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Aviation History
1989
1989 - 3675.PDF
engines, is new, while the outer sections, each mounting two engines, are taken from the An-124. Made in traditional Antonov fashion, the wing comprises 11 monolithic sections fabri cated from pressed panels of up to 30m length. The 30m-span tailplane has an area approaching that of the wing of Ilyushin's 11-76 four-jet transporter. The wing, engine pylons, nose-loading door and ramp and landing gear of the An-225 are derived from those of the An-124 and, while the fuselage has the same diame ter, it is 7m longer. The large structural loading carried by the rear fuselage did not allow the installation of a rear loading ramp, as used on the An-124. HIGH-STRENGTH ALLOYS Antonov made extensive use of computer analysis to determine loads on the An-225 structure and to provide the required strength and life while minimising weight. High-strength materials are used, such as zircon alloy for the highly stressed (37-39kg/ cm2) wing-box lower surfaces. This alloy has 50% better fatigue life and ductility than the alloy used in the An-124, and has half the crack growth rate. A different Soviet alloy is used in upper wing panels, tailplane box and those fuselage surfaces formed in one piece where fair static strength, long fatigue life and high corrosion resistance are required. High-strength titani um, together with vacuum arc-melted steel, is used in the undercarriage. As in the An-124, carbon, glass and aramid fibre-reinforced plastics are used extensively, but only for gear fairings and doors, external .load attachment and wing/fuselage fairings and engine nacelles. Flaps, control surfaces, panels and empennage leading-edges are of bonded construction with honeycomb core to increase resistance to vibration and sonic fatigue effects. The largest external payload carried so far is the S Engines and systems are derived from those of the An-124, to save development costs on a small production run. The six three-shaft Lotarev D-18T turbofans each produce 23,400kg thrust with a cruise fuel consumption of about 0.58kg/h/kg thrust. Dual-channel electronic engine control, with mechanical backup, is introduced for the first time, however. Either of the two channels can move the fuel control levers at up to 40°/s and through out the flight the main channel is engaged while the other is on standby. For take-off and landing, however, both channels are engaged and double the rate of response is available. SYSTEM REDUNDANCY The fly-by-wire primary flight control system has four levels of reversion while the second ary flap/slat controls are dual-redundant. Pitch and yaw stability augmentation is pro vided. There are four main hydraulic sys tems, two for backup operation of the wing slats and flaps, which are driven by pairs of pumps on engines one, two, five and six. Single pumps on the other two engines feed hydraulic systems one and four. One of each pair of main pumps is offloaded in flight to extend life. There are three sources of electric power: primary and standby generators on the en gines and auxiliary power units (one in each main landing-gear sponson) and emergency batteries, with two supplies to each of the three busbars. An onboard data collection system moni tors aircraft state and equipment functions, and records crew actions for display and printout. The same system conveys warnings and tracks faults down to line-replaceable unit level. All information is displayed at the flight engineers' stations, but only that requiring prompt crew action is displayed at the pilots' stations. 'iet space shuttle arbiter Buran Each of the An-225's 14 mainwheel pairs— seven per side—extends and retracts inde pendently, virtually excluding the possibility of a wheels-up landing. The four rearmost pairs can be steered to help ground man oeuvring and are centred automatically on lift-off. Gear sensors feed a weight and bal ance system and carbon brakes are fitted. Despite a high degree of systems automa tion—there are no fewer than 34 onboard computers—the An-225, like the An-124, requires a crew of six: captain, copilot, two flight engineers, navigator and radio opera tor. There is sleeping accommodation for a six-man relief crew. The hold is heated and pressurised (to 0.25kg/cm2 differential) and it is equipped for remote cargo observation. When loads require careful temperature and pressure control, an extra crew member is carried. Various external payloads require positive internal temperatures and pressure differen tial to be maintained in flight. In particular, the 8m-diameter, 46m-long, 46t Energia fuel tank can take only longitudinal loads and it must be pressurised for strength when hori zontally mounted above the An-225. For safety, a dedicated system for payload tem perature control and pressure supply is fitted. CARGO HANDLING Equipment for loading and unloading exter nal payloads of up to 250t can be carried internally, as is the case with the 64t Buran space shuttle. Internal payloads of up to 250t are loaded through the nose door. Upper and lower lifting equipment can move loads of up to 20t and 50t respectively about the hold. Above the 7m-wide hold is accommodation for the loading crew. Moving the 30m-long, 24m-span Buran from the factory near Moscow to the launch site at Baikonur is a primary mission for the An-225, but it is by no means the only one. Energia fuel tanks and boosters; lOm-diame- ter, 70m-long petrochemical cracking towers; power-generation turbines; and earthmovers and containers full of Lada cars are also mentioned as possible payloads. The aircraft can carry its maximum 250t internal payload for 2,500km at 850km/h; external payloads reduce maximum range, and cruise speed to 700km/h. At its 600t maximum weight, the An-225 takes off in 3,500m and its range with a typical 200t payload is 4,500km. Surprisingly, the heaviest payload yet iden tified by the Soviets is not Buran—weighing in at 220t including equipment to load and unload it—but an Energia strap-on booster, weighing 240t when its loading vehicle is cartied internally. An unusual role mooted for the An-225 is as the first stage of a two-part reusable space launch system. The aircraft would be used to carry a 200t shuttle to an altitude of 8km- 10km, then release it to climb into orbit. Such a combination would enable payloads of 3t-6t to be placed in orbit. Q FLIGHT INTERNATIONAL 29 November-5 December 1989 35
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