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The Vickers-Challenger gear
The first British synchronizer gear was built by the manufacturer of the machine-gun for which it was designed: it went into production in December 1915. George Challenger, the designer, was at the time an engineer at Vickers'. In principle it closely resembled the first form of the Fokker gear, although this was not because it was a copy (as is sometimes reported): it was not until April 1916 that a captured Fokker was available for technical analysis. The fact is that both gears were based closely on the Saulnier patent. The first version was driven by a reduction gear attached to a rotary engine oil pump spindle, as in Saulnier's design; a small impulse-generating cam was mounted externally, on the port side of the forward fuselage, where it was readily accessible for adjustment.[52]
Unfortunately, when the gear was fitted to types such as the Bristol Scout and the Sopwith 1½ Strutter, which had rotary engines and their forward-firing machine gun in front of the cockpit, the long push rod linking the gear to the gun had to be mounted at an awkward angle, in which it was liable to twisting and deformation (not to mention expansion and contraction due to temperature changes).
Much neater, more practical application of the Vickers-Challenger gear for the synchronized Vickers gun of an R.E.8.
For this reason the B.E.12 and the R.E.8, not to mention Vickers' own FB 19, mounted their forward-firing machine guns on the port side of the fuselage so that a relatively short version of the push rod could be linked directly to the gun.
This worked reasonably well, although the "awkward" position of the gun, which precluded direct sighting, was initially much criticised. It proved less of a problem than was at first supposed once it was realized that it was the aircraft that was aimed rather than the gun itself. The last aircraft type to be fitted with the Vickers-Challenger gear, the R.E.8, retained the port-side position of the gun even after most R.E.8s were retrofitted with the C.C. gear from mid 1917.
The Scarff-Dibovski gear
Lieutenant Victor Dibovski, 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,[53] although it is possible that the earlier Dibovski gear was actually a deflector system rather than a true synchronizer.
Cam gear of the Scarff Dibovsky
In any case, Warrant Officer F. W. Scarff worked with Dibovski 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.[54]