Bristol Beaufighter
The Bristol Type 156 Beaufighter is a British multi-role aircraft developed during the Second World War by the Bristol Aeroplane Company. It was originally conceived as a heavy fighter variant of the Bristol Beaufort torpedo bomber. The Beaufighter proved to be an effective night fighter, which came into service with the Royal Air Force during the Battle of Britain, its large size allowing it to carry heavy armament and early aircraft interception radar without major performance penalties.
The Beaufighter was used in many roles; receiving the nicknames Rockbeau for its use as a rocket-armed ground attack aircraft and Torbeau as a torpedo bomber against Axis shipping, in which it replaced the Beaufort. In later operations, it served mainly as a maritime strike/ground attack aircraft, RAF Coastal Command having operated the largest number of Beaufighters amongst all other commands at one point. The Royal Australian Air Force also made extensive use of the type as an anti-shipping aircraft, such as during the Battle of the Bismarck Sea.
The Beaufighter saw extensive service during the war with the RAF, Fleet Air Arm, RAAF, Royal Canadian Air Force, United States Army Air Forces, Royal New Zealand Air Force, South African Air Force and Polskie Siły Powietrzne. Variants of the Beaufighter were manufactured in Australia by the Department of Aircraft Production ; such aircraft are sometimes referred to by the name DAP Beaufighter.
Development
Origins
The concept of the Beaufighter has its origins in 1938. During the Munich Crisis, the Bristol Aeroplane Company recognised that the Royal Air Force had an urgent need for a long-range fighter aircraft capable of carrying heavy payloads for maximum destruction. Evaluation of the Beaufort bomber concluded that it had great structural strength and stiffness in the wings, nacelles, undercarriage and tail, so that the aircraft could be readily developed further for the greater speed and manoeuvrability required by a fighter-class aircraft. The Bristol design team, led by Leslie Frise, commenced the development of a cannon-armed fighter derivative as a private venture. The prospective aircraft had to share the same jigs as the Beaufort so that production could easily be switched from one aircraft to the other.As a torpedo bomber and aerial reconnaissance aircraft, the Beaufort had a modest performance. To achieve the fighter-like performance desired for the Beaufighter, Bristol suggested that they equip the aircraft with a pair of its new Hercules engines, capable of around 1,500 hp, in place of the 1,000 hp Bristol Taurus engines on the Beaufort. The Hercules was a considerably larger and more powerful engine which required larger propellers; to obtain adequate ground clearance, the engines were mounted centrally on the wing, as opposed to the underslung position on the Beaufort. In October 1938, the project, which received the internal name Type 156, was outlined. In March 1939, the Type 156 was given the name 'Beaufighter'.
During early development, Bristol had formalised multiple configurations for the prospective aircraft, including variations such as a proposed Type 157 three-seat bomber outfitted with a dorsal gun turret with a pair of cannons, and what Bristol referred to as a "sports model", with a thinner fuselage, the Type 158. Bristol proceeded to suggest their concept for a fighter development of the Beaufort to the Air Ministry. The timing of the suggestion happened to coincide with delays in the development and production of the Westland Whirlwind cannon-armed twin-engine fighter. While there was some scepticism that the aircraft was too big for a fighter, the proposal was given a warm reception by the Air Staff.
The Air Ministry produced draft Specification F.11/37 in response to Bristol's suggestion for an "interim" aircraft, pending the proper introduction of the Whirlwind. On 16 November 1938, Bristol received formal authorisation to commence the detailed design phase of the project and to proceed with the construction of four prototypes. Amongst the design requirements, the aircraft had to be able to accommodate the Rolls-Royce Griffon engine as an alternative to the Hercules, and had to have maximum interchangeability between the two engines, which would feature removable installations.
Bristol began building an initial prototype by taking a partly-built Beaufort out of the production line, which sped progress; Bristol had promised series production in early 1940 on the basis of an order being placed in February 1939. Designers expected that maximum re-use of Beaufort components would speed the process, but the fuselage required more work than expected and had to be redesigned. Perhaps in anticipation of this, the Air Ministry had requested that Bristol investigate the prospects of a "slim fuselage" configuration. Since the "Beaufort cannon fighter" was a conversion of an existing design, development and production was expected to proceed more quickly than with a new one. Within six months the first F.11/37 prototype, R2052, had been completed. A total of 2,100 drawings were produced during the transition from Beaufort to the prototype Beaufighter; more than twice as many were made during later development, from the prototype to the production Beaufighter. Two weeks before the prototype's first flight, an initial production contract for 300 aircraft under Specification F.11/37 was issued by the Air Ministry, ordering the type "off the drawing board".
Prototypes and refinement
On 17 July 1939, R2052, the first, unarmed, prototype, conducted its maiden flight, a little more than eight months after development had formally started. The rapid pace of development was partly due to the re-use of many elements of the Beaufort design, and frequently identical components. R2052 was initially operated by Bristol for testing while it was based at Filton Aerodrome. Early modifications to R2052 included stiffening of the elevator control circuit, increased fin area and lengthening of the main oleo strut of the undercarriage to better accommodate weight increases and hard landings.During the pre-delivery trials, the first prototype R2052, powered by a pair of two-speed supercharged Hercules I-IS engines, had achieved 335 mph at 16,800 ft in a clean configuration. The second prototype, R2053, which was furnished with Hercules I-M engines and was laden with operational equipment, had attained a lower speed of 309 mph at 15,000 ft. According to aviation author Philip Moyes, the performance of the second prototype was considered disappointing, particularly as the Hercules III engines of the initial production aircraft would likely provide little improvement, especially in light of additional operational equipment being installed; it was recognised that demand for the Hercules engine to power other aircraft such as the Short Stirling bomber posed a potential risk to the production rate of the Beaufighter. This sparked considerable interest in the adoption of alternative engines for the type.
Roy Fedden, chief designer of the Bristol engine division, was a keen advocate for the improved Hercules VI for the Beaufighter but it was soon passed over in favour of the rival Griffon engine, as the Hercules VI required extensive development. Due to production of the Griffon being reserved for the Fairey Firefly, the Air Ministry instead opted for the Rolls-Royce Merlin to power the Beaufighter until the manufacturing rate of the Hercules could be raised by a new shadow factory in Accrington. The standard Merlin XX-powered aircraft was later called the Beaufighter Mk.IIF; the planned slim-fuselage aircraft, alternatively equipped with Hercules IV and Griffon engines, the Beaufighter Mk.III and Beaufighter Mk.IV respectively, were not built.
In February 1940, an order was placed for three Beaufighters, converted to use the alternative Merlin engine. The Merlin engine installations and nacelles were designed by Rolls-Royce as a complete "power egg"; the design and approach of the Beaufighter's Merlin installation was later incorporated into the design for the much larger four-engined Avro Lancaster bomber. Success with the Merlin-equipped aircraft was expected to lead to production aircraft in 1941. In June 1940, the first Merlin-powered aircraft conducted its first flight. In late 1940, the two Merlin-equipped prototypes were delivered. Flight tests found that the Merlins left the aircraft underpowered, with a pronounced tendency to swing to port, making take-offs and landings difficult and causing a high accident rate – out of 337 Merlin-powered aircraft, 102 were lost to accidents.
On 2 April 1940, R2052 was delivered to the RAF; it was followed by R2053 two weeks later. On 27 July 1940, the first five production Beaufighters were delivered to the RAF along with another five on 3 August 1940. These production aircraft incorporated aerodynamic improvements, reducing aerodynamic drag from the engine nacelles and tail wheel; the oil coolers were also relocated on the leading edge of the wing. The armament of the Beaufighter had also undergone substantial changes, the initial 60-round capacity spring-loaded drum magazine arrangement being awkward and inconvenient; alternative systems were investigated by Bristol.
Bristol's proposed recoil-operated ammunition feed system was rejected by officials, which led to a new system being devised and tested on the fourth prototype, R2055. The initial rejection was later reversed, upon the introduction of a new electrically driven feed derived from Châtellerault designs brought to Britain by Free French officers, which was quite similar to Bristol's original proposal. The initial 50 production aircraft were approved for completion with a cannon-only armament. The design of the cannons and the armament configuration was revised on most aircraft. The addition of six.303 Browning machine guns made the Beaufighter the most heavily armed fighter aircraft in the world, capable of delivering a theoretical weight of fire of up to per minute; the practical rate of fire was much lower due to gun overheating and ammunition capacity.
Further armament trials and experimental modifications were performed throughout the Beaufighter's operational life. By mid-1941, 20 Beaufighters were reserved for test purposes, including engine development, stability and manoeuvrability improvements and other purposes. In May 1941, the Beaufighter Mk.IIs R2274 and R2306 were modified to the Beaufighter Mk.III standard; removing the six wing guns and two inboard cannons to install a Boulton-Paul-built four-gun turret behind the pilot, to overcome the effect of recoil and nose-down tendency when firing the usual armament, was found to obstruct the emergency egress of the pilot. The fourth prototype, R2055, had its regular armament replaced by a pair of guns for attacking ground targets, a Vickers S gun mounted on the starboard fuselage and a Rolls-Royce BH gun mounted on the port fuselage; these trials also led to the Vickers gun being installed on an anti-tank Hawker Hurricane IID.