Armstrong Whitworth F . K . 8 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 . 2 c 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 unusual in having dual controls , enabling the observer to control the aircraft in the event of the pilot becoming incapacitated by enemy action . 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 still an unknown quantity , it was decided that 50 of the Armstrong Whitworth design , which was redesignated F . K . 8 . , would be ordered for the RFC . The production aircraft which followed 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 " had 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 vertical tailfin was modified . F . K . 8s had teething troubles , the oleo undercarriage was unable to withstand rough use on the frontline airfields , tailskids 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 Fighter s . 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 , gunner ' s seat and the exhaust system . The tall inverted vee radiators incorporated improved tubes which reduced the blockages . On later aircraft the nose cowling was redesigned . , and smaller box radiators were standardised . In service the F . K . 8 ( nicknamed the " Big Ack " ) proved to be effective and dependable , being used for reconnaissance , artillery spotting , ground - attack , contact - patrol and day and night bombing . It was reputedly easier to fly than the R . E . 8 , and was sturdier , but its performance was even more pedestrian , and it shared the inherent stability of the Royal Aircraft Factory types . While the pilot and observer were placed reasonably close together , communication between the two lacked the " tap on the shoulder " intimacy of the Bristol Fighter , or for that matter , the R . E . 8 . The F . K . 13 seems to have been the designation of a reconnaissance version of the F . K . 8 but it may have been a project . A total of 1 , 650 were built . Operational history . The F . K . 8 served with several squadrons on operations in France , Macedonia , Palestine and for home defence , proving more popular in service than its better known contemporary the R . E . 8 . The first squadron was 35 Squadron . The F . K . 8 was principally used for corps reconnaissance but was also used for light bombing , being capable of carrying up to six 40 lb ( 20 kg ) phosphorus smoke bombs , up to four 65 lb ( 29 kg ) bombs or two 112 lb ( 51 kg ) bombs on underwing rack s . Two Victoria Cross es were won by pilots of F . K . 8s ; one by Second Lieutenant Alan Arnett McLeod of No . 2 Squadron RFC , on 27 March 1918 and the second by Captain Ferdinand Maurice Felix West of No . 8 Squadron RAF on 10 August 1918 . With the R . E . 8 , the F . K . 8 was scheduled to be replaced for corps reconnaissance by a version of the Bristol Fighter with a Sunbeam Arab engine . Unfortunately the engine was unsatisfactory and this version of the Bristol never saw service . Like the R . E . 8 , the F . K . 8 was quickly discarded with the end of the war – the last squadron , No . 150 Squadron RAF , being disbanded at Kirec in Greece on 18 September 1919 . One F . K . 8 was purchased by a pilot named Sydney Stewart in the early 1920s . He took the aircraft to Buenos Aires and gave flying lessons . There he met Francisco Cusmanich , a Paraguayan pilot . Stewart and Cusmanich offered their services to the Paraguayan government during the Revolution of 1922 . The F . K . 8 was taken to Paraguay by ship . It received the name of " " Presidente Ayala " " in honor of the President of Paraguay at that time , Dr . Eusebio Ayala . Both pilots flew several reconnaissance and light bombing sorties over the rebel positions . In one of those sorties , the F . K . 8 was hit several times with ground fire causing an explosion on board , killing Stewart and Cusmanich instantly . Civil service . Eight aircraft were civil - registered after the war with two aircraft being used in Australia by the Queensland and Northern Territory Aerial Services ( later QANTAS , then Qantas Airways Ltd . ) . Western Front : Operators . Military operators . Home Defence : Macedonia : Palestine : Training :