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Aviation History
1986
1986 - 1414.PDF
ft*" _ ' JSjK »~ 1 .. i* -1* LJ1_ Corporate flying, Italia Of all the new-technology corporate turboprops being developed, the Rinaldo Piaggio P. 180 Avanti is shaping up as the fastest and most fuel- miserly, if claims by the Italian manu facturer are to be believed. Piaggio's aim sounds familiar—to make a 6-9 seat busi ness aircraft that will fly as fast as a corporate jet, and retain the fuel efficiency of the turboprop—but its approach is unorthodox. The Italian firm is opting for a unique combination of aerodynamics and structural design. It claims that the resulting aircraft will be able to cruise at 400kt, will burn around half the fuel of a jet and, at $3-1 million, will cost about half the price. With the Avanti's first flight imminent, it may not be long before Piaggio's claims can be substantiated. The Avanti is one of four aircraft intended to plug the gap between turboprop and jet aircraft. The Lear Fan seems to have failed. Avtek is having fund ing problems. The Beech Starship, the remaining contender, faces a one-year delay. Avanti differs from all of these. While they are all composite, Avanti is mainly metal, using novel three-surface aerodynamics involving a wing, foreplane, and tailplane. Piaggio claims to have hit on a configuration which beats other corporate aircraft planned or flying, both on fuel-burn and comfort, and is to patent the design. Piaggio hopes to capture 10 per cent of the turboprop market and convert some jet users to propellers. The project is going to cost $125 million to certification, expected The Piaggio P. 180 Avanti combines novel aerodynamics with sophisticated metal construction in a dramatic departure from tradition. Alan Postlethwaite reports, with a Flight cutaway by John Marsden. next year, and since the current general- aviation slump could jeopardise a market launch at that time, it is an expensive gamble for a firm which made L145 billion ($93 million) in sales last year. The Avanti project began more than six years ago at Piaggio's Finale Ligure design office on the Mediterranean coast. A canard configuration was one of the first to be considered, being inherently more efficient (aerodynamically) than a conventional aircraft with a rear-mounted tailplane, it is said. In each configuration the tailplane or foreplane acts to counter the nose-down pitching moment gener ated by the combination of wing lift and aircraft weight. A conventional tailplane at the rear is rigged to produce a down force, to achieve this. However, that down force acts in opposition to the wing lift, and compels the aerodynamicist to enlarge the wing, so that the net lift on the wing-tail combina tion is unimpaired. This means more drag and reduced cruising efficiency. 42 In a canard, the foreplane is ahead of the wing and produces an upload. This enables the main wing to be smaller, with a consequent reduction in drag and an improvement in cruise efficiency. A prob lem is that the foreplane reduces stability, and that is where the third surface—a tailplane—comes in. Avanti's tail provides stability, but is expected to produce little lift or downforce in the cruise condition. Piaggio's chief aerodynamicist, Alessandro Mazzoni, declares, "the pure canard with a stability augmentation system is most efficient, but the three- surface configuration comes close". He claims that canards lose out against the three-surface Avanti because their wings are unable to carry such effective high-lift devices, and so must be increased yet further in size for good landing performance. Stability augmentation is too expensive a feature for corporate aircraft, says Mazzoni. In the USA Nasa has compared three- surface layouts with a conventional design. In model tests, a three-surface layout was fitted with twin wing-mounted pusher engines. The conventional layout had twin tractor engines. Nasa reported improved lift at all angles of attack up to the stall on the three-surface windtunnel models, and a substantial reduction in drag. The wing layout and the engine installation contributed to the improvements. Nasa also noted that, in a three-surface layout, the aft location of the main wing results in it producing a large, destabilising FLIGHT INTERNATIONAL, 21 June 1986
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