The Armstrong Whitworth F.K.8 was a British two-seat general-purpose biplane built by Armstrong Whitworth during the First World War. The type served alongside the better known R.E.8 until the end of the war, at which point 694 F.K.8s remained on RAF charge. Design and development The aircraft, originally designated the F.K.7, was designed by Dutch aircraft designer Frederick Koolhoven as a replacement for the Royal Aircraft Factory B.E.2c and the Armstrong Whitworth F.K.3. It was a sturdier aircraft than the F.K.3, with a larger fuselage and wings, and was powered by a 160 hp (110 kW) Beardmore water-cooled engine. The undercarriage used oleo shock absorbers and the observer was equipped with a Scarff ring mounting for a .303 in (7.7 mm) Lewis machine gun. No armament was initially provided for the pilot. The rudder featured a long, pointed horn-balance. The type was fitted with basic dual controls for the observer to control the aircraft if the pilot became incapacitated. The first example, A411, flew in May 1916 and was delivered to the Royal Flying Corps Central Flying School at Upavon on 16 June. Because its rival, the Royal Aircraft Factory R.E.8 was an unknown quantity, it was decided that fifty of the Armstrong Whitworth design, renamed the F.K.8., would be ordered for the RFC. The production aircraft were identical in most respects to A411, with the addition of a forward-firing .303 in (7.7 mm) Vickers machine gun to port of and slightly behind the engine. The Armstrong Whitworth gun synchronising mechanism was incomplete at the time the first example A2636 arrived in France and some early production F.K.8s may have used the Arsiad interrupter gear instead. The Armstrong Whitworth mechanism (like other early mechanical synchronising systems) proved unreliable and was later replaced by the Constantinescu gear. From the fifth production aircraft, the rudder balance was shortened and the shape of the fin was modified. The type had several teething troubles: the oleo undercarriage was unable to withstand rough use on the front line airfields, tail skids frequently broke and the original radiators blocked up quickly. Following instructions issued on 30 April 1917, some F.K.8s were refitted with simplified vee-undercarriages from Bristol F.2 Fighters. This soon led to a temporary shortage of these undercarriages and the practice had to be discontinued until May 1918, after which several F.K.8s were fitted with revised undercarriages. Most production F.K.8s had modifications to the wings,