The Boulton Paul P.92 was a design for a turret fighter armed with 20mm cannon, produced in response to a rather ambitious Air Ministry Specification.
The Air Ministry first called for a cannon armed turret fighter in Specification F.18/36, which called for a three man aircraft with a top speed of 375mph at 15,000ft and armed with four 20mm cannon in a turret. This triggered a period of discussions in which a wide variety of speeds and armament were considered, before the invitations to submit designs were issued in March 1937.
Specification F.11/37 of 26 May 1937 called for a three-man day and night fighter that was to be armed with four 20mm cannon carried in a turret with 360 degrees of traverse and -15 to +60 degrees elevation. The aircraft was to be able to carry 250lb of bombs and reach 370mph at 35,00ft. This specification attracted a great deal of attention, with Armstrong Whitworth, Short, Hawker, Bristol, Supermarine and Boulton Paul all submitting designs. A modified specification of early 1938, F.2/38, increased the performance demands, but was then cancelled.
This ambitious specification produced six designs, including J.D. North's P.92. This was a sleek high-winged two engined aircraft, with an unusual turret design. Instead of the normal 'dome' type of turret, which would have protruded way above the fuselage and caused massive drag, most of the turret on the P.92 was buried within the fuselage. At the top was a large shallow dome with a diameter of 13ft, several times the width of the fuselage, with the four 20mm cannon carried in a single horizontal row. The hope was that this would reduce drag and give the aircraft reasonable performance. This turret design was controversial within the turret, requiring a large turret ring that could very easily be distorted in flight, jamming the turret in place. The turret's central position in the middle of the wing meant that it would have been exposed to quite a bit of distortion, making a jam very likely.
The aircraft had shallow inverted gull wings, with the low point at the engine nacelles (this type of wing was often chosen on single engined aircraft to lower the main wheels and allow room for a large propeller, but that clearly wasn't the case here). It would have carried a crew of three - pilot, navigator and gunner.
In March 1938 Boulton Paul were given a contract to produce three prototypes of the P.92. One was to use two 1,760hp Rolls-Royce Vulture II engines, one to use Napier Sabre engines and one to test out the turret (also powered by the Vulture). Boulton Paul estimated that the Vulture powered prototype would be able to reach 371mph at 15,000ft and have a range of 2,000 miles. A mock up was completed by 31 May 1938. Work on the first two prototypes did get underway in the middle of 1939, but was at a very early stage when the entire project was cancelled on 26 May 1940. Boulton Paul were also heavily involved in the production of conventional bomber turrets, and this was felt to be more important than the speculative P.92.
One prototype was produced - the P.92/2. This was a half-sized version designed to test out the flight characteristics of the design and was built after wind tunnel tests with a 2/7th scale model suggested that the turret and cannon could cause excessive drag in some positions, which in turn forced the nose down.
It was built by Heston Aircraft in 1940, around a wooden monocoque and with a fixed undercarriage. This single test model was tested at Heston and Wolverhampton in 1941, and showed that the design flew successfully, without the problems suggested in the wind tunnel. The test aircraft was later Boscombe Down in 1943, well after the end of the main project, where once again it performed acceptably, although the drag levels were higher than expected.
Alternative uses were suggested for the low profile turret, including the idea of fitting it as dorsal and ventral turrets on the Avro Manchester, and its use on a modified version of the Handley Page Halifax, the H.P.58. Handley Page was awarded a contract to produce a prototype of the H.P.58, and a mock up of the turret installation was produced. Problems with the working turret meant that the H.P.58 project was cancelled.
P.92 (performance figures estimates)
Engine: Two Rolls-Royce Vulture IIs
Power: 1,710hp each
Span: 66ft 3in
Height: 15ft 3in
Loaded weight: 19,100lb
Maximum take-off weight:
Max speed: 299mph at sea level; 371mph at 15,000ft; 352mph at 30,000ft
Climb Rate: 3,200ft/min to 15,000ft
Service ceiling: 38,000ft
Endurance: 1.5 hr
Armament: Four 20mm cannon in power operated turret
Engine: Two de Havilland Gipsy Major II inline engines
Power: 130hp each
Maximum take-off weight: 2,778lb
Max speed: 152mph
Cruising speed: 135mph