O.Tapper Armstrong Whitworth Aircraft since 1913 (Putnam)

The Koolhoven Multiplanes

   In the early stages of the 1914--18 war, before the pattern of aerial warfare had developed, there was a school of thought in Great Britain which argued the merits of the 'flying battleship' or 'aerial destroyer'. This concept, which envisaged a large aeroplane with a multiplicity of guns having a wide field of fire, arose perhaps from the nation's deep-seated naval traditions. The proponents of the theory gave little regard to the virtues of speed or manoeuvrability, the idea apparently being that the aircraft would proceed in a dignified fashion, possibly in line ahead, firing broadsides at the enemy, who, it might be supposed, would adopt similar tactics. This may be extending the analogy too far, but the fact remains that considerable effort was expended in devising large fighter aeroplanes in which performance took second place to armament. Needless to say, the concept proved unsound, and it was the more adaptable fixed-gun fighter which dominated the scene where the battles were actually fought.
   The large multi-seat-fighter notion certainly produced some odd-looking aircraft, with both Sopwith and Vickers trying their hand at the idea, but perhaps the strangest of all were the two Armstrong Whitworth triplanes produced to the designs of Frederick Koolhoven. The first of these featured two machine-gun nacelles mounted on the top surface of the middle wing, which was considerably longer than the other two. In order to provide the best possible field of fire for the two gunners, the nacelles projected well forward of the tractor propeller, which was situated but a few inches ahead of the wing leading edge. The pilot was placed behind the wings where his view in any direction, except upwards and backwards, must have been minimal. The engine was the new 250 hp Rolls-Royce twelve-cylinder unit which later became known as the Eagle. The undercarriage, which, like the rest of the aircraft, was highly unconventional, consisted of a single centrally placed shock-absorber strut terminating in two closely-spaced wheels, lateral stability being provided by a small single wheel under each wingtip. The tail was supported by a skid carried on long struts emanating from the underside of the fuselage at a point just aft of the wings. The whole aircraft seemed ill-balanced and gave the impression of frailty, and it is, perhaps, not surprising that Fairbairn-Crawford, the works manager, is on record as saying that he refused permission for it to be flown.

P.Lewis The British Fighter since 1912 (Putnam)

The F.K.11 was not proceeded with but another design from Armstrong Whitworth, the three-seat F.K.5, also exhibited some equally remarkable features. It was built as the result of a War Office requirement for a multi-seat, long-range escort and anti-Zeppelin fighter, a specification to which Vickers and Sopwith also constructed prototypes.
   Armstrong Whitworth proceeded to build the F.K.5 as a large triplane with its central planes of much greater span than those above and below. The 250 h.p. Rolls-Royce engine turned its propeller immediately in front of the leading edge and between the pair of gunners’ nacelles fitted to the centre wings. A revised version as the F.K.6 was built with a different fuselage, undercarriage and nacelles but, as with so many extremely unconventional designs, the machine was not a success.