Supersonic resurrection

This story is sourced from Flight International
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It seemed as if the Tupolev Tu-144was bound for the scrapheap, but things have now changed.

Paul Duffy/MOSCOW

When Marshal Boris Bugaev, the Soviet minister of civil aviation, ordered the termination of Aeroflot's Moscow-to-Alma Ata supersonic service in May 1978, it looked like the end of the line for the Tupolev Tu-144 supersonic airliner.

Early in 1993, however - 15 years after its last commercial flight - Judith de Paul, president of international trading group IBP, suggested to Rockwell-Collins that the Tu-144 would provide a good development test bed for a US second-generation supersonic airliner. Bill Adams, who was sent by Rockwell-Collins to inspect the Tu-144, considered it "good for the programme", and set about persuading NASA to use it.



That June, Rockwell-Collins met Tupolev at the Paris air show, when Tupolev's director-general, Valentin Klimov, said "-we will build the [research] Tu-144LL anyway; [but] it will take us a long time. With your support it will be quicker". In fact, Klimov, then director of the Tupolev research base at Zhukovsky, and Aleksander Pukhov, chief designer of the laboratory development of the Tu-144, had begun the Tu-144LL programme themselves in 1988.

At that time, Tupolev had four aircraft, each almost brand new in the sense that they had been flown, at most, a little over 100h. Klimov and Pukhov believed that the sustained air-traffic growth of the 1980s would lead to the need for a larger, second-generation, supersonic transport, and they felt that the Tu-144 would be a suitable development aircraft.

NASA chose to use the Tu-144 instead of the Concorde because the Tu-144 flies a little higher and faster. The new US programme called for speeds of Mach 2.4; the Concorde flies at M2.2, whereas the Tu-144 was designed for M2.35 - a big plus for the US team. The Tu-144 is also bigger than the Concorde, with a length of 65.7m compared with 61.6m. Its wing span is 28.8m (25.6m), and it has one-class seating for 150 people (100). With the need for an economical second-generation supersonic transport to carry at least 300 passengers, the extra size of the Tu-144 is an advantage.

With agreement reached to use the Tu-144 as a development aircraft, designer Pukhov started to look in detail at how to solve its problems. A complete overhaul was needed; worse, the RD-36 engines of the Tu-144D had been out of production since 1978 and spares were not available. Pukhov decided to use new engines, a decision which involved considerable redesign work which, combined with the overhaul, meant planning a virtual rebuild, giving the opportunity of installing any test equipment deemed necessary by the US-Russian partners.



By 1993, Russia's aviation industry was in economic crisis, and de Paul personally lent $25,000 to restart the programme. "Without it, nothing would have happened," says Pukhov. "That is why IBP has its name on the side of the aircraft, along with NASA, Boeing, Rockwell-Collins, McDonnell Douglas, Pratt & Whitney and General Electric, the other partners in the NASA-led team."

Pukhov chose the Kuznetsov NK-321 engine of the Tu-160 to replace those of SSSR-77114, the fourth Tu-144D. "The RD36 engines we had at Zhukovsky only had, at most, 20-30h flight time remaining. While the change to the NK-321 involved considerable work, it was not as much as it might have been - the engine intakes and fuselage installation needed only small changes, although the rear nacelle needed substantial redesign," says Pukhov.

"This was not very difficult to do: from about 60% down the length of the engine we had to develop new engine mounts and new nacelles. We actually considered using the Tu-160 at one stage, but the -144D was closer to the aerodynamic ratio needed, so we stayed with it."

The redesign work involved strengthening the wing to take the higher weight and thrust of the new engines; and changes in the fuel, electrical, control and hydraulics systems.

In September 1993, the US-Russia Gore-Chernomyrdin talks included an agreement on the Tu-144 programme, the first major US-Russian aerospace joint programme and in October that year, Tupolev hosted a large US delegation to lay down the requirements of the flying laboratory. Talks continued on and off until June 1994, when NASA and Tupolev signed a $10 million contract to be funded by the US partners, plus the Russian Government.

The joint effort, with US engineers working alongside Russian staff, began in August 1994. The aircraft had been totally dismantled, engines removed and all inspection panels opened; everything was stripped, checked and rebuilt, with the modifications incorporated.

The modifications included the installation of Damien V and VI computers to log the data recorded from around 1,800 sensors fitted to measure temperatures and pressures through the airframe and wings. "The sensors added quite some weight to the aircraft," says Pukhov, "but without the passengers and baggage, there was no problem carrying it."



When the Tu-144LL was rolled out on 17 March, it was expected that it would be flown within two months. Funding delays have meant that eight months have now passed, but the first flight took place on 29 November from Zhukovsky, with Tupolev test pilot Sergei Borisov in command, and the second on 11 December. The flight-test programme requires 32 flights to be completed in Russia. The first two flights were essentially to ensure that everything works on an aircraft that has not been flown for six years. Over the first two flights, take-off weight was to reach 150-160t, speed M0.85 and altitude 33,000ft, and controllability and stability, engine restart, emergency hatch operation, and some auxiliaries were to be checked.

Over the next seven flights the crew will test a range of parameters at subsonic speeds, including engine stability, fuel consumption, and the effects of the loss of one engine. The tenth flight, again subsonic, requires a maximum-range check at a take-off weight of 180t. Two flights will then be used to check longitudinal and lateral stability in take-off, flight and landing configurations.

The supersonic programme begins with the fourteenth flight, when intake settings checks at M1.4, M1.8 and M2.0 are undertaken, with later flights being used to measure settings on acceleration from M0.8 to M max, and on deceleration also; control and stability through the sound barrier up toM1.8; fuel consumption at M1.8-M2.0; service ceiling at a take-off weight of 200t and M2.0 and at levels up to 60,000ft; high-speed control and stability tests and handling quality evaluations, plus specific problem situations including rocking pump failure, afterburner checks and cross- fuel-supply feeds in engine failure situations. The last flight will evaluate emergency descents.

The 32 test flights are expected to take about nine months. When they have been completed, there may be more work in store for the Tu-144LL. The Russian parliament has asked the Academy of Sciences to draw up a programme using the Tu-144LL to study and to solve the ozone layer problems; while NASA is studying the idea of bringing it to California to study sonic-boom problems and is also interested in ozone-layer questions. These could well keep the Tu-144LL, and possibly even a second one, busy for the next three to four years.