A synchronizer or interrupter gear is a device operating between the machine gun and engine of an airplane, which causes the gun to be fired at the proper moment so that the bullets wll not strike the revolving propeller. Only fixed guns can be synchronized. Originally, fixed gauns, were timed to fire between the blades of the propeller by a device which interrupted the gun at the moment the blade passed the muzzle of the gun. However, this was found to be very unsatisfactory, owing to the construction of the gun, and it was found that a much more satisfactory operation could be obtained by having a gear fire the gun at certain points throughout the revolution of the propeller when the blade was not opposite the muzzle of the gun.

There are two kinds of synchronizer or interrupter gears:

1. Mechanical.

2. Hydraulic or C. C.

The mechanical gear is a system of rods actuated by cams on the engine which are timed to fire the gun at the proper moment.

The hydraulic, or C. C. type of gear consists of a system of copper tubes filled with oil under high pressure. A cam on the engine generates an impulse at one end of the tube which is conveyed through the column of oil to the trigger motor of the machine gun, causing it to fire at the proper moment.

Great care must be taken with all synchronizing devices to see that the cam is timed to fire the gun at the proper instant. The gun should shoot just as the trailing edge of the propeller passes the muzzle of the gun.

Proper synchronizing can be carried out only on machine guns having a single shot trigger; that is, a trigger, which when pressed will permit of only one shot being fired until released an pressed again.

The Malin, Browning, and Vickers guns have been fitted with single-shot triggers and successfully synchronized - but the Lewis has not as yet been satisfactorily adapted as a fixed gun.

The mechanical gear necessitates less care than the hydraulic type, as it is only necessary to keep it oiled and troperly timed. It is possible that in the near future hydraulic gears will be discarded in favor of the mechanical.

The hydraulic type must be constantly inspected for leaks; and if air bubbles form in the tube the timing is apt to be seriously affected, resulting in the shots striking the propeller.

After long flights the synchronizing gear cams should be carefully inspected for wear, and the gun should be retimed.



HYDRAULIC OR C. C. SYNCHRONIZING GEAR

The hydraulic synchronizing gear, commonly known as the C. C. interrupter gear, is named after the inventor, Mr. Constantinesco. The following principal parts are embodied in this gear:

1. Reservoir.

2. Generator - furnished with engine by engine manufacturers.

3. Trizzer motor.

4. Control lever.

5. Pipe system.

The reservoir is connected to the generator on the engine by a copper tube of small diameter, about one-sixteenth inch. A larger tube, three-eighths inch diameter, runs from the generator to the trigger motor on the gun. The cam in the generator, is arranged so that it raises the plunger in the generator to its highest point just as the trailing ge of the propeller passes the muzzle of the gun.


ACTION

The piston in the reservoir is withdrawn to its farthest point, thereby placing the oil in the reservoir under high pressure. A wire from the control lever connects with a valve at the lower end of the reservoir and opens this valve when the lever is pulled. This causes the high pressure to travel along the tube to the generator and forces the plunger down on the cam. The rise on the cam lifts the plunger, and in so doing imparts an impulse to the oil which travels along the line of least resistance in the larger tube, and presses the plunger in the trigger motor, thereby firing the gun.

Tge great advantage of this type of gear is that it is so easily adapted to any type of engine or airplane owing to the fact that the copper tubes can be bent around any obstacle and placed wherever convenient. Owing to the steel rods, etc., of the mechanical gear, this flexibility can not be obtained and the gear has to be specially designed for each type of engine and airplane to which it is to be adapted.



MECHANICAL SYNCHRONIZING GEAR - TYPE HS

The mechanical sycchronizing gear type HS is designed for use in connection with the Hispano Suiza engine, having been in use for some time on the French Spad, and now adapted for the Curtiss JN4-HG training plane.

Either one or two guns may be synchronized with this engine, as it will accommodate two of the type HS gears, one attached to either cam shaft.


DESCRIPTION

The gear consists of a circular 4-point cam fastened to the end of the engine cam shaft. A push pin bearing against the cam actuates a rod, which in turn actuates annother rod fastened above the gun and bearint against the trigger.

The firing of the gun is controlled by a Bowden wire lever attached to the control stick of the airplane. When the control lever is pulled, a tappet is attache in line with the push pin and the rods are actuated, tereby firing the gun.