keskiviikko 7. joulukuuta 2016

Avro Manchester

The Avro 679 Manchester was a British twin-engine heavy bomber developed during the Second World War by the Avro aircraft company in the United Kingdom. Serving in the Royal Air Force and Royal Canadian Air Force, the Manchester was an operational failure because of its underdeveloped, underpowered and unreliable engines. The aircraft was the forerunner of the successful four-engined Avro Lancaster, which would become one of the most capable British strategic bombers of the war.

The Manchester was originally designed to the Air Ministry Specification P.13/36; it was the same specification that Handley Page also followed in their design of the Halifax bomber. Issued in May 1936, Specification P.13/36 called for a twin-engine monoplane "medium bomber" for "worldwide use", which was to be capable of carrying out shallow (30°) dive bombing attacks and carry heavy bombloads 3,630 kg or two 460 mm torpedoes. Provision for catapult assisted takeoff to permit the maximum load was also part of the specification, although the need for this provision was explicitly removed in July 1938. Cruising speed was to be a minimum of 275 mph at 15,000 feet. The Air Ministry had expectations for an aircraft of similar weight to the B.1/35 specification, but being both smaller and faster.

Avro had already started work on a design before the invitation to tender. They were in competition with Boulton Paul, Bristol, Fairey, Handley Page and Shorts. Vickers had the Warwick with Napier Sabre engines but did not tender it. In early 1937, the Avro design and the rival Handley Page HP.56 were accepted and prototypes of both ordered; but in mid-1937, the Air Ministry exercised their rights to order "off the drawing board". This skipping of the usual process was necessary due to the initiation of a wider expansion of the RAF in expectation of war. From 1939, it was expected that the P.13/36 would replace existing medium bombers, such as the Armstrong Whitworth Whitley, Handley Page Hampden and Vickers Wellington.

The design used the Rolls-Royce Vulture 24-cylinder X-block engine, which was two Rolls-Royce Peregrine Vee cylinder blocks mounted one on top of the other, the bottom one inverted to give the "X" shape. When developed in 1935, the Vulture engine had promise - it was rated at 1,760 hp (1,310 kW) but it proved woefully unreliable and had to be derated to 1,480 - 1,500 hp . Avro's prototype Manchester L7246, was assembled by their experimental department at Manchester's Ringway Airport and first flew from there on 25 July 1939, with the second aircraft following on 26 May 1940.

The Vulture engine was chosen by Avro and not stipulated by the Air Ministry as is sometimes claimed; other engine layouts considered included the use of two Bristol Hercules or Bristol Centaurus radial engines. The Handley Page HP.56, always intended as the backup to the Avro, was redesigned to take four engines on the orders of the Air Ministry in 1937, when the Vulture was already showing problems.

While the Manchester was designed with a twin tail, the first production aircraft, designated the Mk I, had a central fin added and twenty aircraft like this were built. They were succeeded by the Mk IA which reverted to the twin-fin system but used enlarged, taller fin and rudders mounted on a new tailplane, with span increased from 6.7 - 10 m. This configuration was carried over to the Lancaster, except for the first prototype, which also used a central fin and was a converted, unfinished Manchester. Avro constructed 177 Manchesters while Metropolitan-Vickers completed 32 aircraft. Plans for Armstrong Whitworth and Fairey Aviation at Stockport/Ringway to build the Manchester were abandoned. Fairey's order for 150 Manchesters was replaced by multiple orders for the Handley Page Halifax.

The forward section of a Manchester Mark I at Waddington, Lincolnshire, showing the nose with the bomb-aimer's window, the forward gun-turret and the cockpit, September 1941
The Avro Manchester was designed with great consideration for ease of manufacture and repair. The fuselage of the aircraft comprised longitudinal stringers or longerons throughout, over which an external skin of aluminium alloy was flush-riveted for a smooth external surface. The wings were of a two-spar construction, the internal ribs being made of aluminium alloys; fuel was contained with several self-sealing fuel tanks within the wings. The tail shared a similar construction to the wing, featuring a twin fin-and-rudder configuration that provided good vision for the dorsal gunner.

The cockpit housed the pilot and fighting controller's position underneath the canopy, and these two crew members were provided with all-round vision. The navigator was seated aft of the fighting controller and the position included an astrodome for use of a sextant. The bomb aimer's station was housed inside the aircraft's nose, beneath the forward turret and bomb aiming was conducted using optical sights housed in this compartment. For crew comfort on lengthy missions, a rest area was situated just to the rear of the main cabin.

The aircraft's undercarriage was entirely retractable via hydraulic systems, or in an emergency, a backup air system. The doors to the bomb bay were also operated by these systems, an additional safety measure was installed to ensure that the bombs could not be dropped if the doors were shut. The bombs were housed on bomb racks inside the internal bomb bay, and other armaments such as torpedoes could also be fitted. All fuel tankage was located in the wings in order to keep the fuselage free to accommodate more armaments in the bomb bay which covered nearly two-thirds of the underside of the fuselage.

Vulnerable parts of the aircraft were armoured; the pilot had additional armour and bulletproof glass and an armoured bulkhead was to the rear of the navigator's position. The Manchester featured three hydraulically-operated turrets, located in the nose, rear and mid-upper fuselage; the addition of a ventral turret directly behind the bomb bay had been considered and tested on the second prototype, but did not feature on production aircraft. Access to all crew stations was provided by a walkway and crew positions had nearby escape hatches.

The Manchester was powered by a pair of Vulture engines; in service these proved to be extremely unreliable. Aviation author Jon Lake stated of the Vulture: "The engine made the Manchester mainly notable for its unreliability, poor performance, and general inadequacy to the task at hand" and attributed the aircraft's poor service record to the engine troubles.

I was one of the six original pilots to have flown with the first Manchester squadron. That was a disaster. The aircraft itself, the airframe, had many shortcomings in equipment in the beginning, but as we found out Avro were excellent in doing modifications and re-equipping the aeroplane. The engines never were and never did become reliable. They did not give enough power for the aeroplane, so we ended up with two extremely unreliable 1,750 hp engines having to haul a 50,000-pound aircraft. We should really have had 2,500 hp engines. You felt that if you'd lost one, that was it, you weren't coming home. It didn't matter if you feathered the propeller or not. There was only one way you went and that was down. I have seen an aircraft doing a run up on the ground and have two pistons come right out through the side of the engine. The original bearings were made without any silver as an economy measure, so they weren't hard enough. The bearings would collapse the connecting rod and the piston would fling out through the side of the engine and bang! Your engine just destroyed itself.

On 5 August 1940, the first production Avro Manchester, L7276, was delivered to RAF Boscombe Down in advance of service acceptance trials. In November 1940, the Manchester officially entered service with the newly reformed No. 207 Squadron of RAF Bomber Command. The type passed all acceptance tests by 21 December 1940, and 207 Squadron had at least 80 Manchesters on strength by the end of 1940. The Manchester's first operational mission was conducted on 24 - 25 February 1941 in a raid on the French port of Brest. On 13 March 1941, L7319 became the first Manchester to be shot down by enemy fire.

On 13 April 1941, all Manchesters were temporarily grounded due to a higher than expected number of engine bearing failures; on 16 June 1941, a second grounding of the type was ordered due to continuing engine troubles. The unservicability of the Vulture engine forced squadrons to make use of obsolete bombers such as the Handley Page Hampden in its place. Upon the restart of operations in August 1941, additional issues with the aircraft were encountered; the problems included excessive tail flutter, hydraulic failures, and faulty propeller feathering controls. Production of the Manchester was halted in November 1941, by which point a total of 209 aircraft had entered service with the RAF. A total of eight bomber squadrons were equipped with the type, it also served in two further squadrons and also saw use by RAF Coastal Command.

While modifications were made by Avro to address some of the technical issues experienced, unit strength suffered and Bomber Command was frequently unable to raise significant numbers of aircraft to participate in large scale bombing missions; on 7 November 1941, all of the RAFs serviceable bombers had been dispatched to bomb Berlin, out of a force of over 400 bombers, only 15 were Manchesters. On 3 March 1942, out of a force of nearly 200 bombers sent against a Renault factory near Paris, 25 were Manchesters while during the first 1,000 bomber raid on Cologne on 30 May 1942, 35 Manchesters were amongst the 1,047 bombers sent to attack the city. Flying Officer Leslie Manser was posthumously awarded the Victoria Cross for his actions while piloting Manchester L7301 of 50 Squadron during the Cologne bombing mission.

The Mk III Manchester (serial number BT308) which first flew on 9 January 1941, was essentially the first Lancaster, featuring a longer wing fitted with four Rolls-Royce Merlins in new power-egg nacelles - originally developed by Rolls-Royce for the Merlin-powered Beaufighter II - although initially retaining the three fins and twin outboard rudders (the central fin had no movable control surface) of the Manchester I. BT308 received the "Lancaster" name immediately after its first flight. The second prototype Lancaster DG595 featured the twin, enlarged fins and rudders of the Manchester IA. Manchester production continued until November of that year but some aircraft that were still in production were instead completed as Lancasters.

The 193 operational Manchesters flew 1,269 sorties with Bomber Command, dropping 1,657 tonnes of bombs and lost 78 aircraft in action, flying its last operation against Bremen on 25 June 1942. A further 45 were non-operational losses of which 30 involved engine failure. The Manchester was withdrawn from operations in mid-1942 in favour of more capable aircraft. Its final role in RAF service was as instructional trainers for converting crews to the RAF's new Lancaster bombers; the Manchester and Lancaster shared nearly identical crew positions and fuselages. The type persisted in use for training purposes into 1943 before being completely retired.

Royal Canadian Air Force
Royal Air Force

Specifications Manchester Mk I
Crew: 7
Length: 21.34 m
Wingspan: 27.46 m
Height: 5.94 m
Wing area: 105.1 m²
Empty weight: 14,152 kg
Max. takeoff weight: 22,680 kg
Powerplant: 2 × Rolls-Royce Vulture I 24-cylinder X-type, 1,760 hp (1,310 kW) each
Maximum speed: 426 km/h at  5,200 m
Range: 1,930 km with maximum bomb load of 4,695 kg
Service ceiling: 5,850
Armament: 8 × 7.7 mm Browning machine guns, nose (2), dorsal (2) tail (4) turrets
Bombs: 4,695 kg bomb load

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