Bristol Beaufort


The Bristol Beaufort is a British twin-engined torpedo bomber designed by the Bristol Aeroplane Company, and developed from experience gained designing and building the earlier Blenheim light bomber. At least 1,180 Beauforts were built by Bristol and other British manufacturers.
Beauforts first saw service with Royal Air Force Coastal Command and then the Royal Navy Fleet Air Arm from 1940. They were used as torpedo bombers, conventional bombers and mine-layers until 1942, when they were removed from active service and were then used as trainer aircraft until being declared obsolete in 1945. Beauforts also saw considerable action in the Mediterranean; Beaufort squadrons based in Egypt and on Malta helped interdict Axis shipping supplying Rommel's Deutsches Afrikakorps in North Africa.
Although it was designed as a torpedo-bomber, the Beaufort was more often used as a medium day bomber. The Beaufort also flew more hours in training than on operational missions and more were lost through accidents and mechanical failures than were lost to enemy fire. The Beaufort was adapted as a long-range heavy fighter variant called the Beaufighter which proved to be very successful, and many Beaufort units eventually converted to the Beaufighter.
The Australian government's Department of Aircraft Production also manufactured variants of the Beaufort. These are often known collectively as the DAP Beaufort. More than 700 Australian-built Beauforts saw service with the Royal Australian Air Force in the South West Pacific theatre, where they were used until the end of the war.

Design and development

Origins

The Beaufort came from Bristol's submission to meet Air Ministry Specifications M.I5/35 and G.24/35 for a land-based, twin-engined torpedo-bomber and a general reconnaissance aircraft. With a production order following under Specification 10/36, the Bristol Type 152 was given the name Beaufort after the Duke of Beaufort, whose ancestral home was nearby in Gloucestershire. The competing torpedo bomber entry from Blackburn was also ordered as the Blackburn Botha; in an unprecedented step, both designs were ordered straight off the drawing board, an indication of how urgently the RAF needed a new torpedo bomber. 320 Beauforts were ordered. Initially, because of their commitment to the Blenheim, Bristol were to build 78 at their Filton factory, with the other 242 being built by Blackburn. These allocations would be changed later.
Although the design looked similar to the Blenheim, it was somewhat larger, with an 18 in increase in wingspan. The fuselage was longer in the nose and taller to accommodate a fourth crew member and the aircraft was considerably heavier. The larger bomb-bay was designed to house a semi-recessed torpedo or an increased bomb load. Due to the increased weight the Bristol Mercury engines on the Blenheim were to be replaced by more powerful, sleeve valve, Bristol Perseus motors. It was soon determined that even with the Perseus, the Beaufort would be slower than the Blenheim and so a switch was made to the larger Bristol Taurus engine, another sleeve valve design. For these engines, chief designer Roy Fedden developed special low-drag NACA cowlings, which exhausted air through vertical slots flanking the nacelles under the wings. Air flow was controlled by adjustable flaps.
The basic structure, although similar to the Blenheim, introduced refinements such as the use of high-strength light alloy forgings and extrusions in place of high-tensile steel plates and angles; as a result the structure was lighter than that of the Blenheim. The wing centre section was inserted into the centre fuselage and the nacelle structure was an integral part of the ribs, to which the main undercarriage was attached. Transport joints were used on the fuselage and wings: this allowed sub-contractors to manufacture the Beaufort in easily transportable sections and was to be important when Australian production got under way. The Vickers main undercarriage units were similar to but larger than those of the Blenheim and used hydraulic retraction, with a cartridge operated emergency lowering system.
The first prototype rolled out of Filton in mid-1938. Problems immediately arose with the Taurus engines continually overheating during ground testing. New, more conventional engine cowlings, with circumferential cooling gills, had to be designed and installed, delaying the first flight, which took place on 15 October 1938. As flight testing progressed, it was found that the large apron-type undercarriage doors, similar to those on the Blenheim, were causing the aircraft to yaw on landing. These doors were taken off for subsequent flights. On the second prototype and all production aircraft, more conventional split doors, which left a small part of the tyres exposed when retracted, were used.
The results of high level bombing tests carried out at Boscombe Down at an altitude of and an airspeed of showed that the Beaufort was, in the words of the test pilot, "an exceptionally poor bombing platform, being subject to an excessive and continuous roll, which made determination of drift particularly difficult". After 1941, British Beauforts were fitted with semi-circular plates on the trailing edges of the upper wing behind the engine nacelles to smooth airflow and improve directional stability.
As Blenheim production took priority and engine overheating problems continued, production was delayed; the bomber was first flown in October 1938 and should have been available almost immediately, it was not until November 1939 that production started in earnest. Several of the first production Beauforts were engaged in working-up trials and final service entry began in January 1940 with 22 Squadron of RAF Coastal Command.

British Beauforts

A total of 1,013 Taurus powered Mark Is were produced and a number of changes were introduced into the line. The original curved perspex bomb aimers' nose panels were replaced by flat, non-distorting panels from the 10th production aircraft. Successive Marks of the Bristol Taurus engine were installed: starting with the Taurus III, the more reliable Taurus IIs were used whenever possible. Initially Beauforts with the Taurus II engines were designated Beaufort Mk.II, while those with other Taurus Marks continued to be Beaufort Mk.Is. Finally all Taurus-engined Beauforts became Mk.Is with the introduction of the Pratt & Whitney Twin-Wasp-powered Beaufort Mk.II. The Taurus Mk.IIs were modified to Mk.IIa, which later became the Taurus Mk.VI. All of these versions produced. The final marks of Taurus engines used were the more powerful XII and XVIs. The Taurus engines drove de Havilland Type DH5/19 constant speed propellers.
As Beaufort units entered service, it was found that the defensive armament was inadequate and extra Vickers GO machine guns were fitted; two on a gimbal mounting in the forward nose and single guns on pivots on either beam. A remotely controlled Browning machine gun was fitted, firing to the rear under the nose. Housed in a clear blown transparency, it was found to be of little use and most operational units soon discarded them.
Fairey-Youngman pneumatic dive brakes were fitted to the wing trailing edges of several Beaufort IIs. After adverse reports from pilots these were locked shut. It was found that the curved alloy extensions on the trailing edges improved the flight characteristics and similar panels were fitted on all later production Beauforts.
When it became apparent that the Taurus engines had problems, planning commenced to re-engine the aircraft with Pratt & Whitney R-1830 Twin-Wasp radials, which were of similar diameter and slightly lighter, driving Hamilton Standard bracket-type variable-pitch propellers. There was no guaranteed supply of the Twin Wasp and production reverted to the Taurus-engined Mark Is after 165 Beaufort Mark IIs had been built, starting with AW244, which first flew in September 1941. Performance with the Twin-Wasps was marginally improved: maximum speed went up from and the service ceiling increased from. Normal range was reduced from.
Other modifications introduced on the Mk II used on late Mk Is included replacing the elongated direction finding antenna with a loop aerial enclosed in a clear, tear-drop fairing on the top of the cabin. ASV Mk III was added with yagi antennae under the nose and wings and a Bristol B1.Mk.V turret with two Browning machine guns was fitted. The final British-built version of the Beaufort was the Pratt & Whitney-powered T.Mk.II, with 250 produced from August 1943. In this version, the turret was removed and faired over. The last ever Beaufort was a T.Mk.II, which left the Bristol Banwell factory on 25 November 1944.

Australian-built Beauforts

As the design for the Beaufort began to mature, the Australian Government invited a British Air Mission to discuss the defence needs of Australia and Singapore. It was also a step towards expanding the Australian aircraft industry. The Beaufort was chosen as the best General Reconnaissance aircraft available and on 1 July 1939, orders were placed for 180 airframes and spares, with the specially formed Beaufort Division of the Commonwealth Department of Aircraft Production.
The Australian Beauforts were to be built at the established DAP plant in Fishermans Bend, Melbourne and a new factory at Mascot, New South Wales; to speed up the process drawings, jigs and tools and complete parts for six airframes were supplied by Bristol. The bulk of Australian-built Beauforts used locally available materials.
One of the decisive factors in choosing the Beaufort was the ability to produce it in sections. Because of this, railway workshops were key subcontractors:
Taurus engines, aircraft components and the associated equipment were shipped out to be joined in October 1939, by the eighth production Beaufort L4448. With the outbreak of war, the possibility that supplies of the Taurus engines could be disrupted or halted was considered, even before the British government placed an embargo on exporting war materials with the Blitzkrieg on France, the Netherlands and Belgium in May 1940. It was proposed that a change of powerplant could be made to the Pratt & Whitney Twin Wasp, which was already in use on Royal Australian Air Force Lockheed Hudsons. Orders for the engine were placed and a factory was set up at Lidcombe and run by General Motors Holden. The locally built engines were coded S3C4-G, while those imported from America were coded S1C3-4. Three-bladed Curtiss-Electric propellers were fitted to Beaufort Mks V, VI, VIII and IX while Beaufort Mks VA and VIII used Hamilton Standard propellers. In early 1941, L4448 was converted as a trials aircraft and the combination was considered a success. The first Australian-assembled Beaufort A9-1 flew on 5 May 1941 with the first Australian-built aircraft A9-7 coming off the production line in August. In total 700 Australian Beauforts were manufactured in six series.
A distinguishing feature of Australian Beauforts was a larger fin, which was used from the Mk VI on. Armament varied from British aircraft: British or American torpedoes were able to be carried and the final 140 Mk VIII were fitted with a locally manufactured Mk VE turret with.50 cal machine guns. A distinctive diamond-shaped DF aerial was fitted on the cabin roof, replacing the loop antenna. Other Australian improvements included fully enclosed landing gear and Browning M2 machine guns in the wings. Some were also fitted with ASV radar aerial arrays on either side of the rear fuselage.
The Mk.XI was a transport conversion, stripped of armament, operational equipment and armour and rebuilt with a redesigned centre fuselage. Maximum speed was and a payload of could be carried. Production of the Australian Beaufort ended in August 1944 when production switched to the Beaufighter.