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Sukhoi T-4
The Sukhoi T-4, or “Project 100”, was a Soviet high-speed reconnaissance, anti-ship and strategic bomber aircraft that did not proceed beyond the prototype stage.
As explained by David Baker in his book Russian Bombers, work on Sukhoi Project 100 (denoting the desired gross weight in tonnes), more commonly known as the T-4, began in September 1961 with the bureau’s Oleg Samoilovich very much in charge of design.
The formal requirement for it had originated in the spring of 1962.
The T-4 was to have a range of up to 6,000km (3,726 miles) and a maximum speed of up to 3,200km/h (1,988mph, Mach 3), pushing the technological boundaries of the early 1960s. Weight and range were driven by the need for rough field operation and for deep strike, respectively; the maximum speed was constrained by the thermal properties of materials, as it had been for other supersonic bomber projects from Myasishchev and Tupolev.
A commission created by the Soviet Air Force was assigned to conduct a detailed analysis of the Sukhoi study from 23 May to 3 June 1963, following which conditional approval was given to proceed to final detailed design and the construction of a prototype. The T-4’s projected performance was considered to be within expectations, powered by two Tumansky R-15BF-300 or two Zubets RD-17-15 turbojets, either of which would be suitable. The Council of Ministers had given their agreement to the project by the end of 1963 and it was expected that flight testing would begin within five years.
Project 100 design
During the period following initial approval, Sukhoi had considered around 130 different configurations, throwing the net wide across all forms of propulsion and conceptual layouts, including nuclear propulsion but it did not stop at the required role. Pavel Sukhoi saw his star in the ascendant and had plans drawn up for a T-4 with variations on the basic design being suitable for long-range interception of incoming threats or even for application as a supersonic airliner. This latter consideration mirrored contemporary Anglo-French efforts which would eventually produce Concorde.
In further analysis of the Project 100 design, another inspection was made by the commission between February and May 1964 with Soviet State Committee on Aviation Technology (GKAT) examining the concept in June that year, receiving approval four months later. Further design changes were introduced, significantly the adoption of four Kolosev RD-36-41 turbojet engines, developed by OKB-36 and manufactured at the Rybinsk Motor Building Plant, instead of the previous options. In January 1965 the T-4’s engines were relocated to the back of the delta wing in much the same arrangement as that on the XB-70A, each producing a thrust of 156,800N (35,275 lb). With these, the aircraft was believed to have a maximum speed of 3,200km/h (1,989mph) at 20,000m (60,617ft) and a top sea- level speed of 1,100km/h (684mph).
The mock-up
But there were still several changes to come for the overall design and layout, some innovative concepts being examined based on reports about the Lockheed SR-71, which had taken the Russians by surprise. Throughout, studies concerning the T-4’s aerodynamics had occupied much wind tunnel time and Central Aerohydrodynamic Institute (TsAGI) focused a lot of resources on the project. Reviews of the mock-up took place in December 1966 and between 17 January and 2 February 1967; final design details were evaluated through the mock-up commission.
At this stage, approval had been granted for a static test article and a single prototype (101) before the second prototype (102), with a reconfigured structural arrangement and with composites replacing alloys, was used for testing the navigation/attack system. Two further prototypes (103 and 104) would conduct weapons tests and range evaluation and avionics would be tested on a fifth prototype (105) before a pre-production demonstrator (106) was built for full evaluation of the entire aircraft and its systems.
The mock-up had cranked-delta wing area of 291m² (3,132ft²) and leading edge sweep of 70 degrees on the inner section with 60 degrees on the outer panels. Wingspan was 22m (72ft) and fuselage length was 43.7m (143.3ft). The wing had a thickness ratio of 2.7% but the maximum take-off weight had grown to 146 tonnes (230,600lb), belying the Project 100″ designation. Nevertheless, it promised a maximum speed of 3,000km/h (1,864mph) and a range of 6,200km (3,853 miles). The T-4 by now enjoyed widespread support, despite Pavel Sukhoi’s tetchy relationship with the Tushino fabrication facility where the giant bomber was to be built.
Kh-45 anti-ship missile
During preparations for the initial hardware fabrication stage, Project 100 expanded to embrace wide range of aircraft adapted for specific test roles, including a Su-9 converted to evaluate handling characteristics with the type of wing the T-4 would have. Over time, other wing planforms were tested on this aircraft to determine their suitability or otherwise. Additional aircraft contributed by the Air Force were used to test and evaluate some control system concepts such as fly-by-wire (FBW), electronic navigation sets and autopilots. Despite never having previously designed a missile, Sukhoi developed the Kh-45 anti-ship missile specifically for the T-4. It weighed 4,500kg (9,922lb), had a range of up to 600km (373 miles), a speed of 7,000km/h (4,350mph) and carried a nuclear warhead. It was eventually cancelled but not before being considered for the Tu-160 Blackjack.
Fabrication of the T-4 began in 1969, with the centre and forward fuselage sections transferred to the Sukhoi assembly shop for installation of equipment and aircraft systems. The first aircraft was moved across to the Sukhoi test facilities in December 1971 while the structural test article (100S) was fabricated at the Tushino factory and taken from there to TsAGI. Of some concern was the drooping nose section which was given special thermal testing to ensure its viability. Prototype 101 arrived at the Zhukovsky flight test facility on 30 December 1971 and was accepted for trials on 20 April 1972.
Support for the Sukhoi T-4 slips away
An extraordinary amount of pre-flight testing and 12 taxi runs prevented the first prototype flight from taking place until 22 August 1972, when it was piloted by Vladimir Ilyushin accompanied by navigator Nikolai Alferov. The initial phase of testing comprised 10 flights. The second prototype was finished in 1973 and expected to fly by the end of the year with the third prototype in 1974 and successive aircraft up through 106 thereafter. The Soviet Air Force had great plans for the T-4 and requested resources for 250, which was unexpected. In its brief period of fight testing the T-4 showed promise, demonstrating a speed of Mach 1.28, and its advanced autopilot and FBW proved successful.
However, the size of the aircraft, the resources required to manufacture it and the infrastructure needed to operate it brought strong criticism. For these and other issues concerning cost and its impact of the overall inventory, support for the Sukhoi T-4 began to slip away and acceptance for a limited production run never came. There were other contenders, less sophisticated, closer to existing production line designs and cheaper. Moreover, Defence Minister Marshal Andrei Grechko wanted money for a new generation of MiG fighters and fighter-bombers and the Sukhoi T-4 threatened to drain the coffers.
Russian Bombers is published by Mortons Books and is available to order here.
Photo credit: Unknown and Mike1979 Russia Own Work / Wikipedia
