Editing Synchronization gear (section)

=== Fokker's Synchronizer and other German gears ===
[[File:Fokker synchdisc.jpg|thumb|upright|left|Fokker Synchronization gear set up for ground firing test. The wooden disc records the point on the disc of the propeller where each round passed. The diagram opposite shows the probable result for a properly working gear. Inherent inaccuracies in both the gear and the triggering of the gun itself, small faults in normal service ammunition, and even the differing RPM rates of the engine, all combine to produce a "spread" of hits, rather than every bullet striking the disc in precisely the same spot]]
[[File:Synchronised gun - working well.svg|thumb|180px|Correctly functioning synchronisation gear: all rounds fired well within "safe" zone (well clear of propeller)]]
Inspection of the propeller from Garros' machine prompted Idflieg to attempt to copy it. Initial trials indicated that the deflector wedges would not be sufficiently strong to cope with the standard steel-jacketed German ammunition, and representatives from Fokker and Pfalz, two companies already building Morane copies (although, strangely, not Schneider's LVG concern) were invited to Döberitz to inspect the mechanism and suggest ways that its action might be duplicated.<ref name=Woodman5>Woodman 1989, p. 180.</ref>

[[Anthony Fokker]] was able to persuade Idflieg to arrange the loan of a Parabellum machine gun and ammunition so that ''his'' device could be tested, and for these items to be transported forthwith to the ''Fokker Flugzeugwerke GmbH'' at [[Schwerin]] (although probably ''not'' in his railway compartment or "under his arm", as he claimed after the war).<ref name=Gould1>Fokker, Anthony and Bruce Gould 1931</ref>

The story of his conception, development and installation of the Fokker synchronization device in a period of 48 hours (first found in an authorised biography of Fokker written in 1929) is not now believed to be factual.<ref name=Weyl1>Weyl 1965, p. 96.</ref> Another possible explanation is that Garros's Morane, partly destroyed by fire as it was, had sufficient traces of the original synchronization gear remaining for Fokker to have guessed how it worked.<ref name=Courtney1>Courtney 1972, p. 80.</ref> For various reasons this also seems unlikely,<ref group="Note">The main problem is that it assumes Garros was flying the same machine that Saulnier had used for his earlier tests!</ref> and the current historical consensus points to a synchronization device having been in development by Fokker's team (including engineer [[Heinrich Lübbe]]) prior to the capture of Garros's machine.<ref name=Woodman6/>

==== The Fokker ''Stangensteuerung'' gear ====
[[File:Fok E I's U-0 & Stangensteuerung.jpg|thumb|right|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]]
{{Multiple image
|direction=vertical
|image1 = Toggle Trigger Enabler on Propeller Aircraft with Machine Guns.gif
  |caption1 = The pilot first pushes a trigger enabler, which enables the cam follower.
|image2 = Toggle Trigger Lever on Propeller Aircraft with Machine Guns.gif
  |caption2 = The pilot can then push the trigger lever to fire the machine gun while staying synchronized with the propeller.
|footer = Different parts of the gear are color-coded as follows:
{{legend|#0FDACE|Trigger enabler}}
{{legend|#BD00FF|Trigger lever}}
{{legend|#269EE1|Gun trigger}}
{{legend|#EB4040|Coupling piece}}
{{legend|#34B641|Push rod}}
{{legend|#AC97AB|Cam follower}}
{{legend|#808563|Cam & shaft (shown in both front view and lateral view)}}
}}

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,<ref group="Note">In 1916 LVG and Schneider [[lawsuit|sued]] Fokker for [[patent infringement]]{{snd}}and though the courts repeatedly found in Schneider's favour, Fokker refused to pay any royalties, all the way to the time of the Third Reich in 1933.</ref> 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.<ref name=Woodman7>Woodman 1989, p. 183.</ref> 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.<ref name=Woodman7 />

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, [[Otto Parschau#The Green Machine (A.16/15)|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.<ref name=Grosz2>Grosz 2002, p. 9.</ref>

This prototype was demonstrated to IdFlieg by Fokker in person on 19–20 May 1915 at the [[Dallgow-Döberitz|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<ref name=Grosz2>Grosz 2002, p. 9.</ref>) 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 [[Fokker Eindecker fighters|Eindecker]] fighters replaced the oil pump's mechanical driveshaft-based system with a large cam wheel, almost a light flywheel, driven directly from the [[Rotary engine|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{{snd}}an [[MG 08#Aircraft versions|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]].<ref name=VanWyngarden12>VanWyngarden 2006, p. 12.</ref>

Exclusive possession of a working gun synchronizer enabled a period of German air superiority on the [[Western Front (World War I)|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,<ref name=Courtney2>Courtney 1972, p. 82.</ref><ref group="Note">Courtney rather pungently remarks that "...&nbsp;there was no particular secret to protect".</ref> and by the middle of 1916 several Allied synchronizers were already available in quantity.

[[File:Forward placed synchronised gun.jpg|thumb|left|''Stangensteuerung'' synchronized machine gun mounted well forward on Albatros C.III]]

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 the gun out of the pilot's reach for clearing jams. If the gun was mounted in the ideal position, within easy reach of the pilot, a much longer push rod was required, which tended to bend and break.

The other problem was that the ''Stangensteuerung'' never worked well with more than one gun. [[Fokker E.IV#Design and development|Two (or even three) guns]], mounted side by side ''and firing simultaneously'', would have produced a wide spread of fire that would have been impossible to match with the "safe zone" between the whirling propeller blades. Fokker's initial answer to this was the fitting of extra "followers" to the ''Stangensteuerung's'' large cam wheel, to (theoretically) produce the "ripple" salvo necessary to ensure that the guns were aimed at the same point on the propeller disc. This proved a disastrously unstable arrangement in the case of three guns, and was rather less than satisfactory, even for two.<ref name=Grosz1>Grosz 1996, p. 1.</ref> Most of the early Fokker and Halberstadt biplane fighters were limited to a single gun for this reason.<ref group="Note">At least as much as the more commonly cited effect on performance of the weight of an extra gun.</ref>

In fact, the builders of the new Albatros twin-gunned stationary-engine fighters of late 1916 had to introduce their own synchronization gear, known as the ''Hedtke gear'' or ''Hedtkesteuerung'', and it was evident that Fokker were going to have to come up with something radically new.<ref name=Woodman7 />

==== The Fokker ''Zentralsteuerung'' gear ====
[[File:Zentralsteuerung01.jpg|thumb|Twin guns synchronized by the ''Zentralsteuerung'' system in a [[Fokker D.VIII]] fighter. The "pipes" connecting the guns and the engine are flexible drive shafts]]

This was designed in late 1916 and took the form of a new synchronization gear without any rods at all. The cam that generated the firing impulses was moved from the engine to the gun; the trigger motor in effect now generated its own firing impulses. The linkage between the propeller and the gun now consisted of a flexible drive shaft directly connecting the end of the engine camshaft to the trigger motor of the gun.<ref name=Hegener2>Hegener 1961, p. 32.</ref> The firing button for the gun simply engaged a clutch at the engine which set the flexible drive (and thus the trigger motor) in motion. In some ways this brought the new gear closer to the [[Synchronization gear#The Franz Schneider patent (1913–1914)|original Schneider patent (q.v.)]].

A major advantage was that the adjustment (to set where on the propeller's disc each bullet was to impact) was now in the gun itself. This meant that each gun was adjusted separately, an important feature, since twin synchronized guns were not set to be fired in strict unison, but when they were pointing at the same point on the propeller disc. Each gun could be fired independently, since it had its own flexible drive, linked to the engine camshaft by a junction box, and having its own clutch. This provision of a quite separate set of components for each gun also meant that a failure in the gear for one gun did not impinge on the other.

This gear was available in numbers by mid 1917, in time for installation on the [[Fokker Dr.I]] triplane and all later German fighters. In fact it became the standard synchronizer for the Luftstreitkräfte for the remainder of the war,<ref name=Hegener3>Hegener 1961, p. 33.</ref> although experiments to find an even more reliable gear continued.<ref name=Woodman7/>

==== Other German synchronizers ====
[[File:LVG E I right.png|thumb|[[LVG E.I]], with Schneider ring and forward-firing synchronized gun, presumably with a Schneider-designed gear, about which nothing is now known]]

===== The 1915 Schneider gear =====
In June 1915 a two-seater monoplane designed by Schneider for the LVG Company was sent to the front for evaluation. Its observer was armed with the new Schneider gun ring that was becoming standard on all German two-seaters: the pilot was apparently armed with a fixed synchronized machine gun.<ref name=Cheesman2>Cheesman 1960, p. 177.</ref> The aircraft crashed on its way to the front and nothing more was heard of it, or its synchronization gear, although it was presumably based on Schneider's own patent.<ref name=Woodman8/>

===== The Albatros gears =====
The new Albatros fighters of late 1916 were fitted with twin guns synchronized with the ''Albatros-Hedtke Steuerung'' gear, which was designed by Albatros ''Werkmeister'' Hedtke.<ref name=Volker6p33>Volker 1992, pt. 6, p. 33.</ref> The system was specifically intended to overcome the problems that had arisen in applying the Fokker ''Stangensteuerung'' gear to in-line engines and twin gun installations, and was a variation of the rigid push-rod system, driven from the rear of the crankshaft of the [[Mercedes D.III]] engine.

The [[Albatros D.V]] used a new gear, designed by ''Werkmeister'' Semmler: (the ''Albatros-Semmler Steuerung''). It was basically an improved version of the Hedtke gear.<ref name=Volker6p33/>

An official order, signed on 24 July 1917 standardised the superior Fokker ''Zentralsteuerung'' system for all German aircraft, presumably including Albatroses.<ref name=Hegener3>Hegener 1961, p. 33.</ref><ref name=Volker6p34>Volker 1992, pt. 6, p. 34.</ref>

===== Electrical gears =====
Post First World War German fighters were fitted with electrical synchronizers.  In such a gear, a contact or set of contacts, either on the propeller shaft itself, or some other part of the drive train revolving at the same number of revolutions per minute, generates a series of electrical pulses, which are transmitted to a solenoid driven trigger motor at the gun.<ref name=Williams1.35/> Experiments with these were underway before the end of the war, and again the LVG company seems to have been involved: a British intelligence report from 25 June 1918 mentions an LVG two-seater fitted with such a gear that was brought down in the British lines.<ref name=Woodman7/> It is known that LVG built 40 C.IV two-seaters fitted with a Siemens electrical synchronizing system.

In addition, the Aviatik company received instructions to install 50 of their own electrical synchronization system on to DFW C.Vs (Av).