Bartini Stalf-7

Purpose: Originally, fast passenger transport; later, long-range experimental aircraft.

Design: SNII GVF; construction at GAZ (Factory) No 81, Moscow Tushino.

In the winter 1933-34 the GUGVF (chief ad­ministration of the civil air fleet) issued a re­quirement for a fast transport aircraft to carry 10 to 12 passengers. Curiously, the two proto­types built to meet this demand were both the work of immigrant designers, the Frenchman Laville (with ZIG-1) and the Italian Bartini. The latter had already produced drawings for a transport to cruise at 400km/h (248mph), which was well in advance of what the GVF had in mind. Always captivated by speed, Stalin decreed that a bomber version should be designed in parallel. Still in charge of de­sign at the SNII GVF, Bartini refined his study into the Stal’-7, the name reflecting its steel construction.

Strongly influenced by the Stalin decree, Bartini created a transport notable for its cramped and inconvenient fuselage, highly
unsuitable for passengers but excellent for bombs, and for long-range flight. The original structure was to be typical Bartini welded steel-tube trusses with fabric covering, but the stress calculations were impossibly diffi­cult, with 200 primary rigid welded intersec­tions between tubes of different diameters. In late 1934 the fuselage was redesigned as a light-alloy stressed-skin structure, with sim­pler connections to the unchanged wing.

Only one aircraft was built, in the work­shops ofZOK, the factory for GVF experimen­tal construction. The first flight was made on an unrecorded date in autumn 1936, the pilot being N P Shebanov. Performance was out­standing, and Shebanov proposed attempting a round-the-world flight. In 1937 the StaP-7 was fitted with 27 fuel tanks with a total ca­pacity of 7,400 litres (1,628 Imperial gallons, 1,955 US gallons). A maximum-range flight was then attempted, but – possibly because of structural failure of a landing gear – the air­craft crashed on take-off. Bartini was arrest­ed, and was in detention (but still designing, initially at OKB-4, Omsk) for 17 years.

The aircraft was repaired, and on 28th Au­gust 1939, at a slightly reduced weight, suc­cessfully made a closed-circuit flight of 5,068km (3,149 miles) in 12hrs Slmin (aver­age speed 404.936km/h, 251.62mph), to set an FAI Class record. The route was Moscow Tushino-Maloe Brusinskoe (Sverdlovsk re – gion)-Sevastopol-Tushino, and the crew comprised Shebanov, copilot VAMatveyev and radio/navigator N A Baikuzov. In Bartini’s absence, the project was seized by his op­portunist co-worker V G Yermolayev, who re­designed it into the outstanding DB-240 and Yer-2 long-range bomber.

The wing was typical Bartini, with pro­nounced straight taper and construction from complex spars built up from multiple steel tubes, almost wholly with fabric covering. Each wing comprised a very large centre sec­tion, with depth almost as great as that of the fuselage, terminating just beyond the engine nacelles 2.8m (9ft 2/4in) from the centreline, with sharp anhedral, and thinner outer panels with dihedral. The trailing edges carried split flaps and Frise ailerons, the left aileron having

a trim tab. One account says that the inverted – gull shape ‘improved stability and provided a cushion effect which reduced take-off and landing distance’, but its only real effect was to raise the wing on the centreline from the low to the mid position.

This was just what the fuselage did not need, because the massive deep spars formed almost impassable obstructions and eliminated any possibility of using the aircraft as a passenger airliner. The fuselage was a light-alloy structure, with an extremely
cramped cross-section with sides sloping in towards the top (almost a round-cornered tri­angle). Entry was via a very small door on the left of the rear fuselage. The cockpit in the nose seated pilots side by side, and had a glazed canopy with sliding side windows and the then-fashionable forward-raked wind­screen. Immediately behind the cockpit there was a station for the navigator/radio operator. The tail surfaces, made of dural/fabric, were of low aspect ratio, the elevators having tabs.

The engines were the 760hp M-100, these being the initial Soviet licence-built version derived by V Ya Klimov from the Hispano – Suiza 12Ybrs. They were installed in neat cowlings at the outer ends of the centre sec­tion, angled slightly outwards and driving pro­pellers with three metal blades which could have pitch adjusted on the ground. One ac­count states that wing-surface radiators were used, but it is obvious from photographs that ordinary frontal radiators were fitted, as in the Tupolev SB bomber. Plain exhaust stubs were fitted, though this may have scorched the wing fabric and one drawing shows ex­haust pipes discharging above the wing. In the course of 1938-39 the original engines were replaced by the derived M-103, rated at 860hp, which improved performance with heavy fuel loads. A hydraulic system was pro­vided to operate the flaps and the fully re­tractable main landing gears, each unit of which had a strong pair of main legs which hinged at mid-length, the unit then swinging back on twin forward radius arms (like a DC – 3 back-to-front). The castoring tailwheel was fixed. In the nose were twin landing lights.

The Stal’-7 was simply a sound aeroplane able to fly at what was in its day a very long way at high speed. As a transport it was in­convenient to the point of being useless, though it was supposed to be able to seat 12 passengers, and it was flawed by its basic lay­out and structure. The Soviet Union was right to take a licence for the Douglas DC-3. On the other hand, Yermolayev transformed the Stal’-7 into an outstanding long-range bomber.

Left: Two views of Stal’-7.