutions of the propeller.