Editing Synchronization gear (section)

== Nomenclature ==
A mechanism to enable an automatic weapon to fire between the blades of a whirling propeller is usually called an interrupter or synchronizer gear. Both these terms are more or less misleading, at least insofar as explaining what happens when the gear functions.<ref name=Woodman1>Woodman 1989, pp. 171–172.</ref>

The term "interrupter" implies that the gear pauses, or "interrupts" the fire of the gun at the point where one of the blades of the propeller passes in front of its muzzle. Even the relatively slowly revolving propellers of First World War aircraft, however, typically turned twice or even three times for each shot a contemporary machine gun could fire. A two-bladed propeller would therefore obstruct the gun six times every firing cycle of the gun, a four-bladed one twelve times. A gun set up this way would be interrupted more than forty times per second,<ref name=Hegener1>Hegener 1961, p. 26.</ref> while firing at only around seven rounds per second. Unsurprisingly, the designers of so-called interrupter gears found this too problematic to be seriously attempted, as the gaps between "interruptions" would have been too short to allow the gun to fire at all.<ref name=Volker2p80-81>Volker 1992, pt. 2, pp. 80–81.</ref>

True synchronization, though, with a machine gun's rate of fire exactly proportional to the revolutions per minute of a spinning aircraft propeller, would require an impractical level of complexity.<ref name=Mixter1>Mixter and Edmonds 1919, p. 2.</ref> A machine gun normally fires a constant number of rounds a minute, and while this may be changed by modifying the gun, it cannot be varied at will while the gun is operating. The rate of rotation of an aircraft propeller, meanwhile, especially before the advent of the [[constant-speed propeller]], could vary widely, depending on the throttle setting and what maneuvers were being performed. Even if it had been feasible to pick a particular point on an aircraft engine's tachometer at which a machine gun's cyclic rate would permit it to fire through the propeller arc, this would be very limiting.<ref name=Kosin3>Kosin 1988, pp. 18–19.</ref>

It has been pointed out that any mechanism that achieved the feat of firing between the whirling blades of a propeller without striking them could be described as "interrupting" the fire of the gun (to the extent that it no longer actually works as an automatic weapon at all), and also as "synchronizing", or "timing" its fire to coincide with the revolutions of the propeller.<ref name=Woodman2>Woodman 1989, p. 172.</ref>