Avro 684
Encyclopedia
The Avro 684 was a prototype British
heavy bomber
of the Second World War
, based on Avro
's successful Lancaster
.
, Avro's chief designer, was prompted to develop the 684 design based on reports from the Royal Air Force
on their experince operating small numbers of the Boeing B-17 Flying Fortress, in this case the B-17C version. Chadwick decided to design a bomber that would dispense with defensive armament and rely on altitude and speed to evade enemy defences. The 684 was essentially identical to the Lancaster apart from the nose section which contained a pressure cabin (from the Vickers Wellington
B Mark X) and a large 'chin' mounted air intake and radiator.
The projected performance for the 684 was far beyond that of the Lancaster upon which it was based. Its cruise speed was to have been 330 mph (520 km/h) with a maximum speed of 410 mph (660 km/h), both at a height of 42,000 ft (12,800 m), absolute ceiling would have been 50,300 ft (15,330 m). A range of 2,300 mi (3,700 km) was predicted and a maximum bombload of 12,000 lb (5,400 kg) could have been carried.
To achieve this performance, Chadwick used an engine arrangement called the 'Master-Slave' layout. The four wing-mounted Rolls Royce
Merlin XX's engines were supercharged
by a fuselage-mounted slave Merlin 45 engine which drove a large, intercooled
supercharger. The Merlin 45's rpm could be adjusted so that the compressed air output from the slave's engine-driven supercharger was always at 20,000 ft (6,100 m) equivalent pressure at all altitudes between 20-40,000 ft (6,100-12,200 m), the propellors were to be four-bladed 13 ft (4 m)-diameter rotols.
Due to the pressure of constant developments to the Lancaster and design work on the York
, work on the 684 was suspended and the design was never realised.
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
heavy bomber
Heavy bomber
A heavy bomber is a bomber aircraft of the largest size and load carrying capacity, and usually the longest range.In New START, the term "heavy bomber" is used for two types of bombers:*one with a range greater than 8,000 kilometers...
of the Second World War
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, based on Avro
Avro
Avro was a British aircraft manufacturer, with numerous landmark designs such as the Avro 504 trainer in the First World War, the Avro Lancaster, one of the pre-eminent bombers of the Second World War, and the delta wing Avro Vulcan, a stalwart of the Cold War.-Early history:One of the world's...
's successful Lancaster
Avro Lancaster
The Avro Lancaster is a British four-engined Second World War heavy bomber made initially by Avro for the Royal Air Force . It first saw active service in 1942, and together with the Handley Page Halifax it was one of the main heavy bombers of the RAF, the RCAF, and squadrons from other...
.
Design
In August, Avro completed the drawings for the 684 Stratosphere Bomber, a design based on the Lancaster which had then just entered production. Roy ChadwickRoy Chadwick
Roy Chadwick, CBE, FRAeS was an aircraft designer for Avro. Born at Marsh Hall Farm, Farnworth in Widnes, son of the mechanical engineer Charles Chadwick, he was the Chief Designer for the Avro Company and was responsible for practically all of their aeroplane designs...
, Avro's chief designer, was prompted to develop the 684 design based on reports from the Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...
on their experince operating small numbers of the Boeing B-17 Flying Fortress, in this case the B-17C version. Chadwick decided to design a bomber that would dispense with defensive armament and rely on altitude and speed to evade enemy defences. The 684 was essentially identical to the Lancaster apart from the nose section which contained a pressure cabin (from the Vickers Wellington
Vickers Wellington
The Vickers Wellington was a British twin-engine, long range medium bomber designed in the mid-1930s at Brooklands in Weybridge, Surrey, by Vickers-Armstrongs' Chief Designer, R. K. Pierson. It was widely used as a night bomber in the early years of the Second World War, before being displaced as a...
B Mark X) and a large 'chin' mounted air intake and radiator.
The projected performance for the 684 was far beyond that of the Lancaster upon which it was based. Its cruise speed was to have been 330 mph (520 km/h) with a maximum speed of 410 mph (660 km/h), both at a height of 42,000 ft (12,800 m), absolute ceiling would have been 50,300 ft (15,330 m). A range of 2,300 mi (3,700 km) was predicted and a maximum bombload of 12,000 lb (5,400 kg) could have been carried.
To achieve this performance, Chadwick used an engine arrangement called the 'Master-Slave' layout. The four wing-mounted Rolls Royce
Rolls-Royce Limited
Rolls-Royce Limited was a renowned British car and, from 1914 on, aero-engine manufacturing company founded by Charles Stewart Rolls and Henry Royce on 15 March 1906 as the result of a partnership formed in 1904....
Merlin XX's engines were supercharged
Supercharger
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
by a fuselage-mounted slave Merlin 45 engine which drove a large, intercooled
Intercooler
An intercooler , or charge air cooler, is an air-to-air or air-to-liquid heat exchange device used on turbocharged and supercharged internal combustion engines to improve their volumetric efficiency by increasing intake air charge density through nearly isobaric cooling, which removes...
supercharger. The Merlin 45's rpm could be adjusted so that the compressed air output from the slave's engine-driven supercharger was always at 20,000 ft (6,100 m) equivalent pressure at all altitudes between 20-40,000 ft (6,100-12,200 m), the propellors were to be four-bladed 13 ft (4 m)-diameter rotols.
Due to the pressure of constant developments to the Lancaster and design work on the York
Avro York
The Avro York was a British transport aircraft that was derived from the Second World War Lancaster heavy bomber, and used in both military and airliner roles between 1943 and 1964.-Design and development:...
, work on the 684 was suspended and the design was never realised.