Bristol B.152 Beaufort
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 570gal of Bristol'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.IV 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 aircraft. 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.
Except for wooden doors and fabric-covered control surfaces the Beaufort was of stressed-skin light alloy construction. The semi-monocoque fuselage, built in three sections, was shaped by lipped channel and Z section formers, multiple at the fuselage and other joints and other points of major stress, connected by angles-ection stringers.
Most construction was of Alciad or aluminium, but Hidaminium sections were used at the fuselage/fuselage and fuselage/wing joints. The front fuselage extended forward from the wing front spar and housed the pilot and navigator/bomb-aimer. Armour was fitted ahead of the instrument panel, but the V~windscreen, which incorporated clear vision panels and a ring-and-bead sight for the fixed gun(s), was unprotected. When fitted, the torpedo sight was above the pilot's head.
The rear fuselage, strengthened near the turret and incorporating three heavy longerons, extended aft from the front spar to the stern frame and housed the Wireless Operator/Air Gunner (WOp/AG) and rear gunner. Aft of the radio compartment between wing spars was an armour plate partition and then the 27in-wide two-part main entrance hatch. Inside this was a chemical toilet, which doubled as a step. The long cabin was 54in wide. The fuselage was cut away in an inverted 'V' aft of the turret to improve the turret gunner's field of fire. The stern frame carried the hori zontal and vertical tail surfaces and self-centring tailwheel. The latter retracted into a waterproof well, but was often locked down.
Bristol's original design for the 100in-long bomb bay could not accommodate four Small Bomb Containers side-by-side with the bomb doors fully closed and so the lower fuselage was widened to 60in, giving it its characteristic bell-shaped cross section. Primarily designed to accommodate four 2501b anti-submarine bombs side-by-side, or two of the bulkier 2501b "B" or 5001b general purpose (GP) bombs, it was found on operations that combinations of two 2501b plus two 5001b GP/medium capacity (MC) bombs, tour slim 5001b semi-armour-piercing (SAP) bombs or four 2501b depth charges would fit. Fore-and-aft extensions formed the 19ft torpedo cell. A special rack could be fitted in lieu of bomb carriers to accommodate a torpedo, a magnetic mine or a 2,0001b bomb.
The RAF 28 aerofoil section cantilever wing was built in three main sections, with the outer panels bolted to the outer ends of the centre-section spars. The whole structure was based on two spanwise spars with full-depth webs and op and bottom extruded booms. The centre section was continuous through the fuselage, bearing all weights and forming the roof of the bomb bay. Square-section steeltube mounts on tubular bearers were fitted near the outer ends of its parallel spars for the engines and main undercarriage, which were housed in streamlined nacelles. Inboard of these between the spars were the two main 194 Imp gal fuel tanks.
A four-man inflatable dinghy was stored in the port wing root. The spars of the otherwise similar outer wing panels tapered and converged towards the detachable wingtips. Each housed an oil cooler and a 91 Imp gal fuel tank with a fuel jettison pipe, just outboard of which were pick-up points for an external 2501b bomb carrier. The leading edge of the port outer wing housed twin adjustable landing lights and inboard of these was a fixed 0.303in-calibre Browning gun with 300 rounds, The ailerons comprised alclad ribs on a tubular duralumin spar, and hydraulically-operated split flaps were fitted between these and the fuselage. Similar construction was used for the tail surfaces, and the elevators and rudder were similar to the ailerons.
The underslung engines driving 12ft-diameter de Havilland/Hamilton two-position propellers were in long cowlings with the exhaust collector rings forming the nosings. The undercarriage members retracted backwards hydraulically into the engine nacelles, the doors being closed by elastic cords.
During August 1938 the first Beaufort (L4441), stressed to 17,0001b, underwent ground-running trials that revealed the serious overheating 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 tailplane 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 7.5in oil coolers with 10.5in-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 to 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.h. at 15,000ft during trials at the Aeroplane and Armament Experimental Establishment (A&AEE) at Martlesham Heath in April and May 1939 with fully supercharged Taurus III 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.
The outbreak of war on September brought a change of plan; Beaufor were now needed for home-based TB and GR squadrons. The first five aircraft had been virtually handbuilt, but on October 25, L4446, the first fully jigged mass production aircraft, flew.
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 II engines. There were no overheating problem 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 4in, increasing its area from 0.8 sq.ft to 1.25 sq.ft. This change was incorporated on all Beauforts.
Poor directional control dogged al 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, 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 intercylinder baffles to help cooling, brought clearance by mid-April.
The presence of beam approach equipment was indicated by a long dipole aerial under the rear fuselage. On early aircraft the upper aerial for this equipment was housed within the radio mast, but later took the form of a blade aerial ahead of the turret. Semicircular trailing edge extensions were fitted behind the engine nacelles in mid-1941 to cure turbulence over the wing, This useful modification added 10 m.p.h. to the top speed but was not needed on the Mk II series, as the larger diameter Twin Wasp engines eliminated the turbulence. From W6537 onwards (the 410th UK-built machine) a Browning gun was installed in the starboard wing (500 rounds) and maximum permitted take-off weight raised from 20,000 to 21,0001b, by when the armoured bulkhead had been replaced by armoured seat backs for the pilot and WOp/AG. From the summer of 1941, 22 Sqn began to fit a Vickers K gun firing forward in the upper nose.
When all Beauforts were grounded during the late summer of 1940 in order to replace the troublesome Taurus III engines with a modified version of the moderately supercharged Taurus II using 100-octane fuel and now producing 1,130 h.p., the opportunity was taken to make all five fuel tanks self-sealing and to fit armour to the rear spar to protect the four fixed tanks. Frequent schemes for more armour, which offered some protection from fighters but little against flak, had always to be set against the need for new operational equipment, both exacerbating the type's weight problems.
All Taurus engines featured singlestage superchargers and from then onwards used 100-octane fuel. The Taurus II had a low-speed impel which was cropped and ran at higher gear speed on the Mk VI. These two marks became the XII and XVI when the crankshafts, maneton joints, bearings and other features were modified for added reliability. Air Publication 3208 credits these four versions with a maximum output of 1130 hp at 3,100 r.p.m. There was a lack of uniformity between individual machines, especially before mid-1942.
Problems with the early Taurus engines, and Bristol's desire to concentrate on the larger Hercules, led to the American Pratt & Whitney (P&W) Twin Wasp S3C4-G being adopted as an alternative. This was a two-stage engine producing 1,200 h.p. at 2,700 r.p.m., with the exhaust collected at the rear of the engine and emerging aft of the cooling gills. Propellers were 11 ft 6in fully feathering Curtiss Electrics. Beaufort Mk 1 N1110 was converted and flew as a prototype in November 1940. The 485 Mk Is were followed by ten interim Mk 11 aircraft; virtually Mk Is with Twin Wasp engines. Next came 45 production Mk IIs, which featured air-to -surface -vessel (ASV) radar. A small circular loop mounted in a streamlined housing replaced the large folding direction-finding (DF) loop. This was fitted to all future British TBs, although omitted from those later laid down as trainers. Jettison pipes for the inner fuel tanks were fitted at the rear of the engine nacelles.
The bombing of Daimler's production line for the B. IV gun turret led to the adoption of the Bristol B.1 turret for future Beauforts. This was the Mk V, a well-armoured but nonretractable version of the Blenheim turret and carried twin Brownings with 950 rounds per gun. The next 110 Beauforts featured this, strengthened engine and undercarriage bearers and a thicker wing skin. The permitted underwing bomb load was doubled. With these modifications the aircraft became the M1k IIA. Heavy shipping losses in the Atlantic so reduced supplies of Twin Wasps that Taurus engines were installed in the next 529 machines, which were otherwise identical to the Mk IIA and designated Mk IA. These introduced twin nose guns which were fitted retrospectively to earlier machines. Once supplies of Twin Wasps permitted, the Mk IIA was reintroduced and 129 more torpedo bombers were built. With requirements met, a final batch of 121 machines was laid down as unarmed dual-control advanced trainers. A few torpedo-bombers were also converted to trainer standard.
In the UK all Taurus engines and major airframe components were manufactured at Bristol's works. Bristol B.IV gun turrets were manufactured by the Daimler Car Company and Bristol B.1 turrets by the Brockhouse Company. Most Beauforts were assembled at Filton and flown out from there. However, to provide space for the new Buckingham, the final 250 were assembled at Bristol's shadow factory at Banwell from stockpiled parts and flown out from Oldmixon after completion. Twin Wasp engines for the 415 Mk ll-series aircraft were all imported from the USA.
A planned twin-float Beaufort for Australia and Canada was not built; neither were the projected Mk III with Rolls-Royce Merlin engines, nor the Mk IV with improved Taurus XX engines, in both cases because the engines were not available. The M1k III was originally to have had the Merlin XX, but it was quickly appreciated that the Mk 30 was more suitable. However, Rolls-Royce had not developed a twin installation version and the whole scheme lapsed. The Taurus XX engine, with two-speed blowers and fully-feathering propellers, was flight tested in AW372, which featured an Australian-style enlarged fin. This was not a true prototype Mk IV, however, as it lacked the intended B.15 four-gun turret, eventually flight tested in EK997. It was intended that the final 500 Beauforts would be Mk IVs, but Bristol lacked the Coastal command’s first Beaufort, L4447, joined 22 Sqn at Thorney Island on November 15,1939. After delays caused by engine problems operations began on April 15, 1940, laying magnetic mines in the German Bight. Bombing attacks against land and sea targets commenced in May with the first British 2,0001b armour piercing (AP) bombs being dropped on the 7th against minor vessels.
Even before the war had started, it had been agreed that Australia's Department of Aircraft Production (DAP) would supply the Royal Australian Air Force and overseas-based RAF units with Beauforts.
In August 1938 the as-yet unflown Beaufort was identified as the best available design to meet Australia's coastal defence needs, and in the following March it was agreed that Australia would build Beauforts for the RAAF and for overseas-based RAF units.
To assist local production two complete airframes and 20 complete sets of airframe parts were promised by Bristol, who trained 78 key Australian personnel and sent 20 of their staff to Australia. Bristol's customary tardiness caused delays, but on October 20, 1939, Beaufort L4448, which had been built without engines, at last le ft Filton for Australia. Component production for the Australian Beaufort would be spread among plants in south eastern Australia, with final assembly at Fishermen's Bend in Victoria and Mascot, New South Wales, all under the control of the Beaufort Division of the Department of Aircraft Production (DAP).
In April 1940, by which time it had been decided that all Australian Beautorts would have Twin Wasp engines, reassembly of L4448 was under way, with the Commonwealth Aircraft Corporation responsible for fitting its engines. However, Britain's desperate war situation forced an embargo on the export of strategic materials and progress on completing the Beaufort and converting it to take the new engines was slow: the promised second machine, L9811, was not supplied.
By this time the RAAF and RAF had each ordered 90 aircraft. The RAAF order was increased in early 1941 as more Hudsons were unavailable. Although the UK's export embargo was lifted by the end of 1940, the bombing of Bristol's works continued to hinder all forms of assistance to Australia, as did the sinking of ships carrying supplies from the UK and USA. Until local production was in full swing Australia had to import such key items as engines and propellers.
On May 5, 1941, L4448 made its first flight, and T9540, the first Australian Beaufort built from imported parts and the first of the RAF order, flew on August 22 from Fishermen's Bend, achieving a speed of 271 m.p.h. on test.
Production at Mascot was delayed and its first machine, T9545, did not fly until October 20, the month when first deliveries to 100 Sen, the RAF's Australian detachment, began, Most were built as GR Bombers but a number were completed to GR Torpedo standard, all designated Mk 11. Following the transfer of 100 Sqn and its 17 aircraft (two having been lost) to the RAAF, Britain allocated its order for 90 Beauforts to Australia. A change to RAAF A9 series serial numbers began before this order had been completed.
Basic design and construction followed UK practice, the most significant change being the enlargement of the fin from 11 .4 sq.ft to 14.3 sq.ft to improve stability, The mainwheels were fully enclosed by additional doors at the rear of the engine nacelles, The use of ball bearings was reduced by some 50 per cent.
Before February 1942 most Beauforts, including those sent to Singapore, were unnecessarily fitted with the semi-circular trailing edge extensions typical of Taurus-engined machines, The fitting and later deletion of chin guns, the fitting of nose guns and the change of gun turret followed British practice, but the DAP also fitted a forward-firing Vickers K gun in a glazed section of the cabin roof above the beam guns.
After completion of the first 50 aircraft a temporary shortage of P&W S3C4-Gs led to S1C3-G single-stage engines being fitted to the next 100, degrading their altitude performance, A subsequent shortage of Curtiss Electric propellers led to the second 90 aircraft being fitted with de Havilland/Hamilton units, as fitted to Taurus-engined machines.
In RAAF service the first batch became the Mk V; the next 40, with non-standard engines and Australian ASV radar, became the Mk V1; the next 60, with both non-standard engines and propellers, the Mk VII and the next 30, with non-standard propellers, the Mk VA (Mk VIII having already been allocated to a new definitive version similar to the British Mk IIA). The 520 Mk VIIIs introduced twin nose-guns, fitted retrospectively to earlier marks, and many Mk VIIIs from the A9-54X-range onwards received 0.5in-calibre wing guns.
Major crisis was caused during 1943 by the failure of locally produced Breeze actuators for elevator trim tabs. These had been manufactured from unsuitable materials and were found to have been the cause of a large number of fatal crashes.
Although early supplies of Twin Wasps were imported from the USA, General Motors (Holdens) manufactured 870. Final assembly was at Fishermen's Bend (A9-odds) and Mascot (A9-evens, although 451 was built there). Peak output reached 37 in September 1943.
During 1944 some 46 airframes, mainly Mk VIIIs, were reconstructed as Mk IX transport aircraft, with their turrets and military fittings removed, with the exception of bomb shackles, and the fuselage top line raised aft to provide space for five airliner-type seats. Virtually new, these were given new serial numbers. The last, A9-746, was delivered in October 1945. All marks of Beaufort remained Bristol Type 152.
The transfer of the RAF's No 100 Sqn to the RAAF was announced on February 28, 1942 (made retrospective to the 25th). The transfer was seamless and the RAF pattern of shipping escort and anti-raider patrols continued. The first offensive mission was flown on May 27, when two Beauforts staged through Port Moresby, New Guinea, to reconnoitre the Deboyne Islands.
Four weeks later two Beauforts of another detachment bombed shore targets at Salamaua on New Guinea while five others bombed a ship reported as under way off Lae in north-eastern New Guinea, but what was in fact the wreck of the Tenyo Maru, which had been beached after bombing by US Navy aircraft on March 10.
In the shape of No 489 Sqn, an Article XV unit within RAF Coastal Command, the Royal New Zealand Air Force received six Beaufort Mk Is between August and October 1941. However, various crises overseas led to these being withdrawn by the following April before the unit could become operational.
The early story of No 415 Slain Article XV unit of the Royal Canadian an Air Force (RCAF), was similar to that of 489 Sqn. At Sidney, Vancouver Island, the metropolitan RCAF took over the Beauforts of the RAF's 32 OTU to form the emergency 32 Sqn RCAF, and used them on torpedo and bomb-armed anti-shipping searches over the eastern Pacific at the time of the Japanese attack on Pearl Harbor in December 1941. This was repeated during May and June 1942 when the Aleutian Islands were attacked and Canada threatened. The RCAF formed its own 149 (TB) Sqn with the 12 surviving Beauforts at the same base in November 1942, retaining them until August 1943 without becoming operational.
From January 1942, 18 Beaufort Mk Is joined the South African Air Force (SAAF), equipping 36, 37 and HO Flights in the Union, Patrols over the southern oceans were flown before the numbered Flights took part in the capture of the Diego Suarez area of Madagascar in May. Before the subsequent occupation of the whole island the two Flights were amalgamated, together with No 32 Sqn's Martin Marylands, to form 20 Sqn in July. This unit was in turn renumbered No 16 Sqn SAAF in September. The Beauforts fared badly because there were no spares on the island and the SAAF was still imposing the outmoded maximum take-off weight of only 18,500 lb.
Before the ten surviving Beauforts were returned to the RAF a few had served with other units in the Union. Meanwhile 16 Sqn had converted to Blenheim Vs and moved to North Africa as an A/S patrol unit. During June 1943 the Blenheims made way for a mixed complement of Taurus and Twin Wasp-engined Beauforts. These flew patrols over the central Mediterranean before reequipment at the turn of the year.
The Royal Navy's Fleet Air Arm (FAA) received more than 100 Beauforts, Numerous Beaufighter lls had been made available to 7XXseries Fleet Requirements Units, but as these proved difficult to master by pilots trained on Blenheims, an interim dual-control trainer was sought, The RAF provided six Beaufort 1As, which, after modification to FAA standard, joined 798 Sqn at Lee-on-Solent in October 1943. The unit was renumbered 762 Sqn in March 1944 and moved to Dale, converting to Beaufort T.IIA trainers, the last retiring in March 1946. The station flight at Yeovilton used three
On Malta 728 Sqn received about 15 from September 1944, retaining them for exactly a year, and 779 Sqn received two or three at Gibraltar during November 1944. Although there is no confirmation of actual receipt, 775 Sqn at Dekheila, Egypt, and 788 at Port Reitz, Kenya, also had Beauforts on their inventories.
The Turkish Air Force (TuAF) was the last service to receive Beauforts. Ordering 18 (possibly 21) in 1943, there is still doubt as to how many were received. Although RAF records list 13 M1k 1As and 12 Mk 11As supplied from North African MUs during 1944 and 1945 respectively, TuAF aircraft lists contain 46XXseries serial numbers for only 11 Mk 1As and ten M1k 11As. However, a separate list of accidents contains the serial numbers of an additional eight Beauforts, at least four of them 1As: the other four have out-of-series 59XX-range serial numbers. With no torpedoes available the Beauforts were initially used as GR bombers by two squadrons of the 105th Torpedo & Reconnaissance Group. The few M1k 11As that survived until 1947 were modified locally to trainer standard by Bristol's resident engineers and used to convert pilots on to Beaufighter M1k Xs at lzmjt. Precise dates are lacking, but all the Beauforts had gone by the end of 1950 at the very latest.
Total Beaufort production was 1380, including 700 built in Australia.