Foster mounting

It took several forms when applied to different aircraft types, but all shared the feature of a quadrant-shaped I-beam rail on which the gun could slide back and down in one movement.

Before the ready availability of a reliable synchronization gear, several methods were tried to mount a machine gun in a position from which it would be able to fire past rather than through the arc of the propeller.

The main difficulty, however, was the need for the pilot or gunner to have access to the breech of the gun, to change drums or belts as well as to clear jams.

[2] A hinged arrangement, permitting the breech to be swung back and down into a position where the pilot could change drums while in his seat was preferable, and several versions of such mountings enabled the Lewis (or Hotchkiss) guns of the French Nieuport 11 fighters to tackle the German Fokker Eindeckers in early 1916.

[4] The mounting also permitted the Lewis gun to be fired obliquely forwards and upwards, to attack an enemy aircraft from behind and below: a favourite tactic of several "ace" pilots, including Albert Ball.

Some pilots complained of quadrants twisting or breaking when subject to the forceful and clumsy handling inevitable in aerial combat, and some used elastic cord to replace or supplement the original clock-type spring fitted to assist returning the gun to its forward firing position.

In general, however, the mounting was highly successful: and for the RFC Nieuport squadrons at least much to be preferred to the unreliable early mechanical synchronisation gears.

[6] While Albert Ball continued to use the upward firing technique for some of his last victories, other pilots remarked on the great skill and marksmanship needed to achieve success with this manoeuvre in an S.E.5.

[13] The night fighter version of the Avro 504K was also armed with a "modified S.E 5a" type Foster mounted Lewis gun (see illustration at the head of this article).

This aircraft had a much larger gap between the top of the fuselage and the upper wing than most types fitted with this mounting and must have proved very awkward to use.