Aircraft Focus
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The subject of this Aircraft Focus is the "Soviet Superfortress"; the Tupolev Tu-4 (ASCC code name 'Bull'), unlicenced copy of the US Boeing B-29 bomber.
One of only three complete surviving Tu-4s and the only one in its homeland, s/n 2805103 '01 Red' is on display at the Central Russian Air Force Museum at Monino, Moscow. This aircraft took part in an aborted bombing raid launched from Borispyl Airport, Kiev to bomb Budapest, Hungary at the height of the 1956 anti-communist uprising. The Tu-4 could carry an offensive load of over 26,000lbs (11,793.4kgs) in two payload bays located in the centre fuselage, or Section F-3, which were enclosed by two outward opening doors per bay. For long range operations, fuel cells could be mounted in the forward bomb bay. A variety of bomb sizes could be carried, from FAB-50 (the bomb number designated the weight in kilograms - 110.23lbs) to FAB-3000M46 (6613.867lbs) bombs, which were mounted on a variety of bomb racks depending on the size and type of load carried, or whether mixed or not. Bomb release could be carried out by the bombardier, aircraft captain or radar operator and could be dropped singly, in series of one, two or four, or in a salvo by means of the ESBR-45 electric bomb release mechanism. Exterior signal lighting from the lead aircraft enabled others to drop on command to avoid breaking radio silence. In visual meteorological conditions (VMC), an OPB-4S or OPB-5SN optical bombsight, the latter in aircraft built in the Moscow plants. Data from the bombsight was fed to the AP-5 autopilot, enabling the bombardier to take control of the aircraft during the bombing run. In IMC the bombardier worked closely with the radar operator via radio, using the Kobal’t ground mapping radar, although the radar operator had the means to carry out the bombing run independently of the bombardier.
Soviet knowledge of the Boeing B-29 Superfortresses' existence came in 1943 from Great War ace Capt. Eddie Rickenbacker, during a wartime visit to assess the Soviet aircraft industry, when he spoke of the American ‘super-bomber’ then under development. Subsequently, Soviet efforts to acquire B-29s as part of ‘Lend Lease’ were denied by the United States, as were requests for B-17 and B-24 four-engined bombers; the Americans wary of Soviet intentions following the war’s end. Aircraft designer Andrey Tupolev was working on his own four-engined heavy project, ‘Aircraft 64’, which might have been the Soviet Union’s next big bomber if it were not for events raging outside the Soviet homeland.
The timely forced landing in Russia of B-29s engaged on raids against Japan in 1944 and 1945 meant that the Soviets finally had examples of the technologically advanced US aeroplane. Ironically considering the outcome, the Americans were not overly concerned with the fate of these interned machines, believing that three serviceable aeroplanes of five – one of which was returned, were insufficient to be of any real use to the Soviets and that their industry was too primitive to reverse engineer the type. Soviet Premier Josef Stalin had other ideas, however. Anger at the qualitative disparity between the Soviet air force’s (Voyenno Vozdooshnyye Seeley – VVS) bombers and those of their US and British equivalents led him to order the copying of the design.
Following on from the instruction not to continue with Aircraft 64 in favour of building the B-29, Tupolev design bureau OKB-156 was tasked with dissecting the B-29 and producing the new bomber, designated B-4 (for Bombardirovschchik No.4). Under State Defence Committee Directive No.8934 and People’s Commissariat of Aircraft Industry Order No.263, construction of the B-4 took place at Kazan Plant No.22. Tupolev gave the initial time span for duplication of the B-29 and its complex systems as three years; Stalin’s response was succinct; “you have two years”.
Despite the elongated engine nacelles, the graceful lines of the B-29 are clearly evident in this surviving PLAAF Tu-4, on display at the China Aviation Museum at Xiaotingshan, Beijing. The Tu-4 is primarily constructed of duralumin aluminium alloy, with skin thicknesses of between .03 to .07 inches (.8 to 1.8mm), increasing to .078 inches (2mm) at high stressed areas. The fuselage is of streamlined cylindrical shape and circular cross section, constructed in 61 frames supported by longitudinal stringers and transverse pressure bulkheads separating each major sub-section. There are six sub-sections in total, comprising the forward flight deck glazing (Section F-1, Frame 1), the forward cabin, incorprating the flight deck and nose undercarriage bays (Section F-2, Frames 2 to 13), the centre fuselage, incorporating the unpressurised payload bays and wing carry-through box (Section F-3, Frames 13 to 37), the centre pressure cabin, incorporating operational crew positions as well as crew rest area (Section F-4, Frames 37 to 46), the unpressurised after fuselage, incorporating the horizontal stabiliser carry-through box and vertical stabiliser pick-up points (Section F-5, Frames 46 to 57) and the pressurised rear fuselage containing the tail turret and operator station (Section F-6, Frames 57 to 61). Cabin pressurisation was achieved by bleed air from the inboard engines' superchargers, pressure differential depending on altitude being managed by a RDK-47 (Regoolyator Davleniya v Kabinakh) pressure regulator. A pressurised tunnel connected Sections F-2 and F-4, fitted above the wing carry-through box in Section F-3. Each section was assembled separately and joined by flanged sections at each edge, at the final assembly plant. The crew were protected by steel armour plating and bullet proof glass - the pilots had forward facing triplex armoured Plexiglas, armoured seat backs and hinged rear panels, the centre fuselage had an armoured door and casing surrounding the weapons control system processors and the tail gunner had a steel plate and armoured Plexiglas panels.
Of the aeroplanes interned in Russia, it was B-29-15-BW 42-6365 ‘General H.H. Arnold Special’ of the 794th Bombing Squadron/468th Bomb Group (Heavy) that served as the engineering model for the B-4, while B-29-5-BW 42-6256 ‘Ramp Tramp’ of the 770th Bombing Squadron/462nd Bomb Group (Heavy) was used to assess the type’s flying characteristics and provide accurate performance information.
As many as 900 companies were tasked with examination of the various components that make up the B-29, with 105,000 drawings completed within a year. This was a massive undertaking for the industry and many of the techniques used in the B-29’s construction were new and unheard of. The most difficult tasks were the replication of the various non-metallic components, such as high-quality rubber, plastics and synthetic fabrics. These new materials and manufacturing disciplines learned for the B-4’s construction had enormous repercussions for Soviet aviation’s future.
Whilst the majority of the B-29 was reverse engineered, the decision was made from the outset to incorporate existing home-made technology where necessary, such as the new bomber’s engines, defensive armament and certain avionic items, such as radios and Identification Friend or Foe (IFF) equipment. Although the B-29’s Wright R-3350-23A Cyclones were not copied, the 2,400hp Shvetsov ASh-73 18-cylinder radial being substituted, the Wright’s supercharger, starter generator and heat resistant bearings were; the resulting Soviet TK-19 turbo-supercharger was fitted to the ASh-73TK (TK for ‘Torbokompressor’). B-29 42-6256 ‘Ramp Tramp’ served as the engine test bed, having an ASh-73TK installed in the starboard inboard engine nacelle.
The forward fuselage of PLAAF Tu-4 s/n 2806501. Note the three 'Odd Rod' IFF aerials below the nose glazing. The Tu-4 had a nominal crew of 11; six contained within the forward section illustrated here. The aircraft's captain, who was the primary pilot seated to the left, to the captain's right was the co-pilot, with the bombardier ahead of the pilot's position, flight engineer aft of the co-pilot facing rearwards, navigator and radio operator both facing forwards to the right and left respectively. Since Stalin insisted the B-29 was to be closely copied, the pilot's steering wheels had the Boeing logo replicated at their centre! Within the centre fuselage there were four crewmembers; three gunners, who manned the remote gunnery positions under perspex domes on either side and one in the top centre of the compartment and a radar operator manned a station aft of the gunners' positions. In the rear compartment, the tail gunner sat, isolated from the rest of the aircraft.
Structurally, unlike the B-29, built using imperial measurements, the B-4 was entirely transcribed into metric sizes. Alloy thicknesses were deliberately increased over the American originals owing to Soviet design requirements expecting greater strength, which, on completion remarkably resulted in only a one percent increase in weight in the Tu-4 over the American original.
Ten months after receiving manufacturer’s drawings, at Plant 22 on 28 February 1947 the first B-4, s/n 220001 was rolled out; within Stalin’s prescribed ‘two years’. Making its first flight on 19 May, test pilot Nikolai S. Rybko captained 22001 on its first flight, with A.G. Vasil’chenko as co-pilot and V.N. Saginov as flight engineer. Over the next year came examination of the inevitable issues that arose during trials of an entirely new aeroplane, which were carried out by the first 20 production airframes. Despite the various problems, such as malfunctioning radar and electrical systems, constant speed propellers and remotely aimed guns, pilots had a high opinion of the aeroplane, praising its satisfactory performance and handling and its never-before experienced levels of crew comfort in a Soviet combat aircraft.
Much to the surprise of assembled dignitaries, at the August 1947 Tushino Air Display the first three B-4s completed took part in the massed fly past. This caused Western observers to claim that these were the three B-29s that had been retained from the war, since many found it hard to believe that the industry could reverse engineer the highly complex American bomber. The new machine was given NATO’s Air Standards Co-ordinating Committee’s code name of ‘Bull’. Unfortunately, within the first examples of the newly designated Tupolev Tu-4 there were a few of serious accidents caused by engine fires and propeller overspeed occurrences that killed crew and wrote off aeroplanes.
PLAAF Tu-4 s/n 2806501's right hand outboard engine nacelle containing a Zhuzhou WJ-6 turboprop driving a four-bladed Baoding J17-G13 constant speed reversible-pitch propeller. Note the scalloped metal heating elements at each blade's root section. The Tu-4 was nominally powered by four Shvetsov ASh-73 18-cylinder radials delivering 2,400hp at 2,600 rpm at nominal power. The engine had two-stage supercharging, with the first stage comprising two TK-19 (Torbo-Kompressor) exhaust driven turbochargers operating in parallel and controlled electronically through a mechanical governor and could be selected on or off from the cockpit. The second stage in the supercharging process, via an intercooler, comprised a PTsN single-speed engine driven centrifugal blower. Each engine drove a V3-A3 or V3B-A5 16ft 7in (5.06m) diameter four bladed constant speed propeller. Constant rpm was maintained by a R-18V or R-18A (Regoolyator) governor. Engine starting was via an electrically actuated inertia starter, Unit 263. Each engine was mounted to the wing by a welded steel framework fitted to the firewall in six places, with the engine attached to the mount in nine places via vibration dampers. There were electrically driven segmented cowl flaps around the circumference of each nacelle. Chinese Tu-4s were modified by the fitting of turboprops, licence built 4,250 shp Ivchenko AI-20Ms, which were fitted to the Antonov An-12 tactical transport, built under licence as the Shaanxi Y-8.
With performance and handling trials underway, and the first production Tu-4s rolling off the line at Kazan, a second line was established in Plant No.18 at Kuibyshev, which completed its first Tu-4 in February 1949 and a third line in Plant No.23 at Moscow-Fili; its first Tu-4 was completed in early 1950. By late-1948 however, State acceptance trials had been concluded and the new bomber was ready for service entry, but for an administration hiccup. The final report had not been signed, which meant that VVS refused to accept the finished Tu-4s awaiting delivery at the production airfields. In an unprecedented act, and for the only time, Stalin himself signed the final report and from early 1949 the first Tu-4s began equipping bomber squadrons.
The honour of the first VVS unit to receive the Tu-4 goes to the 13th Dahl’ne bombardirovochnaya Aviadiveeziya (DBAD, Long range Bomber Division), with the 185th Gvardeyski Dahl’nebombardiro’vochnyy Aviapolk – GvDBAP, Guards Long Range Bomber Regiment at Poltava. Familiarisation training began for the unit’s crews at Kazan in 1946, peculiarly on a small number of B-17s and B-24s captured during the war and repaired for service use. Typical tactics employed by the regiments involved sending formations of Tu-4s flying towards the far western borders of the Eastern Bloc to test the defences of the countries they would be called on to attack in time of war. With the capacity to carry up to 8 tons of bombs in its two bomb bays, in VVS service the Tu-4 was armed primarily with conventional weapons, although a very small number were modified to carry nuclear bombs.
A variant designated Tu-4A (for Ahtomnyy), was the Soviet Union’s first nuclear bomber. A year before the first detonation of a Soviet nuclear device on 29 August 1949 (Pervaya Molniya – ‘First Lightning’), Tu-4s were involved in ballistics trials in preparation for dropping the real thing. The first live air-drop of a Soviet nuclear device took place from a Tu-4 on 18 October 1951; a 41.2 kiloton RDS-3 was dropped at the Totskoye range from an altitude of 10,000 metres, detonating at 400 m above ground level.
Right hand outer wing of PLAAF Tu-4 s/n 2806501, showing metal skinned aileron at its trailing edge. Originally, the Tu-4 was built with fabric skinned control surfaces. The Tu-4's wings were of twin spar construction with aluminium covering, featuring 32 wing ribs and 24 spanwise stringers and were fabricated in three sections, the centre section passing through the unpressurised centre fuselage and two outer wings fitted outboard of the outer engine nacelles. The wings had an aspect ratio of 11.5 and had an aerofoil similar to RAF.34. The centre section was joined as two halves along the fuselage centreline inside the fuselage section F-3 and was built around two spars. Skin thicknesses varied between .039 to .098 inches (1 to 2.5mm) underneath and between .157 and .196 inches (4 to 5mm) on the top surface. The centre section contained fuel tanks, the four engine nacelles, with each inboard nacelle containing the main undercarriage units, and each single-piece flap. Each outer wing was built as a two-spar unit, with detachable leading edge and tip and was fitted with an aileron at its trailing edge incorporating a servo tab, joining to the wing centre section at Ribs 14L and 14R. Each flap was a single piece spanning the entire length of the wing centre section, making up 19% of the total wing area; maximum deflection was 45 degrees. At the inboard nacelle, each flap incorporated an aft streamlined cone fairing continuing the line of the nacelle. The flaps extended rearwards, then downwards during deflection, electrically actuated by worm drive. Each aileron was of single-spar construction incorporating a false spar, with 32 ribs and covered in fabric. Their leading edges were metal, as was the trim tab. Chinese Tu-4s were modified with metal covered control surfaces.
In service, tactics dramatically changed with the introduction of the new bomber owing to its advanced technology; air crews initially struggled to accommodate the reliance on electronics aiding their tasks, but soon realised that the Tu-4 and its sophistication improved their efficiency considerably. This required much extra training for both air and ground crew, with maintenance on the new type initially far more complex than anything engineers had had to face in the past.
During sorties, bombs were dropped singly, or in series of one, two or four bombs, or in a salvo, with the assistance of the ESBR-45 electric release mechanism. The bomber’s OPB-48 automatic bomb sight enabled precise delivery of war load at any speed and altitude and in cases of poor visibility, the Kobal’t ground mapping radar gave sight to a previously blind aircraft. This equipment was based on the American AN/APQ-13 fitted to B-29s, which in turn was derived on the British H²S radar employed by RAF Bomber Command.
Tu-4 s/n 2806501's six undercarriage wheels are all visible in this image. Note how the flap incorporates the inboard nacelle's after streamlined cone. The Tu-4 was fitted with electrically actuated tricycle undercarriage, with each unit fitted with two wheels; the mains retracting forward into each inboard nacelle and the nose retracting rearward into a bay beneath the flight deck in Section F-2. Each unit was actuated by electrically powered screw jacks, with auxiliary actuators for emergency retraction and extension. Each leg had hydro-pneumatic oleo suspension. Dimensionally, the main wheels were 57.08 by 20.47 inches (1,450 by 520mm) and the nose wheels were 37.4 by 13.77 inches (950 by 350mm). Braking was via a hydraulic drum unit in each main wheel hub. The nose gear was steerable and incorporated a shimmy damper. All undercarriage bay doors remained open whilst the aeroplane was on the ground, and completely enclosing the undercarriage bays with gear retraction.
At Tu-4 bases, radio navigation aids were installed to assist the aircraft during all-weather operations; the bombers were fitted with OSP-48 Instrument Landing System (ILS), this was replaced with SP-50 Materik ILS in later aircraft deliveries, which considerably reduced their operational poor visibility minima. Litiy radio altimeters also aided in all-weather operations.
Remotely operated defensive armament also called for revised practices; from the centre fuselage and tail gunner’s position, four gunners operating the PS-84 remote sighting system could bring fire to bear in almost every direction. The aircraft’s four twin 23mm Nudel’man-Rikhter NR-23 cannon armed turrets and twin tail installation giving almost complete defensive coverage. For crews, comfort levels previously unheard of were experienced in a fully pressurised ‘shirt sleeve’ environment, with such luxuries as rest bunks and hot food, and drinks kept warm in thermos flasks.
In February 1955, the Aviahtsiya voyenno-morskovo flota (AVMF – Naval Air Arm) received its first Tu-4s, as the VVS was about to begin equipping with the jet powered Tu-16. Despite its high performance and long range, the AVMF saw little use for what was considered an obsolescent airframe owing to the introduction of jet bombers, although a number of cruise missile carrying Tu-4KS’ equipped the AVMF air regiments. Under the Kometa (Comet) weapon system comprising Tu-4, cruise missiles and the Kometa guidance equipment, the enormous KS-1 anti-ship missile, which was the same size and configuration as a MiG-15 jet fighter, was carried under each wing.
Underside view of some of the aerials fitted to PLAAF Tu-4 s/n 2806501 modified as an airborne early warning platform, designated KJ-1. The blue dome was retractable and was standard on production Tu-4s and contained the Kobal’t or Kobal't-M (Cobalt) ground mapping radar. The Tu-4 was fitted with a wide range of electronic systems new to the Soviets, as well as conventional communications equipment. Navigation equipment fitted was ARK-4 or -5 automatic direction finders, RV-2 Kristahl short range radio altimeter and RV-10 long range radio altimeter, MRP-45 marker beacon receiver, which was replaced by MRP-48 Dyatel (Woodpecker) in later aircraft. SP-50 Materik (Continent) instrument landing system was fitted in later production machines, comprising SD-1 Shipovnik (Dog rose) distance measuring equipment, KRP-F localiser receiver and GRP-2 glideslope beacon receiver. Comms radios were VHF 1RSB-70, American HF SCR-274N, replaced by Soviet RSB-5, 12RSU-10 VHF command radio replaced by RSU-5 and RSIU-3 in later aircraft, and AVRA-45 emergency radio. Each aircraft was fitted with SPU-14 intercom. Tu-4s were fitted with Magniy (Magnesium) IFF interrogator, replaced with Magniy-M in later aircraft, and SRO-1 Bariy-M (Barium) IFF transponder. The sole Chinese prototype KJ-1 was fitted with a Type 843 rotodome above the centre fuselage as well as a number of radomes and dielectric panels along its underside. Although the rotodome radar was never fitted, it is not known what the various radomes were for or whether they were ever active or not.
The Tu-4 saw only one foreign operator, the Chinese People’s Liberation Army Air Force (PLAAF), which received 25 examples free of charge in the early 1950s. Originally, it was intended that China would employ its Tu-4s as nuclear bombers against the Kuomintang (KMT) on the island of Taiwan, where Chiang Kai-Shek and his followers had fled from the mainland. Souring relations between China and the Soviet Union around this time meant that China did not receive Soviet nuclear bombs. Long range conventional bombing raids were flown from the Chinese mainland against KMT positions on Taiwan, however. During these missions, the Tu-4s were commanded by Soviet pilots, who received considerable reward from the Chinese.
A lack of an immediate successor meant Chinese Tu-4s remained in service far longer than intended, which, because of a lack of engines and equipment support saw indigenous solutions adopted. These included re-engining the bombers with Zhuzhou WJ-6 turboprops – licence copies of the 4,250 shp Ivchenko AI-20M, which was installed in the Shaanxi Y-8, the Antonov An-12BK tactical transport built in China.
Of note was the conversion of a PLAAF Tu-4 into a drone carrier; aircraft s/n 225008 was modified to transport two WZ-5 Chang Hong-1 drones, one under each outer wing, which were a copy of the US Ryan BQM-34A Firebee reconnaissance platform. Another project of note was an airborne early warning aeroplane, for which one was converted. Tu-4 s/n 2806501 was designated KJ-1 and was fitted with a Type 843 rotodome mounted amidships, although workable radar was never installed. The PLAAF considered the KJ-1 as a failure as the entire installation was too heavy and it did not meet the PLAAF’s needs. The last PLAAF Tu-4s were retired from service in the early 1990s.
Fuselage centre section, Section F-4 of PLAAF Tu-4 s/n 225008 showing remote weapon arming blisters, but without gun armament, note the circular blank aft of the top Perspex bubble. The Tu-4’s defensive armament comprised five turrets, four 360-degree traversing units and a single tail turret, consisting of initially the PV-20 system with two 20mm Berezin B-20E cannon in each turret and three in the tail. Production standardised on the PV-23 system with two 23mm Nudelman/Rikhter NR-23 cannon in each station, the tail turret being a DK-3 unit. Total ammunition complement was 3,150 rounds contained within each turret, or in the rear fuselage for the tail guns, which was fed electrically to each gun. Rate of fire was 800 to 950 rounds per minute. Each turret was remotely controlled and operated electrically from five different sighting stations; one in the forward section through the nose glazing, three in the centre fuselage through three independent sighting stations and from the rear gunner’s station, each fitted with a PS-84 remote sighting system. In the forward compartment, the bombardier operated the sighting system, whereas personnel were provided for the other four. The system was highly complex and processed information received from each sighting system electronically, compensating for parallax error of the remote gunners being off-set from the guns’ line of sight.
In Soviet service the Tu-4 also saw combat operations, but not as a bomber; this might have been different if it weren’t for last minute intervention, however. With tensions rising over Hungary’s anti-communist movement in October 1956, VVS Tu-4D troop transports were deployed west for attacks against insurgents. Operating from Chop near the Soviet-Romanian border, these aircraft delivered paratroopers into Hungary and were often fired upon by rebels, but little damage was done to the aeroplanes. On the evening of 4 November, several bomb-laden Tu-4s took off from Borispyl Airport, Kiev bound for Budapest to destroy rebel resistance in the city, but were recalled from this potential disaster whilst overflying Romania.
Aside from its intended role, the Tu-4’s high performance lent it to experimental tasks, which included trialling in-flight refuelling and the novel Boorlaki programme, which saw single-seat fighters towed behind bombers fitted with special towing rigs. This idea was discontinued, as pilots experienced severe discomfort from long hours crammed in the cockpit of an unpowered jet fighter. Tu-4s also made ideal engine test beds; engines trial flown on Tu-4LL test beds included the Invchenko Al-20 and Kuznetsov NK-4 turboprops – both engines fitted to the one airframe; the former for the An-12 and the latter in an over wing installation as on the Il-18 airliner. The Mikulin AM-3 turbojet was also trialled in a pod under a Tu-4LL’s fuselage.
Exact numbers of Tu-4s built is not confirmed, with varying sources quoting different figures. Russian historians claim around 900, with the VVS operating 847, but figures released from the manufacturing plants offer between 1,100 and 1,200. Only three complete airframes survive, the Chang Hong-1 drone carrier and KJ-1 at the China Aviation Museum at Xiaotingshan, near Beijing and a single Kuibyshev built aeroplane, s/n 2805103 at the Central Air Force Museum at Monino, Moscow.
PLAAF Tu-4 s/n 225008’s tail feathers, with prominent endplate fins added to its horizontal stabilisers. These were added to offset the extra keel area of carrying an underwing payload, in this aircraft’s case two WZ-5 Chang Hong-1 drones, copies of the US Ryan BQM-34A Firebee. The Tu-4’s empennage comprised conventional vertical and horizontal stabilisers of metal construction, with fabric covered control surfaces, although Chinese Tu-4s were later modified with metal skinned surfaces. The vertical tail employed a symmetrical aerofoil section, being of two spar construction, with a false forward spar and incorporated 23 ribs for shaping. Its skin thickness was .023 inches (0.6mm). Attached to the lower forward section was a fin fillet that had a false spar and 24 frames that provided shape, gently curving from the exterior line of the fin. The rudder had a single spar and a rear false spar for the fitting of a metal trim tab at its lower trailing edge, and comprised 16 ribs aligned vertically. Its leading edge was metal, whilst its exterior was fabric covered. The tailplane attached to the unpressurised after fuselage, Section F-5 at Frame 53. It featured an asymmetrical inverted aerofoil section and zero dihedral. The entire horizontal stabiliser was constructed as a single, twin-spar unit with 27 ribs and 22 stringers supporting the outer skin. Its trailing edge was occupied by the symmetrical elevator, constructed of duralumin, with 20 ribs and a false spar to support a trim tab at its inboard trailing edge. Like the rudder, its leading edge was metal and its exterior was fabric covered. Within the tail section a ventral gun turret and vertical camera was housed, as well as ammunition boxes for the tail guns. An M-10 auxiliary power unit (APU) was fitted on the port side within this section. The M-10 APU was a 10hp two-stroke motor, which provided power generation through a GS-5000 generator. A hydraulically cushioned tail skid was fitted under the fuselage below the horizontal stabiliser.
Information for this article largely came from the excellent books Tupolev Tu-4 – Soviet Superfortress by Yefim Gordon and Vladimir Rigmant (2002, Midland Publishing, Hinkley), The Osprey Encyclopedia of Russian Aircraft 1875 – 1995 by Bill Gunston (1995, Osprey Aerospace, London) and Chinese Aircraft; China’s Aviation Industry since 1951 by Yefim Gordon and Dmitry Kommissarov (2008, Hikoki, Manchester).
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