The Sukhoi Su-37 made a spectacular impact.

Alexander Velovich/MOSCOW

SPECTACULAR EVIDENCE that the Russian aircraft industry is still alive came to the 1996 Farnborough air show with the international debut of Sukhoi's thrust-vectoring Su-37 Flanker. The aircraft is a further development of the Su-27/35 fighter series, and, although it is characterised by its designers as an experimental development prototype, it is much more of a basis for a combat fighter than was the US/German X-31 research aircraft which was used to entertain the public with exotic manoeuvres at the Paris air show in 1995.

The Su-37 has an integral flight-control system, with a sidestick implementing thrust vectoring through control algorithms. Other innovations include wide field-of-view head-up display and liquid-crystal multi-function displays on the instrument panel. Sukhoi acknowledges that French electronic equipment has been installed in the fighter, but refuses to reveal the name of the manufacturer (probably Sextant Avionique), hidden under the acronym "FPI".

Sukhoi began experiments with thrust vectoring in the late 1980s, when Lyulka developed a two-dimensional nozzle for its AL-31 engine, which was tested on one of Sukhoi's Su-27 development prototypes. Although valuable experience was gained, it was decided that axisymmetric configuration of the jet nozzle would be more promising.

Lyulka concentrated on the development, of an engine modification, designated the AL-37F. Another flying testbed, with one of the engines equipped with an axisymmetric nozzle, was tested in the early 1990s. In 1995, two thrust-vectoring engines were installed on a modified version of the Su-27M, with the constructor's number 711. While the modified Flanker received the designation Su-35, it was decided to give the 711 a new model number, the Su-37.

The nozzle of the Al-37F engine has thrust vectoring only in pitch, but Lyulka general designer Victor Chepkin says that the bureau "-has a full [two-axis]-vectoring nozzle in its pocket", although it is unlikely to be used on the Su-37 because its tail boom and twin-engined configuration makes it difficult to vector thrust in yaw. The vectoring mechanism is driven by hydraulic actuators, with a back-up system to return the nozzles to neutral position by compressed air. There are no restrictions on engine thrust, so full afterburner can be engaged while the nozzles are fully deflected. Differential thrust-vectoring is used for bank control at extremely low speed, and that, too, was demonstrated. A similar nozzle design is believed to be implemented on the fifth-generation Lyulka Al-41 powering the Mikoyan 1.44 advanced fighter demonstrator, which is expected to be flown soon.

Besides thrust vectoring, the AL-37F has had its thrust increased to 28kN (6,350lb), from the 25kN of the AL-31F. This has been achieved by raising airflow through the fan to 120kg/s from the current 112kg/s on the AL-31. The dry mass of the new thrust-vectoring engine is 1,600kg, only 70kg heavier than the series production model. Another factor of improvement is the increase in turbine-inlet temperature, from 1,450ûC to 1,530ûC. This is made possible by changing the design of the circular combustion chamber.

The most spectacular thrust-vectoring manoeuvre demonstrated at Farnborough was a backward flip-flop, during which the aircraft was pitched up instantly, fell on its back and was recovered into level flight, continuing half a loop from the inverted position at almost zero airspeed, with an extremely tight turning radius compared with the length of the aircraft.

The Su-37 programme suffers from inadequate financing. The aircraft is also being used to test some of the electronic equipment and design solutions which may be incorporated on board the Sukhoi Su-34 bomber.

Source: Flight International