page_title: Synchronization gear
section_title: The Fokker Stangensteuerung gear
hierarchical_section_title: Synchronization gear / History / Fokker's Synchronizer and other German gears / The Fokker Stangensteuerung gear
caption_attribution_description: English: Closeup of a Fokker E.I's Oberursel U.0 seven cylinder rotary engine, and Stangensteuerung synchronizer gear drive cam/rod unit behind engine crankcase.
context_page_description: A synchronization gear, or a gun synchronizer, sometimes rather less accurately called an interrupter, is attached to the armament of a single-engine tractor-configuration aircraft so it can fire through the arc of its spinning propeller without bullets striking the blades. The idea presupposes a fixed armament directed by aiming the aircraft in which it is fitted at the target, rather than aiming the gun independently.
  There are many practical problems, mostly arising from the inherently imprecise nature of an automatic gun's firing, the great velocity of the blades of a spinning propeller, and the very high speed at which any gear synchronizing the two has to operate.
  Design and experimentation with gun synchronization had been underway in France and Germany in 1913–1914, following the ideas of August Euler, who seems to have been the first to suggest mounting a fixed armament firing in the direction of flight. However, the first practical—if far from reliable—gear to enter operational service was that fitted to the Eindecker monoplane fighters, which entered squadron service with the German Air Service in mid-1915.
context_section_description: Whatever its ultimate source, the initial version of the Fokker synchronization gear (see illustration) very closely followed, not Schneider's patent, as claimed by Schneider and others, but Saulnier's. Like the Saulnier patent, Fokker's gear was designed to actively fire the gun rather than interrupt it, and, like the later Vickers-Challenger gear developed for the RFC, it followed Saulnier in taking its primary mechanical drive from the oil pump of a rotary engine.  The "transmission" between the motor and the gun was by a version of Saulnier's reciprocating push-rod. The main difference was that instead of the push rod passing directly from the engine to the gun itself, which would have required a tunnel through the firewall and fuel tank (as shown in the Saulnier patent drawings), it was driven by a shaft joining the oil pump to a small cam at the top of the fuselage. This eventually proved unsatisfactory, as the oil pump's mechanical drive spindle was insufficiently robust to take the extra load. 
  Before the failings of the first form of the gear had become clear, Fokker's team had adapted the new system to the new Parabellum MG14 machine gun, and fitted it to a Fokker M.5K, a type which was at the time serving in small numbers with the Fliegertruppen as the A.III. This aircraft, bearing IdFlieg serial number A.16/15 became the direct forerunner to the five M.5K/MG pre-production prototypes built, and was effectively the prototype of the Fokker E.I – the first production single-seat fighter aircraft armed with a synchronized machine gun. 
  This prototype was demonstrated to IdFlieg by Fokker in person on 19–20 May 1915 at the Döberitz proving ground near Berlin. Leutnant Otto Parschau was test flying this aircraft by 30 May 1915. The five production prototypes (factory designated M.5K/MG and serialed E.1/15 – E.5/15) were undergoing military trials shortly thereafter. These were all armed with the Parabellum gun, synchronized with the first version of the Fokker gear. This prototype gear had such a short life that a redesign was necessary, producing the second, more familiar, production form of the gear.
  The gear used in the production Eindecker fighters (see diagram) replaced the oil pump's mechanical driveshaft-based system with a large cam wheel, almost a light flywheel, driven directly from the spinning rotary engine's crankcase. The push rod now took its reciprocating motion directly from a "follower" on this cam wheel. At the same time the machine gun used was also changed—an lMG 08 machine gun, the so-called "Spandau", replacing the Parabellum used with the prototype gear. At this time the Parabellum was still in very short supply, and all available examples were required as observers' guns, the lighter and handier weapon being far superior in this role.
  The first victory using a synchronized gun-equipped fighter is now believed to have occurred on 1 July 1915 when Leutnant Kurt Wintgens of Feldflieger Abteilung 6b, flying the Parabellum-armed Fokker M.5K/MG aircraft "E.5/15", forced down a French Morane-Saulnier Type L east of Lunéville.
  Exclusive possession of a working gun synchronizer enabled a period of German air superiority on the Western Front known as the Fokker Scourge.  The German high command was protective of the synchronizer system, instructing pilots not to venture over enemy territory in case they were forced down and the secret revealed, but the basic principles involved were already common knowledge, and by the middle of 1916 several Allied synchronizers were already available in quantity.
  By this time, the Fokker Stangensteuerung gear, which had worked reasonably well for synchronizing a single gun, firing at a modest cyclic rate through a two-bladed propeller driven by a rotary engine, was becoming obsolete.
  Stangensteuerung gears for "stationary", i.e.,  in-line engines, worked from a small cam immediately behind the propeller (see illustration). This produced a basic dilemma: A short, fairly robust push rod meant that the machine gun had to be mounted well forward, putting the breech of t
caption: Detail of early Fokker Eindecker – cowl is removed, showing Fokker's original Stangensteuerung gear connected directly to the oil pump drive at the rear of the engine.
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