The Boulton & Paul P.33 Partridge was a single seat biplane fighter designed to the same specification as the Bristol Bulldog.
Air Ministry Specification F.9/26 called for a fighter to replace the Armstrong Whitworth Siskin and the Gloster Gamecock, then in use with thirteen fighter squadrons. This would be a lucrative order, and eventually nine prototypes of different designs would be ordered.
The P.33 Partridge was a conventional single biplane fighter. It used Boulton & Paul's Locked Joint System, based on the use of steel tubes made from rolled steel strips (to improve the quality of the tubes) and used many of the same components as the P.29 Sidestrand bomber, the first Boulton & Paul designed military aircraft to enter production.
The P.33 had Boulton & Paul's standard square tipped wings, with dihedral on the lower wing and a level upper wing. Each wing was made from two parts, with two halves of the upper wing joining above the fuselage. The aircraft was built with Frise ailerons on the upper wings, but they were added to the lower wing before the aircraft was delivered for official evaluation. The upper and lower ailerons were connected by rods. The upper wing was larger, with a span of 35ft and chord of 5ft 6in, compared to 31ft and 4ft 6in on the lower wing.
The engine was contained within a streamlined nose, although the heads of the cylinders were exposed outside the cowling. The fuselage had an oval cross section. The pilot was located just behind the wing, with a cut out in the upper wing to improve visibility.
The original design, produced before the full details of the specification had been issued, used the Bristol Jupiter engine. When the details came out, John North, Boulton & Paul's chief designer, changed to the more powerful Bristol Mercury, but that engine was still under development. The prototype was completed with a 440hp supercharged geared Jupiter VII engine. This engine would have been used in early production aircraft (the Mk II), while the Mercury would have been used in the Mk III (the Mk I was the prototype).
The design ran into problems with the location of the guns. Boulton & Paul's original design was judged to have the guns mounted too low. A modified design was felt to have them mounted too high for the pilot to easy clear jams, and in order to match the Ministry's preferred location the guns had to be mounted on the sides of the fuselage, in bulges that increased drag.
A single prototype was built (J8459), and made its maiden flight early in 1928. It was then displayed in the New Types Park at Hendon.
A large number of designs were submitted to this specification, and nine prototypes were ordered from various manufacturers (including the Armstrong Whitworth Starling, Avro Avenger, Blackburn Turcock, Bristol Bulldog, Hawker Hawfinch, Vickers 141 and Westland Wizard). The Hawker Hawfinch and Bristol Bulldog were both judged to be superior to the Partridge and the eventual order went to the excellent Bristol Bulldog.
A number of flaws were reported with the Partridge. The undercarriage was considered to be too spongy and too narrow. The aircraft was longitudinally unstable and difficult to control. It was difficult to pull the aircraft out of a dive, and it wasn't a good aerobatic aircraft. Despite these flaws it was unofficially placed third behind the Hawfinch and the Bulldog. A modified version of the design, the Boulton & Paul P.34, was put forward for N.21/26, a specification for a naval fighter, but didn't reach the prototype stage.
Engine: Bristol Jupiter VII
Span: 35ft (upper), 31ft (lower)
Length: 23ft 1in
Empty weight: 2,021lb
Loaded weight: 3,097lb
Maximum take-off weight:
Max speed: 167mph at 10,000ft; 164mph at 20,000ft, 152.5mph at 26,000ft
Climb Rate: 6min 30sec to 10,000ft; 15min 4 sec to 20,000ft, 26min 19sec to 26,000ft
Service ceiling: 28,950ft
Armament: Two fixed forward firing Vickers machine guns
Bomb load: Four 20lb bombs