Tu-4

Tupolev Tu-4

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 American-made Boeing B-29 Superfortress.

Design and development

Toward 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 had the locally designed Petlyakov Pe-8 four-engined "heavy" in service at the start of the war, but only 93 had been built by the end of the war and the type had become obsolete. The U.S. regularly conducted bombing raids on Japan, from distant Pacific forward bases using B-29 Superfortresses. Joseph Stalin ordered the development of a comparable bomber.

The U.S.had refused, twice, 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 to the 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. The aircraft included 1 Boeing-Wichita −5-BW, 2 Boeing-Wichita −15-BWs and the wreckage of 1 Boeing-Renton −1-BN – three different models from two different production lines (respectively Wichita and Renton factories). Only one of the four had de-icing boots as used on the Tu-4. 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. atomic bombing of Hiroshima and the subsequent entente with Japan ending, the fourth B-29 was returned to the US along with its crew.

Stalin told Tupolev to clone the Superfortress in as short a time as possible instead of continuing with his own comparable ANT-64. The reverse-engineering effort involved 900 factories and research institutes, who finished the design work during the first year; 105,000 drawings were made. By the end of the second year, the Soviet industry was to produce 20 copies of the aircraft ready for State acceptance trials.

The Soviet Union used the metric system, so 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, yet despite these challenges the prototype Tu-4 only weighed about 340 kg (750 lb) 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.^[14] The Soviet engine, theShvetsov ASh-73 was a development of the Wright R-1820 but was not otherwise related to the B-29's Wright R-3350 — the ASh-73 also powered some of Aeroflot's remaining obsolescent Petlyakov Pe-8 airframes, an earlier Soviet four-engined heavy bomber whose production was curtailed by higher priority programs. The B-29's 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.

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.

First public appearance

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.

Operational history

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 including the Tupolev Tu-16 jet bomber (starting in 1954) and the Tupolev Tu-95 turboprop bomber (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.

Specifications (Tu-4)

General characteristics

• Crew: 11
• Length: 30.179 m (99 ft 0 in)
• Wingspan: 43.047 m (141 ft 3 in)
• Height: 8.46 m (27 ft 9 in)
• Wing area: 161.7 m² (1,741 sq ft)
• Aspect ratio: 11.5
• Empty weight: 36,850 kg (81,240 lb)
• Gross weight: 47,850 kg (105,491 lb)
• Max takeoff weight: 55,600 kg (122,577 lb) – 63,600 kg (140,214 lb)
• Powerplant: 4 × Shvetsov ASh-73TK 18-cyl. air-cooled radial piston engines, 1,790 kW (2,400 hp) each
• Propellers: 4-bladed V3-A3 or V3B-A5, 5.06 m (16 ft 7 in) diameter

Performance

• Maximum speed: 558 km/h (347 mph; 301 kn) at 10,250 m (33,629 ft)
• Range: 5,400 km (3,355 mi; 2,916 nmi) at 3,000 m (9,843 ft) with 63,600 kg (140,214 lb) take-off weight including 3,000 kg (6,614 lb) of bombs and 10% fuel reserves
• Service ceiling: 11,200 m (36,745 ft)
• Rate of climb: 4.6 m/s (910 ft/min) at 1,000 m (3,281 ft)
• Time to altitude: 5,000 m (16,404 ft) in 18.2 minutes
• Wing loading: 400 kg/m² (82 lb/sq ft)
• Power/mass: 0.11 kW/kg

Armament

• Guns:
  
• 10 × 23 mm Nudelman-Suranov NS-23 aircraft cannon, two cannon in each of the four turrets and two cannon in the tail barbette
• Missiles:
  
• 2 × KS-1 Komet standoff missiles (Tu-4K only; these anti-ship missiles resembled a scaled-down MiG-15)
• Bombs:
  
• 6 × 1,000 kg (2,200 lb) bombs

or

• 1 x RDS-1, RDS-3 or RDS-5 nuclear fission bomb (Tu-4A only)