Cam gear of the Scarff Dybovsky
Lieutenant Victor Dybovski, an officer of the Imperial Russian Navy, while serving as a member of a mission to England to observe and report on British aircraft production methods, suggested a synchronization gear of his own design. According to Russian sources, this gear had already been tested in Russia, with mixed results, although it is possible that the earlier Dybovski gear was actually a deflector system rather than a true synchronizer.
In any case, Warrant Officer F. W. Scarff worked with Dybovski to develop and realize the gear, which worked on the familiar cam and rider principle, the connection to the gun being by the usual push rod and a rather complicated series of levers. It was geared in order to slow the rate that firing impulses were delivered to the gun (and hence improve reliability, although not the rate of fire).
The gear was ordered for the Royal Naval Air Service and followed the Vickers-Challenger gear into production by a matter of weeks. It was more adaptable to rotary engines than the Vickers-Challenger, but apart from early Sopwith 1½ Strutters built to RNAS orders in 1916, and possibly some early Sopwith Pups, no actual applications seem to have been recorded, and no patent was ever taken out.
The Imperial Russian Air Service, in common with other World War I air services, struggled to find a way of allowing a machine gun to fire safely through the spinning propeller of an airplane. The Russian High Command was tardy in realizing the necessity for arming its aircraft throughout 1914 and 1915, leaving frustrated aviators using such impromptu armaments as pistols, rifles, trolled anchors and cables, and other makeshifts. Part of the delay was caused by a paucity of light automatic weapons that an aircraft could lift. However, it became apparent that the ability to aim both gun and aircraft simultaneously was a great advantage in aerial combat.
In late 1915, Naval Lieutenant Victor Dybovsky of the 20th KAO invented a system of cam plates mounted on an engine's crankshaft that would prevent a machine gun from holing an airplane's propeller. Static tests at the Lux Aircraft Works proved its feasibility by November 1915; towards the end of the month, Morane-Saulnier G serial no. MS567 was forwarded to the 30th KAO for field testing. Poruchik Mikhail Shadsky flew test flights on both 9 and 29 December; cold thickened the machine gun's lubricant both times, preventing it from firing.
When testing restarted in April 1916, Shadsky had more success. During April and May, he engaged the enemy about ten times. He shot down Austro-Hungarian airplanes on both 23 and 24 May 1916, but crashed to his death and the plane's destruction after the latter encounter. However, production of the interrupter gear was never carried out. Instead, Dybovsky was posted to England to inspect aircraft being constructed by the Royal Flying Corps. He sold his patent to the British; it became the Scarff-Dybovxky system used by the British. Thus it was that by April 1917, Russian had only a couple of dozen fighter planes with synchronized guns.
In the interim, Praporshchik Victor Kulebakin was installing cam deflectors on another Morane-Saulnier's crankshaft. Testing in July 1917 showed that the deflectors did indeed pop out from under the aircraft's cowling to deflect any bullets that threatened the propeller. Although the modification was simple enough it could be fabricated in a unit's workshops, it was not widely used.