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The Blackburn Triplane was an anti-Zeppelin fighter designed to carry a Davis two-pounder quick-fire recoilless gun, but which only reached the prototype stage.
In 1915 Blackburn was given a contract to produce two examples of the A.D. Scout (or Sparrow), designed by Harris Booth of the Air Department of the Admiralty. This very unusual aircraft was designed to carry the Davis gun. It was a single bay pusher biplane, but with the small nacelle attached to the front of the upper wing. A large gap separated it from the lower wing, so the pilot was perched very high above the ground (at least for an aircraft of this small a size). The tail was equally unusual. It was connected to the main wings by braced struts. The horizontal surface was at the top, level with the upper wing. The fins and rudders were mounted below the horizontal surface. It had an early version of a tricycle undercarriage, with a pair of wheels mounted very close together under the front wing and tail skids carried wide apart at the base of the rudders. Four examples were built – two by Blackburn and two by Hewlett and Blondeau. They all went to RNAS Chingford, but were heavier than had been expected and proved to be unsurprisingly difficult to handle. They were all soon scrapped.
In 1916 Harris moved from the Air Department to Blackburn. One of his first projects was the Blackburn Triplane, a greatly modified version of his earlier A.D. Scout. It kept the same short nacelle, with the engine at the rear and the Davis gun carried under the pilot. In order to improve its rate of roll it was changed from a biplane to a triplane, so the wingspan could be reduced from 33ft 5in to 24ft while keeping the same wing area. Each wing carried a pair of ailerons, with the central ones controlled directly from the nacelle and the upper and lower ones by struts from the central aileron. The nacelle was carried in front of the middle wing. It had an enlarged version of the Scout’s tail, with longer fins and rudders to compensate for the greater height of the triplane wings. It did have a slightly more conventional undercarriage with a bungee-sprung V-type cross axle undercarriage in attached to the nacelle and skids on the rudders.
The aircraft was initially assembled in Roundhay Park, Leeds, for engine tests. It went to Eastchurch late in 1916 and made its maiden flight soon afterwards, powered by a 110hp Clerget engine powering a four bladed propeller. It was later tested with a 100hp Gnome engine powering a two bladed propeller. Remarkably it was actually accepted by the Admiralty on 20 February 1917, but like the A.D. Scout proved to be difficult to handle in the air. It was struck off on 19 March, after only one month in Admiralty hands. It was probably never actually given its gun.
Engine: Clerget or Gnome Monosoupape
Power: 110hp or 100hp
Crew: 1
Span: 24ft 0in
Length: 21ft 5 5/16in
Height: 8ft 6in
Empty weight: 1,011lb
All-up weight: 1,500lb
Armament: One Davis 2-pounder gun