Bartini Stal-7


The Bartini Stal-7 was a twin-engined transport aircraft designed and produced in the Soviet Union from 1934.

Development

In 1934, Aeroflot issued a requirement for two transport aircraft types. Bartini began design work in October 1934 on an aircraft to meet the larger 10/12 passenger specification.
Flight testing began in spring 1935 piloted by Nikolai Shebanov, revealing high efficiency in speed, range and load. The aircraft was to make a trip around the world piloted by Shebanov and so it was loaded with additional equipment and an extra of fuel. By autumn 1937 it was ready to peform the trip, yet the Stal-7 crashed on take-off in 1938 during full load testing, prompting the arrest of Bartini who was imprisoned in a sharashka in Bolshevo led by fellow inmate Andrei Tupolev.
Repair of the Stal-7 was carried out under Vladimir Yermolayev's direction in 1939 and the aircraft continued to demonstrate excellent cruise performance during a, Moscow – Sverdlovsk – Sevastopol – Moscow, non-stop flight averaging on 28 August 1939.
The impressive performance of the Stal-7 prompted the appointment of Yermolayev as the head of OKB-240, to develop the Stal-7 into an effective long-range bomber, resulting in the DB-240, Yer-2 and Yer-4 aircraft.

Design

Initially, Bartini intended the Stal-7 to use a steel tube truss airframe, with fabric covering, but problems with complexity and the flexibility of the truss structure led Bartini to re-design the aircraft with a light-alloy monocoque structure.
The hydraulically retractable main undercarriage legs retracted rearwards into the engine nacelles housing Klimov M-100 or M-103 engines, which were positioned at the junction of the inverted gull wings. The trailing edges had hydraulically operated flaps inboard and ailerons outboard. Both the wings and tail surfaces were sharply tapered and the inboard wing sections sloped sharply upwards to pass through the fuselage cabin. The concave surface of the center section created an air cushion between the wings and ground, which reduced landing speed and increased horizontal speed.