Sukhoi T-4 Sokta

As with most significant military developments during the Cold War, the XB-70A was Matched by a Soviet counterpart. In this case it was the Sukhoi T-4 (also called Project 100). This titanium and stainless steel aircraft was powered by four 35,274-lbf Kolesov RD36-41 turbojet engines and was designed to reach Mach 3. The development program was cancelled before the aircraft ever flew that fast. Like the B-70, the T-4 had an articulating nose, but in the up position all forward vision was lost.

In 1963, the Soviet government issues a requirement for developing an aircraft analogous to the North American XB-70 Valkyrie. Sukhoi, Tupolev and Yakovlev competed with the T-4, Tu-135 and Yak-33. The Sukhoi design, with its high cruise speed of 3,200 km/h was favored over the other two designs. In 1964, the building of a prototype was authorized. The first T-4, designated “101”, first flew in 1972. Testing continued to 1974. The T-4 flew only ten times for a total 10 hours and 20 minutes. It is believed to have reached at least Mach 1.3 at an altitude of 12,000 meters. Construction on the second T-4 aircraft “102” began in 1969 and completed in 1973. The first flight for 102 was scheduled for the end of 1973. In the end, the Soviet Air Force decided to go with an improved version of the TU-22 Blinder, which became the TU-22M Backfire. It was felt that a modification of the Blinder was easier to do than to build a new T-4 aircraft. The project was abandoned.

This enormous project was triggered in December 1962 by the need to intercept the B-70(or RS-70), ‘A-11’ (A-12, later SR-71), Hound Dog and Blue Steel. At an early stage the mission was changed to strategic reconnaissance and strike for use against major surface targets. It was also suggested that the basic air vehicle could form the starting point for the design of an advanced SST. From the outset there were bitter arguments. Initially these centred on whether the requirement should be met by a Mach-2 aluminium aircraft or whether the design speed should be Mach 3, requiring steel and/or titanium. In January 1963 Mach 3 was selected, together with a design range at high altitude on internal fuel of 6,000km (3,728 miles). General Constructors Sukhoi, Tupolev and Yakovlev competed, with the T-4, Tu-135 and Yak-33 respectively.

The Yak was too small (in the TSR. 2 class) and did not meet the requirements, and though it looked like the B-70 the Tupolev was an aluminium aircraft designed for Mach 2.35. From the start Sukhoi had gone for Mach 3, and its uncompromising design resulted in its being chosen in April 1963. This was despite the implacable opposition not only of Tupolev but also of Sukhoi’s own deputy Yevgenii Ivanov and many of the OKB’s department heads, who all thought this demanding project an unwarranted departure from tactical fighters. Over the next 18 months their opposition thwarted a plan for the former Lavochkin OKB and factory to assist the T-4, and in its place the Boorevestnik (stormy petrel) OKB and the TMZ factory were appointed as Sukhoi branch offices, the Tushino plant handling all prototype construction. A special WS commission studied the project from 23rd May to 3rd June 1963, and a further commission studied the refined design in February-May 1964. By this time the T-4 was the biggest tunnel-test project at CAHI (TsAGI) and by far the largest at the Central Institute of Aviation Motors. The design was studied by GKAT (State aircraft technical committee) from June 1964, and approved by it in October of that year. By this time it had outgrown its four Tumanskii R-15BF-300 or Zubets RD-17-15 engines and was based on four Kolesov RD-36-41 engines. In January 1965 it was decided to install these all close together as in the B-70, instead of in two pairs. Mockup review took place from 17th January to 2nd February 1966, with various detachable weapons and avionics pods being offered. Preliminary design was completed in June 1966, and because its take-off weight was expected to be 100 tonnes the Factory designation 100 was chosen, with nickname Sotka (one hundred). The first flight article was designated 101, and the static-test specimen 100S. The planned programme then included the 102 (with a modified structure with more composites and no brittle alloys) for testing the nav/attack system, the 103 and 104 for live bomb and missile tests and determination of the range, the 105 for avionics integration and the 106 for clearance of the whole strike/reconnaissance system. On 30th December 1971 the first article, Black 101, was transferred from Tushino to the LII Zhukovskii test airfield. On 20th April 1972 it was accepted by the flight-test crew, Vladimir Ilyushin and navigator Nikolai Alfyorov, and made its first flight on 22nd August 1972. The gear was left extended on Flights 1 through 5, after which speed was gradually built up to Mach 1.28 on Flight 9 on 8th August 1973. There were no serious problems, though the aft fuselage tank needed a steel heat shield and there were minor difficulties with the hydraulics. The WS request for 1970-75 included 250 T-4 bombers, for which tooling was being put in place at the world’s largest aircraft factory, at Kazan. After much further argument, during which Minister PV Dement’yev told Marshal Grechko he could have his enormous MiG-23 order only if the T-4 was abandoned, the programme was cancelled. Black 101 flew once more, on 22nd January 1974, to log a total of 10hrs 20min. Most of the second aircraft, article 102, which had been about to fly, went to the Moscow Aviation Institute, and Nos 103-106 were scrapped. Back in 1967 the Sukhoi OKB had begun working on a totally redesigned and significantly more advanced successor, the T-4MS, or 200. Termination of the T-4 resulted in this even more remarkable project also being abandoned. In 1982 Aircraft 101 went to the Monino museum. The Kazan plant instead produced the Tu-22M and Tu-160.

In all essentials the T-4 was a clone on a smaller scale of the North American B-70. The structure was made of high-strength titanium alloys VT-20, VT-21L and VT-22, stainless steels VIS-2 and VIS-5, structural steel VKS-210 and, for fuel and hydraulic piping, soldered VNS-2 steel. The wing, with 0° anhedral, had an inboard leading-edge angle of 75° 44′, changed over most of the span to 60° 17′. Thickness/chord ratio was a remarkable 2.7 per cent. The leading edge was fixed. The flight controls were driven by irreversible power units in a quadruplex FBW (fly-bywire) system with full authority but automatic manual reversion following failure of any two channels. They comprised four elevens on each wing, flapped canard foreplanes and a two-part rudder. The fuselage had a circular diameter of 2.0m (6ft 6%in). At airspeeds below 700km/h (435mph) the nose could be drooped 12° 12′ by a screwjack driven by hydraulic motors to give the pilot a view ahead.

Behind the pilot (Ilyushin succeeded in getting the proposed control wheel replaced by a stick) was the navigator and systems manager. Both crew had a K-36 ejection-seat, fired up through the normal entrance hatch, and aircraft 101 also had a pilot periscope. Behind the pressure cabin was a large refrigerated fuselage section devoted to electronics. Next came the three fuel tanks, filled with 57 tonnes (125,661 Ib) of specially developed RG-1 naphthyl fuel similar to JP-7. Each tank had a hydraulically driven turbopump, and the fuel system was largely automated. A production T-4 would have had provision for a large drop tank under each wing, and for air refuelling. Behind the aft tank were systems compartments, ending with a rectangular tube housing quadruple cruciform braking parachutes. Under the wing was the enormous box housing the air-inlet systems and the four single-shaft RD-36-41 turbojets, each with an afterburning rating of 16,000kg (35,273 Ib). An automatic FBW system governed the engines and their three-section variable nozzles and variable-geometry inlets. Each main landing gear had four twin-tyred wheels and retracted forwards, rotating 90° to lie on its side outboard of the engine duct. The nose gear had levered suspension to two similar tyres, with wheel brakes, and used the hydraulic steering as a shimmy damper. It retracted backwards into a bay between the engine ducts. The four autonomous hydraulic systems were filled with KhS-1 (similar to Oronite 70) and operated at the exceptional pressure of 280kg/cm2 (3,980lb/in2). A liquid oxygen system was provided, together with high-capacity environmental systems which rejected heat to both air and fuel. The crew wore pressure suits. The main electrical system was generated as 400-Hz three-phase at 220/115 V by four oil-cooled alternators rated at 60 kVA. Aircraft 101 never received its full astro-inertial navigation system, nor its planned ‘complex’ of electronic-warfare, reconnaissance and weapon systems. The latter would have included two Kh-45 cruise missiles, developed by the Sukhoi OKB, with a range of 1,500km (932 miles).

Like the B-70 this was a gigantic programme which broke much new ground (the OKB said ‘200inventions, or 600 if you include manufacturing processes’) yet which was finally judged to have been not worth the cost.

Sukhoi T-4MS

In 1967, the USAF launched a program of the B-1 Lancer supersonic-strategic bomber which has a blended wing body configuration, with variable-sweep wing and four turbofan engines. The USSR prompted to maintain the strategic balance. A requirement for the research and development of a new bomber was issued to three design bureaus which resulted as Myasishchev M-18, Sukhoi T-4MS and Tupolev 160. The Sukhoi T-4MS was based on an earlier T-4 Sotka supersonic bomber. It was codenamed “S-200” as it’s take off weight approached 200 tons. In 1972, the three designs were presented to the Ministry of Aviation Industry. The T-4MS was chosen as the winner of the competition. However, the USSR Air Force felt that Sukhoi would be unable to handle the T-4MS development as the bureau was already involved many new fighters projects. Sukhoi was ordered to stop the development and transfer all the research works of the T-4MS to Tupolev bureau. Tupolev declined the offer and continued the “Article160” design with variable geometry wing which became the Tu-160 Blackjack bomber. 

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