Stal-6, EI by R.L.Bartini

24k Stal-6 from "History of aircraft construction in the USSR", Vol.1 p.471

Experimental fighter, far ahead of its time. Leaving alone its steel (so Stal) construction, following features are to be mentioned:

• Extremely clean shapes - pilot's cockpit was flush with top of the fuselage!
• Material chosen to provide minimal possible weight: chromium-molibdenium steel tube frame, aluminum/magnesium alloys (AltMag, Electron) used for front section skin (integrating oil tanks), thin steel tube bundles as a wing structure with thin stainless steel skin, plywood skin on the tail.
• Single-wheel landing gear with tail skid and small stabilizing skis on the wing tips. ALL landing gear elements are completely retractable. At the time world new only semi-retractable gear with wheels going backwards and half-hide in the wing.
• Water evaporative cooling system inside the wing surface, like in some racer aircraft.
• Elevator controls had adjustable reduction number, allowing pilot to adjust force on the control stick depending on the aircraft speed and flight conditions. This system was 'invented' again in 1944 by TsAGI and LII...

Stal-6 successfully passed all tests during Fall 1933. Pilots A.B.Yumashev and P.M.Stefanovskij proved that 'one-wheel' landing gear is as good as conventional on takeoff, landing and taxi. Speed on ground level was 420km/h, 150km/h faster than typical speed of contemporary fighters.

Interestingly, that VVS authority already pushed aircraft builders to increase speed of their aircraft, but faced 'organised resistance'. Manufacturers did not believe that substantial speed increase is possible in short time. They interpreted rumors about Stal-6 as a 'duck'.

68k drawing Stal-6/8 from 'Krylia Rodiny' magazine, courtesy of

On official meeting with K.E.Voroshilov and G.K.Ordzhonikidze representative of the GUAP tried to prove that fighter with speed 400-450km/h is impossible. He was corrected that such aircraft (Stal-6) already exists and its designer (R.L.Bartini) is present on the meeting.

GVF received an order to build fighter based on Stal-6 design. Project was designated Stal-8...

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There was a widely used argument against evaporative cooling systems - vulnerability. But... this is a common feature of water-cooled engines (except special cases with armor-shielded cooler like Il-2). Large area of cooling surface is not a weakness - higher probability of combat damage is compensated by relatively lower impact of a hole on the system.

During trials of Stal-6 A.B.Yumashev performed few flights with imitation of a cooler combat damage. Each flight lasted more than 30min! Taking into account that flight endurance of (most) Soviet WW-II single-engine fighters was close to 1hour, damaged fighter could not only return home safely, but do it after the fight is over.

There also was a room for improvement - Stal-6 had single-unit cooler, while segmented system could be even less sensitive to damage.

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References:
• "History of aircraft construction in the USSR", Vol.1 p.471-472;
• "Most cherez vremja" (Bridge across the time)

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More Links...
• Stal-6, Bartini
• Stal-6 for FSim by A.Belov