The K-5 was a scaled up version of the K-4 and was used by Dobrolet on its services within the USSR. The K-5, which was Kalinin’s outstanding design, had an enclosed two seat crew cabin forward of the wing leading edge and an eight-seat passenger cabin. Production was an impressive 260, terminating in 1934, and installed powerplants included the 335-kW (450- hp) M-15 (Bristol Jupiter built under licence), 358-kW (480-hp) M-22 introduced in 1931, and the M-17F of 544 kW (730 hp) in final series aircraft. Widely used on passenger services within the Soviet Union, some K-5s were still flying in 1940. Wing span was 20.50 m (67 ft 3 in), and with the M-17F engine maximum take-off weight was 4030 kg (8,884 lb) and maximum speed 209 km/h (130 mph).

A prolific designer of light transport aircraft in the time up to his arrest in 1938, Konstantin Alekseevich Kalinin was an early adherent of the elliptical wing planform and careful streamlining, and these features mark most of the 16 aircraft designed by Kalinin up to 1938. Designed as a feederliner for the Ukrainian operator Ukrvozdukhput and the national carrier Dobrolet, the K-4 appeared in 1928, and was reportedly powered in its prototype form by the 300-hp BMW VI V-12. The design capitalized on the best features of the earlier K-1, K-2 and K-3 light transports, which were strut-braced high-wing monoplanes with engines in the 170- to 240-hp range and able to accommodate three or four passengers.

Russian aircraft design at the time was fairly innovative, and the K-4 reflected this. The wings were of advanced elliptical planform and built of alloy with a light alloy covering; the fuselage, on the other hand, was of metal structure with metal skinning as far aft as the rear of the passenger compartment, with the tail section built of wood and covered with plywood and fabric. The pilot’s cockpit, just under the wing leading edge, was open, but the extensively glazed passenger cabin for four to six travellers was enclosed.

In production form the passenger variant was normally powered by the 240-hp BMW IV inline, though some of the ambulance variants appear to have 290-hp M-6 V-8s (licence-built HispanoSuizas) or 310-hp Junkers L 5 inlines.

Production of the K-4 was only on a limited scale compared with that of its successor, the somewhat larger K-5, of which about 260 seem to have been built between 1930 and 1934. Spanning 20.5 m (67 ft 3 in) compared with the K-4′s 16.72 m (54ft 10 in), the K-5 was essentially a scaled-up model of the earlier type, with a crew of two and accommodation for up to eight passengers. The prototype was powered by a 525-hp M-15 radial (licence built Bristol Jupiter), and may have been reengined with a Pratt & Whitney Hornet of the same power, but the engines favoured in production K-5s were the 500-hp M-17F or 480-hp M22. Although an enclosed cockpit for the two crew was provided, the wings reverted to the otherwise obsolescent construction of wooden structure with fabric covering, though the planform of this and the tailplane were the ellipses seen in the K-4.

Maker: K A Kalinin Design Bureau

Span: 16.72m (54ft l0in)

Length: 11.35m (37ft2 ¾ in)

Height: not available

Wing area: 40 m2 (430 ½ Sq ft)

Weight: maximum 2400 kg (5291Ib); empty 1400 kg (3086Ib)

Powerplant: one 240-hpBMW IV 6-cylinder water cooled inline engine

Performance: cruising speed 160km!h (99 mph); range not available

Payload: seats for up to 6 passengers

Crew: 1

Production: approx 22