a single TB-3 4M-17F was streamlined with removal of turrets and bomb shackles, covering of all openings, and fitting of wheel spats. This resulted in only a 4.5% increase in top speed and a similar increase in the range. Tupolev concluded that streamlining was minimally beneficial for large and slow aircraft. To study the effect of corrugated skin, in January–February 1935 a single TB-3 4AM-34R had the corrugations incrementally covered with fabric. This resulted in a 5.5% gain in top speed and a 27.5% increase in the ceiling. The same aircraft demonstrated a significant increase in climb rate when fitted with experimental four-blade propellers. Record flights TB-3 4M-34R set a flight endurance record of 18 hours and 30 minutes. TB-3 4AM-34FRN with Andrey Yumashev at the controls set a number of payload-to-altitude records: 11 September 1936 – to , improved to on 28 October. 16 September 1936 – to 20 September 1936 – to Design The TB-3 was an all-metal aircraft of steel construction, as one of the designs from Andrei Tupolev's design bureau to be based on the 1918-onward all-metal aircraft design practices and technology pioneered by Hugo Junkers. The frame was composed of V-section beams covered with non-stressed corrugated skin ranging from to in thickness. The corrugations were deep and apart. The cantilever wing was supported by four tube-section spars. In 1934, thanks to the development of stronger steel alloys, the wingspan was increased from with a concurrent wing area increase from . Any part of the aircraft could be walked on in soft shoes without damaging the skin, and the leading edges of the wings swung down to form walkways for engine maintenance. Controls were cable-actuated with a variable-incidence tailplane and a trim compensation system in case of engine failures on one side. Fixed main landing gear was not fitted with brakes. The fuel tanks did not have fire or leak protection, although the engines had an internal fire-extinguishing system. The M-17 engines were tuned to provide a maximum theoretical range of without spark plug or carburetor fouling. Defensive armament consisted of light machine guns in five turrets — one in the nose, two on top of mid-fuselage, and one retractable "dustbin" under each wing between the engine nacelles. Later variants moved one of the top fuselage turrets aft of the tail fin. Operational history The TB-3 was used operationally during the Battle of Khalkhin Gol against