Bristol Boxkite

The Boxkite (officially the Bristol Biplane) was the first aircraft produced by the British and Colonial Aeroplane Company (later known as the Bristol Aeroplane Company). A pusher biplane based on the successful Farman III, it was one of the first aircraft types to be built in quantity. As the type was used by Bristol for instruction purposes at their flying schools at Larkhill and Brooklands many early British aviators learned to fly in a Boxkite. Four were purchased in 1911 by the War Office and examples were sold to Russia and Australia. It continued to be used for training purposes until after the outbreak of the First World War.

The original intention of Sir George White, the founder and chairman of Bristol Aircraft, was to build licensed copies of the Zodiac biplane, designed by Gabriel Voisin. One example of this design was imported from France and exhibited by Bristol at the 1910 Aero show in London in March 1910, and afterwards taken to Brooklands for flight testing. Initial attempts to get it to fly were entirely unsuccessful. This was largely due to its unsatisfactory wing section (the shallow camber of the Zodiac's wings had been commented upon by the aviation journal Flight), but the aircraft was also underpowered for its weight, and a new set of wings did little to improve performance. A single brief flight on 28 May was achieved by Maurice Edmond, but after an accident that damaged its undercarriage on 10 June it was abandoned, as was work on five more examples being built at Bristol's factory at Filton.

Sir George was advised to acquire rights to build copies of the successful Farman biplane. This proved impossible since George Holt Thomas was negotiating rights with the Farman company, but George Challenger, the chief engineer at Filton, believed that he could produce a satisfactory copy since full details of the Farman machine had been published in Flight. This was authorized by Sir George, and Challenger set to work on drawings for a new aircraft. The first example was constructed in a matter of weeks, using some components from the abandoned production Zodiacs, and was delivered to the company's flying school at Larkhill on Salisbury Plain, where it was first flown on 30 July 1910, piloted by Maurice Edmond. Farman sued Bristol for patent infringement, but the company's lawyers claimed substantial design improvements in matters of constructional detail, and the lawsuit was dropped.

The Boxkite was a two-bay biplane with an elevator carried on booms in front of the wings and an empennage consisting of a pair of fixed horizontal stabilisers, the upper bearing an elevator, and a pair of rudders carried on booms behind the wing. There were no fixed vertical surfaces. Lateral control was effected by ailerons on both upper and lower wings. These were single-acting, the control cables arranged to pull them down only, relying on the airflow to return them to the neutral position. The wings and fixed rear horizontal surfaces were covered by a single layer of fabric: the other surfaces were covered on both sides.

Power was usually provided by a 50 hp (37 kW) Gnome rotary engine, although other engines were also used. The engine was mounted on a pair of substantial wooden beams mounted above the lower wing: these continued forward to carry the seats, which were arranged in tandem, with the pilot sitting over the leading edge of the wing. The undercarriage consisted of a pair of long skids, each bearing a pair of wheels sprung by bungee cords, and a single sprung tailskid mounted below the leading edge of the lower tailplane.

The first two Boxkites, assigned works numbers 7 and 8, differed in detail from the later production aircraft; the front outrigger booms were braced by a pair of vertical struts and were attached to the ends of the interplane struts. This arrangement was inherited from the Zodiac, being necessary in that aircraft because the front spar of the wing did not also form the leading edge. Additionally the rear elevator had a straight trailing edge. No. 8 also had double-surfaced wings; the wings of No. 7 were single-surfaced with the ribs enclosed in pockets, like production aircraft. No. 7 was initially fitted with a 50 hp (37 kW) Grégoire, but for its first flight this was replaced by a Gnome, although the Grégoire was later refitted for trial purposes: No. 8 had a 50 hp (37 kW) E.N.V.

The first examples built had upper and lower wings of equal span, although most of the aircraft eventually produced had an extended upper wing and were known as the Military Version. The examples of this type sold to the Russian government and the first aircraft sold to the British Army were fitted with a third rudder hinged to the centre leading-edge interplane strut of the tailplane, but this was not made standard.

Two modified Boxkites were produced for competition purposes. The first, No. 44, was a single-seater built to compete in the 1911 Circuit of Europe air race and had reduced wingspan and a nacelle for the pilot, similar to the Bristol Type T. The second, No.69, was a redesign by Gabriel Voisin, who was employed as a consultant by Bristol. This had no front elevator, monoplane tail with a single rudder, and a reduced gap between the wings. It was tested at Larkhill in February 1912, but was evidently unsuccessful since it was soon rebuilt as a standard Boxkite and was to crash in November 1912.