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Aviation History
1981
1981 - 1234.PDF
1244 FLIGHT International, 2 May 1981 only holding options on three aircraft (BAe (has Lapa's deposits for three aircraft, hut is not pushing for pro gress payments). In September last year BAe announced that it had two firm orders for 146s from a US commuter, but has not yet revealed the buyer's identity. The first aircraft is due to be delivered in November 1982 and the second in early 1983, so the air line will probably become the first 146 operator. In addition, BAe claims three letters of intent—more news of these is expected at the Paris show. Perhaps the most frequently asked question about the 146 layout is, why four engines instead of just two? A cynic might; reply that the 146 needs roughly 26,8001b of thrust, and that the only way to achieve this with cur rent turbofans is to use four Avco Lycoming ALF502R-3s, But this is only a partial answer. The main advantage of four engines is1 in hot and high performance from short runways—conditions typically experi enced by feiederliners1. In any mulfrengine aircraft, per formance is dictated: by the craft's behaviour after an engine has failed. It does not matter whether an air craft has lost one of two engines on take-off, or one out of four—it must still be able to clear an obstacle at the end of the runway and achieve a safe climb rate. The BAe 146's four turbofans give it a greater reserve of power, allowing it to fly in and out of difficult airfields. Other advantages claimed for four engines include the ability to make three-engine ferry flights without pas sengers, and the retention of more than half the aircraft's electrical and hydraulic power when an engine fails. Threehengine ferry flights would allow an airline to fly its 146s back to base for an engine change, which is much simpler and cheaper than doing it in the field. MILESTONES August 1973 October 1974 April 1977 July 1978 May 1981 July 1981 September 1981 October 1981 August 1982 September 1982 Late 1982 Early 1983 Hawker Siddeley launches 146 Hawker Siddeley postpones 146 Government combines BAC, HS and Scottish Aviation by nationalisation BAe re-launches 146 Roli-out of first aircraft First flight Second aircraft flies Third aircraft flies 146-100 certification First slot for airline delivery 146-200 certification First slot for -200 airline deliveries Most aircraft being proposed or de signed today feature engines under the wing, and the 146 is no exception. Pylon-mounted engines help to relieve bending and torsion felt by the wing during flight, as well as ensuring acceptable stall behaviour. This is not always possible with engines on the rear fuselage. One disadvantage of underwing engines: is that they are more likely to pick up debris when mounted on a low wing. It is partly because of this that BAe's designers have given the: 146 a high wing, especially since it is in tended for roughrfield use. Another reason is that the high wing is about 4 per cent better at generating lift than a low one, mainly because of its uninterrupted top surface. BAe has kept the 146's engines well below the wing, avoiding the need foir flap cut outs next to: their hot exhaust. The high wing allows the inner edge of each flap to farm a snug fit against the fuselage, improving lifting effi ciency. Part of BAe's design philosophy was to achieve the desired 146 per formance with the simplest airframe possible. It has managed to do this without leading-edge silats to improve take-off and landing. Instead, BAe has given the 146 tabbed Fowler flaps, which extend across 78 per cent of the wingspan. Each wing has a one- piece flap, supported by rollers run ning along four tracks. The absence of flap cutouts, endplate effect against the fuselage, high wing, and efficient aerofoil section combine to give the 146 wing a maximum lift coefficient of 3-38. Eliminating leading-edge slats also reduces the pitch changes that have to be balanced-out by the tailplane, allowing BAe to' make do with a fixed onei—'instead of the complexity of an all-moving unit. The 146 has been given a T-tail mainly because: this has the greatest moment arm, and hence allows the smallest size tailplane1. But ^ the arrangement also means that the tailplane is out of the wing down- wash and clear of engine exhaust. In addition, the tailplane acts as an end- plate to the fin and rudder, improv ing their effectiveness. The tailplane uses an inverted Naca section. The wing comprises a series: of aerofoil sections that have been created to. suit the 146's needs, BAe's aerodynamicists have given the tr ailing-edge section a cusp-shaped lower surface. Which produces a more uniform lift distribution along the chord by moving the centre of pres sure aft. The result of this change is that the Mach drag-rise is slightly de layed, allowing a wing with compara tively little sweep at no drag penalty (highly swept wings demand a heavier structure and more complex flying controls). BAe emphasises that this supercritical-type benefit is fairly small for the 146 because of its low cruise speed of Mach 0-7. The other main aerofoil feature is an altered leading edge, intended to prevent airflow separation when the *• flaps are deployed at high angles of attack. BAe derived the aerofoils from both analytical and wind tunnel work. Another part of BAe's strive for The I46's high wing produces about 4 per cent more lift than a low one, mainly because of the uninterrupted upper surface. Engine ground clearance is also better M . jjll J^r P7 f • ••••* fin —H> i "•BE". $
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