Avro Tudor

The Avro Type 688 Tudor was a British piston-engined airliner based on Avro's four-engine Lincoln bomber, itself a descendant of the famous Lancaster heavy bomber, and was Britain's first pressurised airliner. Customers saw the aircraft as little more than a pressurised DC-4, and few orders were forthcoming, important customers preferring to buy US aircraft. The tailwheel undercarriage layout was also dated and a disadvantage.

Avro began work on the Type 688 Tudor in 1943, following Specification 29/43 for a commercial adaptation of the Lancaster IV bomber, which was later renamed Lincoln. The specification was based on recommendations of the Brabazon Committee, which issued specifications for nine types of commercial aircraft for postwar use.

Avro first proposed to build the Avro 687 (Avro XX), which was a Lincoln bomber with a new circular section pressurized fuselage and a large single fin and rudder in place of the predecessor's double ones. During the design stage, the idea of a simple conversion was abandoned and the Avro 688 was designed, which retained the four Rolls-Royce Merlin engines. It was designed by Roy Chadwick who, due to wartime restrictions, could not design a completely new aircraft, but had to use existing parts, tools and jigs. Using the Lincoln's wing, Chadwick, who had worked on the Lancaster, designed the Tudor to incorporate a new pressurized fuselage of circular cross-section, with a useful load of 3,765 lb (1,705 kg) and a range of 3,975 mi (6,400 km).

Two prototypes were ordered in September 1944 and the first, G-AGPF, was assembled by Avro's experimental flight department at Manchester's Ringway Airport and first flew on 14 June 1945. It was the first British pressurised civilian aircraft, although the prototype initially flew unpressurised. The prototype Tudor I had 1,750 hp (1,305 kW) Rolls-Royce Merlin 102 engines, but the standard engines were 1,770 hp (1,320 kW) Merlin 621s.

The Tudor was a low-wing cantilever monoplane with four engines, a single fin and rudder and a retractable tailwheel undercarriage (in its original configurations).

The wing was of NACA 23018 section at the root, and was a five-piece, all-metal, twin-spar structure. The untapered centre section carried the inboard engines and main undercarriage, while the inner and outer sections were tapered on their leading and trailing edges, with the inner sections carrying the outboard engines. The ailerons were fitted with trim and balance tabs, and there were hydraulically operated split flaps in three sections on each side of the trailing edges of the centre section and inner wings. A 3,300 imp gal (15,000 L; 4,000 US gal) fuel capacity was given by eight bag tanks, one on either side of the fuselage in the centre section and three in both inner wings.

The all-metal tail unit had a dorsal fin integrated with the fuselage, and a 43 ft (13 m) twin-spar tailplane with inset divided elevators. The control surfaces were mass-balanced, and each had controllable trim and servo tabs.

The circular cross-section fuselage was an all-metal semi-monocoque structure, of 10 ft (3.0 m) diameter, fitted with kapok noise insulation above floor level. The hydraulically operated main-wheel units were similar to those of the Lancaster, had single Dunlop wheels and retracted rearward into the inboard engine nacelles. The twin tailwheels retracted rearward into the fuselage and were enclosed by twin longitudinal doors.