Customers saw the aircraft as little more than a pressurised DC-4 Skymaster, and few orders were forthcoming, important customers preferring to buy US aircraft. The tailwheel undercarriage layout was also dated and a disadvantage. 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. 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 passenger capacity of the Avro 688 was considered unsatisfactory, so a larger version was planned from the outset. Designated the Avro 689 (also Avro XXI), the Tudor II was designed as a 60-seat passenger aircraft for BOAC, with the fuselage lengthened to 105 ft 7 in (32.18 m) compared to the Tudor I's 79 ft 6 in (24.23 m) and the fuselage increased by 1 ft (0.30 m) to 11 ft (3.4 m) diameter, making it the largest UK airliner at the time. At the end of 1944, while it was still in the design stage, BOAC, Qantas and South African Airways decided to standardise on the Tudor II for Commonwealth air routes, and BOAC increased its initial order for 30 examples to 79. There were 9 versions of the Tudor plus 3 freighter versions. Tudor 9 was fitted with four jet engines, paired in two streamlines nacelles. This was later converted to tricycle undercarriage as the Avro Ashton. The Ashton, four of which were built, was not intended for commercial use, instead as an experimental aircraft, and was used as a testbed for jet engines slung beneath the fuselage. Further details of the development of the Tudor can be found here. The specifications below are for the original Avro 688 Tudor 1 Series. Tudor 1 Series Tudor 2 Series Jet powered Tudor 9 Ashton. (Note jet enginge slung below fuselage for testing.)
