The Armstrong Whitworth AW.55 Apollo was designed as a competitor to the Vickers Viscount in response to the requirement outlined in the wartime Brabazon Committee's Type II civil transport. It was a short- and medium-range airliner intended for operations in Europe.

Specification C.16/46 to which the Apollo was designed, called for a turboprop-powered airliner to carry between 24 and 30 passengers over a range of 1609km at 483km/h. The engine selected was the axial-flow Armstrong Siddeley Mamba, which had the advantage of commendably low frontal area compared with contemporary centrifugal-flow turboprops. However, it was of a basic type still in its design infancy, and so prone to severe teething problems. A clear example of this is seen in the case of the Mamba: in the form first used on the Apollo, the engine should have developed 1010hp plus 139kg thrust, whereas it developed only 800hp.

Right from the beginning of the design, the AW.55 (first named Achilles and Avon before finally becoming Apollo) had a span of 28.04m, but length was increased from 19.66m to 20.73m and at the production stage to 21.79m, providing accommodation for between 26 and 31 passengers seated two-abreast on each side of a central aisle.

Construction began in 1948 of two flying prototypes and a fuselage for static testing. The first prototype was given the Ministry of Supply serial VX220, and made its initial flight on April 10, 1949. Right from the beginning there were severe problems with the Mamba engines' power output and reliability, and the aircraft itself lacked longitudinal and directional stability. The control problems were remedied without undue difficulty, and the first prototype, re-registered G-AIYN, was available from October 30, 1950 for proving flights, starting with a successful flight to Paris on March 12, 1951. Finally, in July 1951, Mamba Mk 504 engines became available, but even these had severe limitations and problems. This proved the last straw, and in June 1952 further development was halted. The second prototype was subsequently completed, and both aircraft were used for a variety of experimental work for the Ministry of Supply, which had funded them. Both aircraft ended their flying lives in December 1954 when they became structural-test airframes.

3-View

A three-view drawing (496 x 743)