Tupolev Tu-4 - Design and Development

Design and Development

Towards the end of World War II, the Soviet Union saw the need for a strategic bombing capability similar to that of the United States Army Air Forces. The Soviet VVS air arm did have their own-design Petlyakov Pe-8 four-engined "heavy" in service at the start of the war, but only 93 were built by the end of the war as the type had been equipped with unreliable turbocharged V12 diesel engines at the start of its service to give it long range. The U.S. regularly conducted bombing raids on Japan, extremely close to the Soviet Union's borders, from distant Pacific forward bases using B-29 Superfortresses. Joseph Stalin ordered the development of a comparable bomber.

The U.S. twice refused to supply the Soviet Union with B-29s under Lend Lease. However, on four occasions during 1944, individual B-29s made emergency landings in Soviet territory and one crashed after the crew bailed out. In accordance with the Soviet–Japanese Neutrality Pact, the Soviets were neutral in the Pacific War and the bombers were therefore interned and kept by the Soviets. Despite Soviet neutrality, America demanded the return of the bombers, but the Soviets refused. Three repairable B-29s were flown to Moscow and delivered into Tupolev OKB. One B-29 was dismantled, the second was used for flight tests and training, and the third one was left as a standard for cross-reference. With the Russian declaration of war against Japan and the subsequent entent with Japan ending, a fifth B-29 was returned to the US along with its crew.

Stalin tasked Tupolev with cloning the Superfortress in as short a time as possible instead of continuing with his own comparable ANT-64 or samolet (aircraft) 64, and Soviet industry was to produce 20 copies of the aircraft ready for State acceptance trials in just two years.

The Soviet Union used the metric system, thus 1/16 inch (1.5875 mm) thick sheet aluminum and proper rivet lengths were unavailable. The corresponding metric-gauge metal was of different thicknesses and alloys and other materials new to the Soviet Union had to be brought into production. Extensive re-engineering had to take place to compensate for the differences, and Soviet official strength margins had to be decreased to avoid further redesign, yet despite these challenges the prototype Tu-4 only weighed about 750 lb (340 kg) more than the B-29, a difference of less than 1%.

The engineers and suppliers of components were under pressure from Tupolev, Stalin and the government to create an exact clone of the original B-29 to facilitate production and Tupolev had to overcome substantial resistance in favor of using equipment that was not only already in production but in some cases better than the American version. Each component made and each alteration was scrutinized and was subject to a lengthy bureaucratic process. Differences were limited to the engines, the defensive weapons, the radio (a later model used in lend-lease B-25s was used in place of the radio in the interned B-29s) and the identification friend or foe (IFF) system – the American IFF being unsuitable. The Soviet engine, the Shvetsov ASh-73 was a development of the Wright R-1820 but was not otherwise related to the B-29s Wright R-3350. and the remote-controlled gun turrets were redesigned to accommodate the harder hitting and longer ranged Soviet Nudelman NS-23 23mm cannon. Kerber, Tupolev's deputy at the time, recalled in his memoirs that engineers needed authorization from a high-ranking general to use Soviet-made parachutes. Additional changes were made as a result of problems encountered during testing, related to engine and propeller failures and equipment changes were made throughout the aircraft's service life. Although it has been widely quoted, the Tu-4 did not have a random hole drilled in the wing either to emulate a bullet hole or because a Boeing engineer made a mistake – the Russians had three complete aircraft and the wreckage of a fourth and the likelihood of all four having a hole in the same place is too small to be credible. The aircraft included 1 Boeing-Witchita −5-BW, 2 Boeing Witchita −15-BWs and the wreckage of 1 Boeing-Renton −1-BN – three different models from two different production lines. Only one of the 4 had de-icing boots as used on the Tu-4.

The Tu-4 first flew on 19 May 1947, piloted by test pilot Nikolai Rybko. Serial production started immediately, and the type entered large-scale service in 1949. Entry into service of the Tu-4 threw the USAF into a panic, since the Tu-4 possessed sufficient range to attack Chicago or Los Angeles on a one-way mission, and this may have informed the maneuvers and air combat practice conducted by US and British air forces in 1948 involving fleets of B-29s. Some attempts to develop midair refueling systems were made to extend the bomber's range, but these were fitted to only a few aircraft.