Su-24 FENCER (SUKHOI) - T6-2I Variable Sweep Wings
Starting mid-1967, the Design Bureau began to look into the option of engineering the T-6 with variable sweep wings. The characteristic that most readily identifies the type, performance and purpose of an airplane is the shape of its wings. There are four basic wing types: straight wings, sweep wings (forward-sweep/sweepback), delta wings and the swing-wing (or variable sweep wing). Each shape allows for premium performance at different altitudes and at different speeds.
For an airplane which is designed to be multimission, for example, subsonic cruise and supersonic cruise, it would be advantageous to combine a straight wing and swept wing design. This is the logic for the variable sweep or swing-wing. Although not necessarily equal to the optimum configurations in their respective speed regimes, it was evident that an airplane with a swing-wing capability can in a multimissioned role, over the total speed regime, be better than the other airplanes individually. One major drawback of the swing-wing airplane is the added weight and complexity of the sweep mechanisms. Like a number of other aviation designers, Sukhoi embraced the concept of evolutionary development rather than large technological leaps in aircraft design. For example, Sukhoi improved the original Su-9 delta-winged series into the Su-11 and Su-15 fighter-interceptor series for service with the Soviet Air Defense Forces. He also modified the Su-7B ground-attack aircraft into the Su-17 variable-geometry aircraft by introducing small modifications to the original design. Sukhoi's aircraft symbolized the general trend of Soviet aircraft design that used common components and standardization that allowed Soviet plants to produce large numbers of aircraft very quickly. The Su-22 Fitter, variable-geometry, ground-attack aircraft was first seen as a prototype in Moscow in 1967 and was exported to Poland and Czechoslovakia for fielding with their air forces. The Su-22 can fly at speeds up to 2,200 kilometers per hour and had a combat radius of 250 to 345 kilometers. Officially, the efforts to develop the new plane got underway following a decree of the government of 7th August 1968, with the PR for the aeroplane finalised by the Air Forces as an addendum to the 1965 requirements. The T-6 detailed design revision was completed in 1968-69, with two prototypes built by the autumn of 1969. The first flying prototype of the T6-2I airplane was moved to the Design Bureau's flight test and development base (FT&DB) at FRI on 10th November 1969. The first flight was performed by V.S. Ilyushin on 17th January 1970. The T-6 official tests took as long as four years: from January 1970 to July 1974. Such a long test period was due to the great complexity and newness of the tasks facing the Design Bureau and the military in the course of refining the aircraft. The T-6 became the USSR's first attack airplane of the tactical air arm to be deployed day or night in all weather. This was achieved thanks to the Puma ANS consisting of two Orion-A superimposed radar scanners for nav/attack and a dedicated Relyef terrain clearance radar to provide automatic control of flights at low and extremely low altitudes. The ANS incorporated an Orbita-10-58 onboard computer, the armaments including Kh-23 and Kh-28 type air-to-ground guided missiles, together with R-55 type air-to-air guided missiles. A distinctive feature of the T-6 design was the use of a variable geometry shoulder wing, which gave the aeroplane acceptable takeoff and landing characteristics (TOLC) and superior APC in various flight modes. Another major design feature of the aeroplane was the extensive use of long-length machined panels. For the first time in two-seat planes of this class the Soviet aviation industry saw a side-by-side crew accommodation arrangement and a standardized type of K-36D ejection seat, allowing the pilots to bail out at any altitude and flight speed, including during takeoff and landing. By the 1980s, however, no one was designing variable-sweep aircraft and no new work on this technology has been incorporated into any new production military aircraft in at least the last 15 years, although work is still being carried out on wings that move in other ways. The technology of variable-sweep wings lasted little more than 20 years before being phased out, although hundreds of the aircraft continued to fly for years more. There were several reasons for the move away from this technology, but the primary reason was that the large metal gearbox needed to move the wings was complicated and heavy. This increased maintenance requirements and decreased fuel performance. An aircraft capable of moving its wing forward for fuel-efficient flight could never be as efficient as an airplane equipped with a straight wing. The same was true for aircraft with swept-back wings; they would always be more efficient than aircraft with swing-wings.