Bartini Stal-7

Stal-7
Role	Transport
National origin	USSR
Manufacturer	ZOK NII GVF
Designer	Roberto L. Bartini
First flight	Spring 1937
Number built	1
Variants	Yermolaev DB-240 Yermolayev Yer-2 Yermolayev Yer-4

The Stal-7 was a twin-engined transport aircraft designed and produced in the USSR from 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. 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, which were positioned at the junction of the inverted gull wings. The trailing edges had hydraulically operated flaps inbord 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.

Flight testing began in the Spring of 1937 piloted by N. P. Shebanov, revealing high efficiency in speed, range and load. The Stal-7 crashed on take-off during full load testing, prompting the arrest of Bartini who was sent to a gulag in Siberia.

Repair of the Stal-7 was carried out under Vladimir Yermolaev's direction in 1939 and the aircraft continued to demonstrate excellent cruise performance during a 5,068 kilometres (3,149 mi), Moscow – Sverdlovsk – Sevastopol – Moscow, non-stop flight averaging 405 kilometres per hour (252 mph).

The impressive performance of the Stal-7 prompted the appointment of Yermolaev as the head of OKB-240, to develop the Stal-7 into an effective long-range bomber, resulting in the DB-240 (Dal'niy Bombardirovschik – long-range bomber), Yer-2 and Yer-4 aircraft.

Data from Encyclopedia of Russian Aircraft 1875–1995

General characteristics

Performance

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