Earlier experience with the T-58VD design, manufacturing and flight testing gave the design bureau the capability to design a STOL aircraft, designated T6-1, which became the first new-generation attack aircraft. Conceptual design work began in 1965. For the first time in the history of the Design Bureau, the loft technique was used for structural assembly coordination.
In one of the design rooms was a 49 ft 3 in (15 m) long drawing board, installed vertically and covered with a reference grid, on which a reduced scale aircraft side view was drawn. This drawing included external aircraft lines, air ducts, boundary layer air bleed wedges, additional air intakes and nozzle units, fuel tank contours, engine contours, radio equipment, aircraft system units contours, aircraft and engine control circuits, electrical wiring, hydraulic and pneumatic pipelines, fuel pipelines and ventilation system ducts and some structural members, including the landing gear assemblies in a retracted position. In addition, all of this information was plotted on fuselage cross section lofts in full-scale.
A T6-1 prototype was manufactured by the summer of 1967. It flew for the first time, with Vladimir Ilyushin at the controls, on July 2. It was planned to display the aircraft at the Domodedovo air show. However, the aircraft was not fully developed and it did not fly at Domodedovo.
In 1969, after intensive tests, the R-27F2-300 cruise engines of the T6-1 were replaced by Arkhip Lyulka AL-21 Fs. For this purpose, the rear fuselage was reworked. This involved not only the external contours but also the structure. The air brake panels, which had been placed on the rear fuselage, were removed. As a result of the flight tests, to improve directional stability characteristics, the wing tips were turned down and ventral strakes were installed on the fuselage bottom.
Because of the radar designer’s requirement, the fuselage nose radome dimensions were changed. Initially, the radome dimensions were chosen to meet the required supersonic performance. The radome became shorter and more obtuse. Tests proved the aircraft, with the new radome, to be capable of the required speed.
Sukhoi T6-1A more precise definition of the requirements for the new generation of attack aircraft along with the T-58VD and T6-1 flight test results and the theoretical analysis of twelve different aerodynamic shapes resulted in the Chief Designer abandoning the hybrid powerplant. Thus began the design of a variable-geometry attack aircraft. Further tests of aircraft with lift engines were stopped and the T6-1 was used as a test bed for radio equipment. From 1967 until 1970, the aircraft flew approximately 120 test flights. From 1971 until 1974, it was used more efficiently and flew more than 200 flights. In 1974 its service career was over. Today, the composite powerplant T6-1 prototype is an exhibit at the aircraft museum in Monino.