Supersonic VTOL fighter project
The work on the project of a supersonic VTOL aircraft designated Yakovlev Yak-41 (izdeliye 48) was initiated by the Yakovlev OKB in 1975. It was formally endorsed by a government directive issued in November 1977 which tasked Yakovlev with creating a supersonic VTOL fighter; the latter was to be submitted for State acceptance trials in 1982. The work was conducted initially under the guidance of Sergey A. Yakovlev (the General Designer’s elder son) as project manager.
As is usual at an early project stage, several widely differing aerodynamic configurations and powerplant layouts were considered. Initially preference was given to a layout based on the use of a single lift/cruise engine. Gradually the emphasis shifted to studying alternative layouts based on the use of a powerplant comprising two types of engines a la Yak-38, albeit the work on the single-engine layout continued for a while.
The earliest project version of the Yak-41 was an aircraft featuring a single lift/cruise engine with a single large vectoring nozzle. A model shows it with a fuselage and tail unit similar to those of the Yak-38. but featuring a pointed nose cone (possibly intended to house a radar) and a chin air intake with a movable half-cone centrebody beneath this cone; the moderately swept wings had small leading edge root extensions (LERXes) and a single vectoring engine nozzle was placed under the fuselage right aft of the wings.
Another proposed version made use of an aft-mounted lift/cruise turbofan with a two-dimensional thrust-vectoring nozzle. It used separate outlets for the core and bypass flows, the bypass flow being ducted to a small afterburner chamber in the forward fuselage; it was intended to balance the thrust created by the flat vectoring nozzle. The layout was, however, considered too complicated to be viable.
Yet another, completely different Yak-41 configuration studied in 1979 was based on the Yak-45 twinjet fighter project that earlier had lost out to the Su-27 and MiG-29. In its original form, the Yak-45 had a normal tail unit in combination with composite-sweep (double-delta) wings carrying two engines underneath. The project of the VTOL version inherited the cranked wings of the Yak-45, replacing the normal tail unit with canard foreplanes and adding thrust-vectoring nozzles to the underwing-mounted main engines, which were moved forward to place the nozzles under the wings. The machine would also be fitted with two widely spaced RD-38 lift engines in the centre fuselage. The rather exotic layout was not proceeded with. This list of project variants is by no means exhaustive.
Another series of studies, eventually leading to the final prototype configuration, was based on the use of a composite powerplant, wings with prominent LERXes and a twin-boom tail unit with twin fins and rudders. The latter feature was due to the need to place the vectoring nozzle of the main (lift/cruise) engine closer to the CG so as to shorten its arm and ensure balance with the lesser thrust of the two lift engines placed in the forward fuselage. In one of the studies, the lift engines were placed in the extreme nose, between the cockpit and the radar, in order to widen the distance between these engines and the vectoring nozzle of the main engine. This layout proved unacceptable for a number of reasons. The lift engines had to be placed aft of the cockpit. An interim design study coming close to the final shape differed from it only in having Dassault Mirage-style semi-circular air intakes of the lift/cruise engine; they gave way to the MiG-31-style raked rectangular intakes on another study coming still closer to the future prototype.
In March 1979 the OKB completed the advanced development project and a full-scale mock-up of an aircraft powered by a single lift/cruise engine – a Khachatoorov R79V-300 afterburning turbofan. At the same time the OKB submitted to the Ministry of Defence a proposal for a multi-purpose fighter capable of carrying a wider weapons complement and equipped with a composite powerplant. The latter was to comprise two RD-41 lift engines, each delivering a thrust of 4,100 kg (9,040 lb), and a single R79V-300 lift/cruise engine rated at 15,500 kg (34,180 lb). That was deemed sufficient to enable the aircraft to lift off vertically or with a short take-off run from a carrier deck at an AUW of 19,500 kg (43,000 lb).
Yet, the design could not be ‘frozen’ because of a series of changes successively introduced into the SOR which initially envisaged a fighter aircraft, then, additionally, an attack aircraft based on the latter, and finally, a multi-purpose aircraft which was intended to perform missions ranging from beyond visual range (BVR) intercept and dogfighting to attacks against surface ships and land targets.
Accordingly, the construction of prototypes was repeatedly postponed, not least because of delays in the development of the new engines. It was not before the end of 1984 that the R79V-300 lift/cruise engine was ready for bench testing. The Yakovlev Yak-41 s submission for tests was postponed to 1985, but that proved to be unrealistic, too. Yakovlev’s retirement in 1984 was one of the circumstances impeding the work on the VTOL machine; as a result, the directive of 1977 was to remain unfulfilled.