The Bristol Type 152 Beaufort was a torpedo bomber used by the Allies during World War 2.
Until the mid—1930s Britain had used only short range biplanes for torpedo-dropping. On August 27, 1935, the RAF issued a requirement for a long—range high-speed torpedo bomber. The Bristol Aeroplane Company responded to Design Specification M15/35 by offering its three—seat Type 150, a development of its recent submission for a new four-seat general reconnaissance aircraft, itself a stretched Type 142M Blenheim bomber (see Database, October 2005 Aeroplane).
On December 13 the Director of Technical Development disclosed Air Staff thoughts that a single design could combine the general reconnaissance (GR) and torpedo-bomber (TB) specifications, and on January 23, 1936, manufacturers were invited to submit proposals to Production Specification 10/36. Typical British logic decreed that the Blackburn Botha was the preferred design because Blackburn lacked work.
However, its marginally higher fuel consumption and 436 Imp gal fuel capacity offered significantly less range than the 570 gal of Brlstol’s proposed Type 152 (named Beaufort in December)‘ and it was accepted that a number of the latter would be needed for GR and torpedo squadrons based from Malta eastwards. One mandatory change was the addition of a fourth crew member, the price being a semi-exposed torpedo installation in both aircraft. Captain Frank Barnwell, Bristol's chief designer, was killed shortly before the Beaufort’s first flight and Leslie Frise subsequently developed the type.
Bristol's proposal to fit twin Browning 0-303in-calibre machine-guns in the gun turret was vetoed, as were twin Vickers drum-fed K guns. The special-to-type B.lV turret therefore had only one K gun, with 20 x 100-round ammunition drums. In May 1939, when the RAF wanted twin guns, the revised turret design was found unsuitable and the necessary modifications could not be incorporated until well into 1941.
The Air Ministry ordered 78 Bristol Perseus Vi-engined Beauforts off the drawing board on August 1, 1936. There were to be no pre-production prototypes, the first five machines instead serving as development air-craft. Then on November 2, Bristol proposed a change of engine in order to restore performance eroded by weight increases, suggesting its own new and undeveloped twin-row 1,000 h.p. sleeve-valve Taurus. This was accepted in July 1937, allowing planning and production to proceed.
During August 1938 the first Beaufort (L4441), stressed to 17,000lb. underwent ground-running trials that revealed the serious over-heating problems that would dog the Taurus throughout its life. Solutions were attempted and on October 15 Bristol‘s chief test pilot, Capt Cyril Uwins, taxied L4441 for 10min and then took off for a first flight. This still revealed overheating and was cut short to 15min by severe tail-plane vibration.
The next two short flights tested attempts to cure the tailplane and cooling problems and revealed that the latter were due to the inadequate airflow through the low-drag cowlings with their thrust-producing vertical cooling-air exit slots. Cooling was helped by fitting Blenheim-type cowlings with circumferential gills and by replacing the 7 1/2 in oil coolers with 10 1/2 in-diameter units, moved inboard by one rib space. Fuel jettison pipes for the outer tanks were also fitted.
Temporary tailplane bracing struts did not cure the vibration, but stiffer cockpit side windows did. A third problem involved handling difficulties when operating the undercarriage, owing to asymmetric drag caused by the aprons that closed the nacelles once the wheels were up. As the two oleos could not be made lo raise or lower simultaneously a severe yaw developed. The aprons were removed to improve handling, but the now-open nacelles created considerable drag. Despite this, L4441 achieved 304 m.p.n. at 15,000ft during trials at the Aeroplane and Armament Experimental Establishment (A&AEE) at Martlesham Heath lﬂ April and May 1939 with fully supercharged Taurus Ill engines producing 1,060 h.p. at 3,300 r.p.m. using 87-octane petrol. Side-hinged undercarriage doors were fitted later, and the fuel jettison pipes were moved outboard‘ to be in line with the oil coolers.
The second Beaufort, L4442, which featured smaller undercarriage aprons, flew on June 29, 1939, both early machines having rounded lower nose windows. These proved weak and created visual distortions, and from L4443 (which flew on July 26) optically flat windows were fitted. That machine also introduced standard side-hinged undercarriage doors.
The Assistant Chief of Air Staff recommended that the first six available Beauforts should go to No 22 Sqn for trials before any went over-seas, the plan being for 21 Beauforts to go to 100 Son and 50 to Australia. The outbreak of war on September 3 brought a change of plan; Beauforts were now needed for home-based TB and GR squadrons, early doubts about the Botha adding urgency. The first five aircraft had been virtually hand bullt, but on October 25, L4446. the first fully jigged mass-production aircraft, flew.
Speaking about a high-speed Blenheim replacement‘ the Chief of Air Staff stated on December 12 that a Beaufort with Hercules engines would have a top speed of 320 m,p.h.; but this and later plans for a faster Beaufort were stillborn.
The third prototype, L4443, was shipped to Karachi for tropical trials, which ran from February to May 1940 and involved cylinder and oil temperature checks with Taurus III and then Mk ll engines, Amazingly, there were no overheating problems and the tests were concluded on May 21. It then flew home. reaching Filton on the 29th. To improve handling L4443 featured a revised rudder trim tab with the chord increased by 4ln, increasing its area from 0.8ft2 to 1.25ft2 This change was incorporated on all Beauforts.
Poor directional control dogged all UK-built Beauforts except the turret-less trainers, so to overcome this the fin was slightly enlarged.
Production reached 30 aircraft a month during March 1940, a remarkable feat, but at the same time the A&AEE refused to clear the Beaufort for operational use because of "very bad single-engine flight characteristics". Urgent improvements, including improved inter-cylinder baffles to help cooling. brought clearance by mid-April.
The Beaufort design served as the basis for the Beaufighter.
- ↑ Warbird Resource Group
- ↑ Aeroplane Monthly. Kelsey Publishing Group. (Bristol Beaufort Database) May 2007 Page 59
- ↑ Aeroplane Monthly (Bristol Beaufort Database) May 2007 Pages 59 & 60
- ↑ Aeroplane Monthly (Bristol Beaufort Database) May 2007 Page 60
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