The second prototype at Martlesham Heath while undergoing acceptance trials. The Whirlwind was designed to meet Specification F.37/35, Britain’s first for a four-cannon fighter. Five of the eight manufacturers invited to tender responded, Boulton Paul and Hawker with single-engined designs and Bristol, Westland and Supermarine with twins.
The first two production Whirlwinds, P6966 (seen here) and P6967, were originally delivered to No 25 Sqn at North Weald in June 1940 for night-flying trials; but the unit was equipped with Bristol Beaufighters instead, and the two aircraft were reallocated to the first Whirlwind unit, No 263 Sqn, at Grangemouth.
Only two squadrons - Nos 253 and 137 - flew the Whirlwind operationally, the type’s last sortie being performed by the former on November 29, 1943, but not before the aircraft had proved itself a highly capable ground-attacker; bomb-equipped examples, as seen here, were dubbed “Whirlibombers”.
The Whirlwind’s ingeniously devised oil-cooler intakes were incorporated into the wing centre section, as seen here. Cooling air would enter via these "letterbox" intakes in the leading edge and be ducted through the spar to the three-element radiators buried within the centre section.
The second prototype Whirlwind, L6845, was tested with propellers of a one-off Rotol design, as seen fitted here. The first prototype, L6844, had been fitted with “handed” Peregrines driving de Havilland propellers, but the props of L6845 rotated in the same direction, the two aircraft sharing broadly similar handling characteristics.
A close-up of the experimental Roto I propeller blades fitted to L6845, but, significantly, not to production machines. Why L6845 was tested with these and not production D.H. props remains unclear. As a result the data acquired during trials was skewed.
Designated by Westland as the P.9, the prototype, L6844, sits outside the hangar at Boscombe Down before its first flight, in the hands of Westland’s chief test pilot, Harald Penrose, on October 11, 1938. Note the absence of the "bullet" fairing at the fin/tailplane junction later added to the aircraft, and all subsequent examples, to cure tail buffet.
Harald Penrose at the controls of Whirlwind P7110 in September 1941, by which time the aircraft had begun establishing a reputation as an exceptional weapon for lower-altitude duties, including ground-attack and intercepting low-level enemy intruders. This machine was written off during a forced landing near Warmwell, Dorset, in July 1943.
The standard de Havilland 54409 propeller blades fitted to production Whirlwinds are seen here on P6984 of No 263 Sqn. The D.H. props were considerably thicker than those used on L6845; a fact which significantly affected the type’s performance.