Interrupter Gear - Further Development

Further Development

In December 1915, the Vickers-Challenger interrupter gear was put into production for the Royal Flying Corps and in a few weeks a similar order for the Scarff-Dibovski gear was placed for the RNAS. Neither was a copy of the Fokker gear, as is sometimes reported - work on both was advanced before a captured Fokker was available for technical analysis. The first British aircraft to use these gears was the Sopwith 1½ Strutter which arrived in April 1916, although some other service types were retrofitted with synchronised guns about this time, including the Nieuport 12 and the Bristol Scout. Later British mechanical gears included the Ross, and Sopwith-Kauper gears. The main problem with all early mechanical synchronizers was that the rate of fire of the machine gun was dependent on the engine revolutions, and was slowed, especially when the engine was throttled back. The mechanical linkages were also very liable to failure, resulting in the unfortunate pilot shooting away his own propeller.

Eventually all British aircraft were equipped with the superior Constantinesco synchronization gear (or "CC" gear, invented by Romanian engineer George Constantinesco) which used sonic impulses transmitted by a column of liquid instead of a mechanical system of linkages. This was not only inherently more reliable, but delivered firing impulses at a much higher rate, so that a synchronised gun now fired at more or less the same rate as a normal machine gun, regardless of engine revolutions. The gear could also be easily fitted to any type of aircraft instead of having to have type-specific linkages designed. In addition, it was hard for the Germans to copy captured examples because it appeared to them to be a hydraulic system, whereas the actual principle of operation was based on Constantinescu's "theory of sonics", which remained secret until the end of the war. The Constantinesco gear remained in use with the Royal Air Force until the Second World War, the Gloster Gladiator being the last British fighter to be equipped with it.

A pilot would usually only have the target in his sights for a fleeting moment so a concentration of bullets was vital for achieving a kill. The obvious solution was to increase the number of guns. The final version of the Fokker Eindecker, the Fokker E.IV, came with two Spandau machine guns and this became the standard armament for all the German D-type scouts starting with the Albatros D.I. Fokker initially experimented with mounting three machine guns on the E.IV, but the extra weight rendered the aircraft virtually unflyable, and production E.IVs were fitted with two guns. The Allies did not field an aircraft with twin synchronized guns until the Sopwith Camel and the SPAD S.XIII came into service in mid-1917.