by Acad. Guy SEVERIN, Director General, General Designer, ZVEZDA R&D Center; Mikhail DUDNIK, Senior Expert of the same Center

The Zvezda Scientific Research and Production Center (Tomilino, Moscow Region) stands at the head of the Russian aerospace branch in providing safety equipment for aircraft. In August 2005 its experts finished work on a new life-support system for crews of combat aircraft. The system incorporates an on-board oxygen generator (BKDU) which has passed a complete program of tests and is now in serial production.

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Visitors to the recent International Aerospace Salon MAKS-2005 held in the town of Zhukovsky near Moscow, were watching a breath-taking program of aerobatics (literally-dances in the sky) performed by powerful planes. And only few of them must have thought of how the crews can do their work in the conditions of the rarified atmosphere, dynamic stresses and other adverse "extreme" factors. One of key problems, which is becoming more acute with the more and more complicated flight parameters of modern aircraft, is that of providing the crews with enough oxygen. The problem is dealt with by a special airfield infrastructure and teams of trained specialists. All this involves considerable expenses which can be avoided by only one way-generating oxygen right on board the aircraft.

R&D work on building life support systems for the crews of combat aircraft were initiated by our Center on our own initiative in the year 2000, although the first steps in this direction were made by our aircraft industry back in the 1980s. Unfortunately they failed to bring the expected results because of a lack of financial support. But the main cause seems to be the absence of a clearly formulated concept of building such system as a single on-board complex.

A similar situation emerged in the 1970s when oxygen supply systems were required for the passenger aircraft 11 - 86 and Yak-42. As requested by the Soviet government, we designed, produced and tested, first on pilot airliners, and then put into commercial serial production, a set of oxygen generating equipment, equipment for the crews and passengers in emergency landings and equipment for fire prevention. For the first time in our country chemical sources of oxygen were used for passengers of 11 - 86 aircraft. The technical complex developed by us could be used on new types of planes under construction and also for modernization of all and any domestic passenger airliners.

On beginning development work of life-support systems for crews on the basis of an on-board oxygen generating system for combat aircraft, the ZVEZDA experts adopted a concept of developing a unified set of machinery suitable for all the existing and coming domestic aircraft, including those designed for export to countries with a tropical climate. This approach was supported by the high command of the Russian Air Forces, leading experts of the R&D centers including those named after Alexander Yakovlev, Artyom Mikoyan, Pavel Sukhoi and of the Gromov Flight Research

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Life support system for pilots with on-board oxygen generator BKDU-130.

Institute. At the initial stage we financed the project ourselves and later with the participation of the R&D centers of A. Yakovlev, A. Mikoyan and of the Aircraft-Production Amalgamation in Komsomolsk-on-Amur.

We had no doubts about the possibility in principle of producing an oxygen generating unit with the required parameters and the required preliminary tests were carried out by some domestic plants. Similar kind of equipment had already been tested abroad. The main conceptual solutions were reached during work on earlier sets of oxygen and safety equipment for crews of combat aircraft and foreign experience was taken into account.

Our on-board oxygen generating unit BKDU-130 boosts oxygen level in the compressed air pumped into it by the aircraft compressor. Its principle of operation is based on the use of special synthetic "molecular filters"-zeolites.

Cartriges filled with zeolite sorbent-adsorbers - are connected one after the other with a source of compressed air and the environment. In this cyclic process they absorb from the compressed air, pumped through them, nitrogen, moisture and harmful admixtures, cleaning from these components the oxygen-air mixture by way of periodic association of the sorbent with a more rarified gas media. At certain moments of time air enriched with oxygen is evacuated from the adsorbers and used for breathing of the pilot.

This new system of pilot's life support has no onboard oxygen tanks which makes unnecessary an airport infrastructure and specially trained crews producing oxygen and filling with it aircraft before its tske-off. The length of a flight in this case is not limited by an on-board volume of oxygen because the BKDU-130 unit constantly generates breathing gas mixture. What is more, the size and the mass of such systems require less service time than of gas-cylinder sources. For example, in such sets for aircraft of the Su-30 series the weight difference is almost 60 kg (not more than 32 kg instead of the former 90 kg). The fire and explosion risks are reduced which are usually produced by the presence of pure oxygen and especially when it is under high pressure.

For the unification of the on-board oxygen generating unit it had to be adopted for use in aircraft of different types, with different types of engines and in a broad range of flight regimes. The BKDU-130 can operate in a range of pressures of the supplied compressed air of 80 - 1,000 kPA (relative to atmospheric pressure at the flight altitude) at temperatures -55-+95°C. And the tests revealed that the most "critical" is the "low gas" regime when the pres-sure of the supplied compressed air often drops below

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80 kPA, but the system is functioning well even in these conditions.

Important structural elements of BKDU-130 are its input and output filters whose task is to prevent moisture and aerosols getting into the sorbent and prevent harmful substances from getting into the breathing gas (such as radioactive and biological contaminants).

One of the main components of the system is its gas analyzer which measures the level of oxygen in the produced breathing mixture. This instrument, which uses the method of measuring the partial pressure of oxygen by means of a hard-electrolyte cell on the basis of zirconium dioxide.

All of the aforesaid units are produced as a single apparatus-an on-board oxygen generating unit. The output of BKDU-130 is sufficient for providing enough oxygen for a crew of two. To increase its reliability, the unit has three circuits and remains functioning when one of them fails or is damaged, although in such cases the partial oxygen pressure in the breathing mixture can be somewhat reduced. But in the normal operating regime the built-in control system lights the "oxygen normal" signal. When the "oxygen failure" warning is on the display, a reserve oxygen source located in the catapult seat is activated.

The oxygen supply unit contains an improved valve unit ("automatic lungs") which supplies the breathing mixture into the pilot's face guard without capturing the surrounding air even at low operating pressure in the "low gas" regime of the engine.

Mounted inside the oxygen device, located on the catapult seat, are all elements which ensure normal functioning of the pressure suit in case of cockpit decompression at high altitude. An original sensor of gas consumption has been developed which enables the pilot to control the consumption of gas mixture according to breathing phases.

As has already been mentioned, used as an emergency source of oxygen in case of emergency ejection or in case of BKDU-130 failure is reserve oxygen volume contained in the ejection seat. The seat contains a chemical generator of oxygen which makes it possible to abandon oxygen-supply infrastructure in the airfield.

The new system of life support made it necessary to modernize the equipment and on-board mechanisms for supercharging counter-overload suits of the pilots for maintaining their effective performance at low r.p.m. of the main engines when the pressure of air supplied by compressor drops down.

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The co-authors of the new life-support systems for air crews were the Deputy Chief Designer of the R&D Center named after A. Yakovlev, Boris Prusakov and Deputy Chief Designer of the R&D Center named after A. Mikoyan, Sergei Plyasunkov.

In November 2003 test pilot Roman Taskayev, flying a new combat trainer Yak-130, performed the first test flight within the program of preliminary tests of the on-board oxygen-generating system, which is commercially produced by the SOKOL aircraft factory in Nizhni Novgorod.

In 2004 preliminary, and in 2005 federal trials of the BKDU-130 system were carried out on board the MiG-29M2 aircraft by a team of test pilots of the A. Mikoyan Center headed by its Chief Pilot Pavel Vlasov. Similar tests were conducted at the request of the Aircraft Production Amalgamation in Komsomolsk-on-Amur on board the Su-35UB aircraft. Later on a decision was taken in conjunction with the Sukhoi R&D Center on using the oxygen-generating system on all aircraft of this type which are now being produced.

The factory and federal tests of the new unit have included more than 100 flights on MiG-29, 60 on Yaks-130 and 11 on the Su-35UB planes. The crews praised the quality of the oxygen-air breathing mixture produced by BKDU. They also praised the effectiveness of the modernized system of protection from overloads.

The High Command of the Russian Air-forces recommended the new unified life-support systems with on-board production of oxygen to be installed on fighter and training aircraft. They also suggested studying the uses of such systems on bombers Tu-22M and Tu-160 during their modernization.

Specialists are now studying the expediency of using BKDU-130 for passengers and crews of military transport and civil aviation.

Illustrations provided by the authors and Alexander Djus

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