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Tupolev Tu-4
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Image by Peer.Gynt
Monino Central Air Force Museum (Moscow) July 2010

The Tupolev Tu-4 (NATO reporting name: Bull) was a piston-engined Soviet strategic bomber that served the Soviet Air Force from the late 1940s to mid-1960s. It was a reverse-engineered copy of the U.S.-made Boeing B-29 Superfortress.
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 Soviet declaration of war against Japan in accordance with the Yalta agreement to enter the war within 90 days of VE day (to allow it time to move its forces from Europe to Asia) at about 11pm on August 8, 1945 — two days after the U.S. bombing of Hiroshima and the subsequent entente with Japan ending, the fourth 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 sheet aluminum in thicknesses matching the B-29’s imperial measurements were unavailable. The corresponding metric-gauge metal was of different thicknesses. 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,[9] 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.
The aircraft was first displayed during a flyover at the Aviation Day parade on 3 August 1947 at the Tushino Airport in Moscow. Three aircraft flew overhead. It was assumed that these were merely the three B-29 bombers that were known to have been diverted to the USSR during World War II. Minutes later a fourth aircraft appeared. Western analysts realized that the Soviets must have reverse-engineered the B-29. The appearance of an obviously Superfortress-derived Tu-70 transport over the crowd removed any doubt about the success of the reverse-engineering.
Eight hundred and forty-seven Tu-4s had been built when production ended in the Soviet Union in 1952, some going to China during the later 1950s. Many experimental variants were built and the valuable experience launched the Soviet strategic bomber program. Tu-4s were withdrawn in the 1960s, being replaced by more advanced aircraft: the Tupolev Tu-16 (starting in 1954) and the Tupolev Tu-95 (starting in 1956). By the beginning of the 1960s, the only Tu-4s still operated by the Soviets were used for transport or airborne laboratory purposes. A Tu-4A was the first Soviet aircraft to drop a nuclear weapon, the RDS-1.

(Post from China rapid prototyping manufacturer blog)

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