The Boulton Paul Wulfruna

**Spinners** · August 16, 2015

Boulton Paul Wulfruna Mk.lb - No.1 Squadron, RAF Fighter Command, 1943

The 1939 Air Ministry specification F.18/39 (written around the Martin-Baker MB.3) called for a Hurricane and Spitfire replacement and stipulated a maximum speed of 400mph with a main armament of 6 x 20mm Hispano Mk.ll cannon. In early September 1939, at the outbreak of World War 2, Boulton Paul Aviation were approached by the Air Ministry and were asked to submit an insurance design to an essentially similar specification called F.18/40 but with an armament reduced to 4 x 20mm Hispano Mk.ll cannon. Boulton Paul's initial design submitted in January 1940 was a conservative-looking machine very much resembling a single-seat turretless Defiant and powered by the proposed Merlin 45 engine rated at 1,515hp although Boulton Paul soon realised that this was insufficient power for their design and also suspected that availability of any Merlin engine was always likely to be a problem. Boulton Paul bravely asked the Air Minsistry for permission to resubmit a new design to a later timescale utilising the promising new Bristol Centaurus 18-cylinder two-row radial that had been running on the bench since 1938 although development was deliberately slowed due to the demands for Hercules production. Permission was granted and the Boulton Paul designation of P.99 was given to the new design.

Forecasting that production Centaurus engines would not be available until the middle of 1942 Boulton Paul's Chief Designer, John Dudley North, played a slightly longer game and set out to create an advanced fighter aircraft that broke with the traditions of the time. Even though the overall diameter of the Bristol Centaurus was just 6% greater than the earlier Hercules engine, North wanted a low-drag installation quickly settling on a rear-mounted 'pusher' design with engine cooling provided by narrow, obliquely mounted intakes on the fuselage side. The remainder of the P.99 design was equally advanced being of all-metal construction with a canard configuration wing and a retractable tricycle undercarriage. The pilot was seated in an enclosed but roomy cockpit in the centre of the fuselage with good forwards visibility from the cockpit (although largely restricted to the rear by the large main wing, engine and fins) and ahead of the pilot was the powerful four cannon armament in a slightly staggered installation.

Despite the bombing of Boulton Paul's Wolverhampton works in early 1941, P.99 development moved smoothly through the Spring and Summer of 1941 although the advanced engine installation initially proved troublesome as it broke much new ground including the six-bladed propeller and extended drive shaft. Concurrently, Bristol Engines were working miracles in juggling Hercules production alongside development of the Centauraus and were able to ship prototype Centaurus IV engines to Boulton Paul during early 1942. This greatly assisted with design and installation and the Centaurus was especially neatly cowled with air outlets incorporating automatic sliding gills. By the Autumn of 1942 the first P.99 prototype was nearing completion and began ground-running trials during early December leading to the unfortunate discovery that the rear-mounted engine configuration caused cooling problems whilst on the ground - a problem that would follow the aircraft into operational service. Despite this, Boulton Paul were given a production order for 650 production P.99 aircraft and North's innovative design was officially bestowed with the unusual name of 'Wulfruna' as an historic nod towards Boulton Paul's Wolverhampton works.

Continued problems with the Centaurus delayed the first flight of the prototype Wulfruna until February 1943 but the initial test flights were successful except for minor vibration problems with the propeller and extended drive shaft and the aircraft was soon demonstrating level speeds of over 440mph and a very fast rate of climb although the range was slightly down on the official requirements and Boulton Paul's own estimates. Production commenced during the Spring of 1943 and the Wulfruna Mk.l entered service with No.56 Squadron in August 1943 and No.1 Squadron in September 1943 with the latter operating the Wulfruna Mk.1b in the night intruder role during the winter of 1943-1944.