From (surprise surprise) Tony Buttler’s British Secret Projects – Fighters and Bombers 1935-1950
In August 1941 Avro completed a brochure for its Type 684 Stratosphere Bomber. This all-metal airplane was designed to operate at a height that made it immune from fighter or AA interference and, with the exception of the nose portion of the fuselage, was identical to the Lancaster. The nose contained a pressure cabin, as designed for the experimental high-altitude Vickers Wellington flown in September 1940, which in conjunction with a Rotol blower, would maintain air conditions corresponding to 10,000ft when flying at an altitude of 40,000ft. To achieve this high-altitude flight the air flowing to the carburettors of the four wing-mounted Merlins would be increased in pressure by a slave Merlin 45 housed within the fuselage between and above the wing spars (the blower was placed between and above the rear spar). By regulating the rpm of the slave-blower to suit the prevailing conditions its discharge pressure could be made to correspond to 20,000ft conditions at all heights between 20,000ft and 40,000ft.
The 684 could carry either 4,000lb; 8,000lb or 12,000lb bombs, average cruise would be about 320mph and range 2,300 miles. The service ceiling at the start of the mission was 42,000ft and at the end of a flight 49,600ft. The absolute ceiling was 50,300ft, sea-level rate of climb at 60,000lb was 940ft/minute and at 38,492lb 1,910ft/min, time to 40,000ft was 57 minutes. A total of 2,130 gal of fuel was carried in the wings. The development workload needed for the standard Lancaster and its variants, and the new Avro 685 York transport which used the same mainplane, power eggs, tail and undercarriage, led to the design work on the 684 being suspended.
Dimensions: Span 103.2ft, length 72ft, WA 1,297 square feet,
Powerplant: 4 x Merlin XX, 1 x Merlin 45 (slave)
Performance: Max Speed 410mph at 42,500ft.
Armament: 12,000lb, no defensive armament carried.
