The basic configuration of Tupolev Tu-244 was a tailless delta with the four engines housed separately, a take-off weight of 320-350 tonnes and a cruising speed of Mach 2.0-2.05. The selected takeoff weight, dimensions and passenger capacity of 250-300 or even more, would enable it to compete with such subsonic aircraft as the Boeing 747 and the Airbus Industrie A310 which carried between 300 and 500 passengers. The layout of the Tu-244 was designed to provide a high lift/drag ratio in supersonic cruise (up to 9 and above) and subsonic speeds (up to 15-16) and for take-off and landing, together with noise reduction and enhanced passenger comfort.
The cranked-delta wing with large leading edge extensions has complex camber on its central section and the wing airfoil varies across the span. Pitch and roll control and trim are provided by elevons, and leading-edge flaps are provided for greater lift. Compared to the Tupolev Tu-144, the basic wing section has significantly less leading-edge sweep while retaining sharply swept-back leading edge root extensions to reach a compromise between the behaviour at high supersonic cruising and subsonic speeds. The wing structure is similar to the Tu-144’s, and provision has been made for the extensive use of composite materials in the structure of the wings, fuselage, tail assembly and engine housings to achieve a saving of 25-30% in airframe weight.
As on the Tupolev Tu-144, the vertical tail has a two-section rudder and is of similar construction to the wings. The fuselage comprises the pressurised cabin with nose and tail sections. The optimum fuselage crosssection to accommodate 250-320 passengers appears to be 3.9 m wide and 4.1 m high. The Tu-244 has no drooping visor nose, as the cockpit glazing is adequate for flying and the necessary field of view for take-off and landing is provided by optoelectronic systems. The increase in take-off weight has necessitated alterations in the undercarriage and, unlike the Tu-144, this comprises a single nose gear unit and three main units, of which the two outer ones have three-axle 12-wheel bogies retracting into the wings, while the twin-wheel centre unit retracts into the fuselage. The take-off thrust of each engine is be around 25,000 kgp, although the exact type is not yet clear; variable-cycle engines and conventional turbofans with ejector nozzles to suppress noise on take-off and landing are being considered. Systems and equipment will take the experience gained with the Tu-160 and Tu-204 into account.
In an effort to take a flexible approach to the problems of the SST-2, several possible variants of the Tu-244 differing in weight, dimensions, passenger capacity and small details of layout were prepared. One of the latest Tu-244 variants proposed by the OKB has a take-off weight of 300 tonnes, a wing area of 965 m2, four turbojets providing around 25,500 kgp for take-off and carries 254 passengers. Its estimated operating range at supersonic speed with a normal payload is 7,500 km.
The Tu-144LL ‘Moskva’ (Moscow) research aircraft based on a production Tu-144D has been a valuable contribution by Russia to the development of an SST-2. Work on the Tu-144LL has come under the umbrella of Russian-US co-operation with active financial support provided by the Americans. Production Tu-144D RA-77114 was selected for conversion, its RD36-51A turbojets being replaced by NK-321 turbofans (a modification of the Tu-160’s NK-32) in new engine nacelles with revised air intakes; the wings were reinforced, the fuel system and other systems revised and a monitoring and test equipment suite fitted. The Tu-144LL made its first flight on 29th November 1996.
In the course of twenty-seven flights made under the joint research programme, eight unique experiments were performed to determine pressure distribution, the friction coefficient, boundary layer parameters, temperature distribution along the airframe surface, internal engine temperatures, cabin noise and the acoustic loading on elements of the structure. For the first time the results of the take-off and landing characteristics of low aspect ratio large-area wings flying over the runway at very low level have been recorded. Assessments of the aircraft’s performance including stability and handling have been made by several test crews, and NASA test pilots have participated in three flights.