The Avro Type 621 Tutor is a two-seat British radial-engined biplane from the interwar period. It was a simple but rugged basic trainer that was used by the Royal Air Force as well as many other air arms worldwide.
Design and development
The Avro Model 621 was designed by Roy Chadwick as an Avro private venture metal replacement for the Avro 504. Conceived as a light initial pilot trainer, the biplane design featured heavily staggered equal-span, single-bay wings; the construction was based on steel tubing (with some wooden components in the wing ribs) with doped linen covering. A conventional, fixed divided main undercarriage with tailskid was used in all but the latest aircraft, which had a tailwheel.

The Model 621 was powered either by a 155 hp (116 kW) Armstrong Siddeley Mongoose or Armstrong Siddeley Lynx IV (180 hp/130 kW) or IVC (240 hp/179 kW) engine; later Lynx-powered models had the engine enclosed in a Townend ring cowling. The Mongoose-powered version was called the 621 Trainer and the more numerous Lynx-engined aircraft the Tutor. The Tutor also differed by having a more rounded rudder.

The first flight of the prototype G-AAKT was in September 1929, piloted by Avro chief test pilot Captain Harry Albert "Sam" Brown.
Operational history
Production was started against an order for three Tutors from the Irish Free State and 21 Trainers from the Royal Air Force. The RAF required a replacement for the wooden Avro 504, and after three years of trials against other machines such as the Hawker Tomtit it was adopted as their basic trainer, supplanting the 504 in 1933 and remaining in this role until 1939. As well as the first batch of 21 Trainers, a total of 381 Tutors and 15 Avro 646 Sea Tutors were eventually ordered by the RAF. RAF units to operate the type in quantity included the Royal Air Force College, the Central Flying School and Nos. 2, 3, 4 and 5 Flying Training Schools.

Subsequently, the Model 621 achieved substantial foreign sales. A.V. Roe and Co exported 29 for the Greek Air Force, six for the Royal Canadian Air Force, five for the Guangxi AF, three for the Irish AF (where it was known as the Triton) and two for each of the South African and Polish AFs. In addition 57 were licence-built in South Africa, and three licence-built by the Danish Naval Shipyard.

A total of 30 Tutors were exported to the Greek Air Force and at least 61 were licence-built in Greece by KEA. A number of Greek Tutors was incorporated in combat squadrons after Greece's entrance in WWII, used as army cooperation aircraft.

Known for its good handling, the type was often featured at air shows. Over 200 Avro Tutors and five Sea Tutors remained in RAF service at the beginning of the Second World War.

The 621 was designed as a military trainer and few reached the civil registers. In the 1930s, in addition to ten prototypes and demonstrators, two were used by Alan Cobham's Flying Circus and two trainers were retired from the RAF into private use. One 621 was used from new by Australian National Airways. After the war another four ex-RAF 621s appeared on the civil register.
Variants
Avro 621 Trainer (Mongoose powered)
Two-seat primary training aircraft.
Avro 621 Tutor (Lynx powered)
Two-seat primary training aircraft.
Avro 621 Tutor II
One aircraft was modified into a two-bay biplane.
Avro 623
Three-seat version of the Type 621 Tutor upgraded for use in Tanganyika as aerial survey aircraft. Three were built between May and December 1930 and issued to the Director of Surveys of Tanganyika. Powered by a 240 hp Armstrong-Siddeley Lynx IV.
Avro 646 Sea Tutor
Two-seat seaplane fitted with twin floats, 15 built
PWS-18
Polish-built licence version with wooden wings and Wright J-5 engine. 40 bulit
















General characteristics
Crew: 2
Length: 26 ft 4.5 in (8.039 m)
Wingspan: 34 ft 0 in (10.36 m)
Height: 9 ft 7 in (2.92 m)
Wing area: 301 sq ft (28.0 m2)
Empty weight: 1,844 lb (836 kg)
Gross weight: 2,493 lb (1,131 kg)
Powerplant: 1 × Armstrong Siddeley Lynx IVC 7-cylinder air-cooled radial piston engine, 240 hp (180 kW)
Propellers: 2-bladed fixed-pitch propeller
Performance
Maximum speed: 120 mph (190 km/h, 100 kn)
Cruise speed: 97 mph (156 km/h, 84 kn)
Range: 250 mi (400 km, 220 nmi)
Service ceiling: 16,000 ft (4,900 m)
Rate of climb: 910 ft/min (4.6 m/s)
(Text from Wikki)