By : Hormuz P Mama

Talk to anyone about futuristic commercial aircraft, and he will rattle off terms like supersonic, and even hypersonic (five times the speed of sound), and the like. But these are still in the realm of science-fiction, which tends to overstate its case in the short term, but is usually short of the mark in the long term.

Our crystal ball shows airliners will not exceed transonic (speeds close to that of sound) performance for many years to come. Today's fastest aircraft in the transonic range is the Cessna Citation X Bizjet at Mach 0.92 (Mach 1 indicates the speed of sound). The fastest airliner is the deceptively ungainly Mach 0.85 Boeing 747. The next supersonic civilian aircraft will be a bizjet (a small luxury business plane) - not an airliner. The emphasis now is not on speed but on lighter and stronger structures, means of reducing aerodynamic drag, etc, and on size, to offer economies of scale.

The conventional helicopter, cruising at 150 kt (a knot is one nautical mile per hour), is at the end of its physical performance limits, due to the inherent aerodynamic limitations of its rotor blades. Against its ability to take off and land vertically, and to hover, it is the most uneconomical means of air transportation.

Soon to come will be the tilt-rotor, which retains the helicopter's best attributes, but flies twice as fast and twice as far - and more economically. The Bell BA 609 tilt-rotor has two large rotors at its wingtips, the axes of which tilt to the vertical for vertical flight and hover, and to horizontal for forward flight like a conventional aircraft.

Its 275 kt cruise and 750 nm (nautical mile) range are closer to those of fixed-wing aircraft, though the operating cost will be more. A major asset is that it can operate off airports, from points close to the city centre. That saves time in shuttling between city offices and airports across congested roads.

To quote test pilot Clay Lacy in Professiona1 Pilot magazine, "This is an aircraft you won't need if you're using airports. Fixed-wing options are still a lot cheaper. And this technology will not likely replace traditional helicopters on typical missions under 100 nm. But a tilt-rotor will be a wonderful aircraft if you have a need for VTOL (Vertical take-off and landing) capabilities and a 275 kt cruise speed".

Bizjets lead the airliners in the application of several technologies. The commercially unsuccessful Beech Starship was the first production aircraft with a fully composite structure. Parent company Raytheon's Premier I, currently in flight test, has an all-composite fuselage but a metal wing. The carbon- fibre, honeycombed fuselage is much lighter but stronger than a metal fuselage. That is how large components of future airliners may also be produced. Premier I will offer low initial and operating costs as it has few components and requires a low production time. In appearance, it is no different from a conventional bizjet; in performance, outstandingly superior.

An aircraft radically different in appearance is the AASI (Advanced Aerodynamics & Structures, Inc.) Strato-crusier, with a wing at the rear and a canard (an extra surface attached to an aeroplane forward of the main lifting surface). In conventional aircraft, tail surfaces produce negative lift or drag. In the Strato-crusier, the wing, canard and tail all produce positive lift. That layout also permits carriage of much fuel in the central fuselage, around the centre of gravity, in addition to fuel in the wing. Result? It can carry up to 12 passengers over ranges of up to 3,250 nm - India-Japan - at Mach 0.80. Its stall speed, runway performance and rate of climb are also exceptional. Like the Premier I, it will not only have a metal wing, but also all-composite fuselage, canard and tailplane. It will have a very light Structure. If its development programme goes well, this could well be the shape of the future for subsonic bizjets.

The aircraft that could have the greatest impact on executive travel will be the supersonic bizjet (SSBJ). Best qualified for the project is France's Dassault - the only one making executive jets as well as supersonic combat aircraft. The project is for a beautifully-optimised eight-seat SSBJ able to cruise at March 1.9 for up to 4,000 nm. Thus it can fly Los Angeles to Sydney with a one hour halt for fuel Tahiti, in just eight and a half hours.

Like the Dassault Falcon 50 and Falcon 900 bizjets, the SSBJ will have three engines for long, over-water flights without the restrictions faced by twin-engined aircraft. These will be modified military engines of about 12,000 lb thrust each, and will not have afterburners. The SSBJ will operate from small business airports like any other bizjet. Price? Roughly $ 50 to 70 m a copy.

Among new developments for next-generation subsonic airliners are "riblets". These are very fine groves over much of an aircraft's surface to reduce skin friction drag - which accounts for about half the total drag. Riblets were inspired by the skin surface of fast-swimming sharks. Flight tests have been most encouraging.

Laminar flow control may be the best way to reduce skin friction drag. By continuous removal of the air in contact with the wing surface by suction through microscopic holes in the first 20 per cent of the wing leading edge, streamlined flow can be maintained over much of the wing. Airbus Industrie is trying it out on the vertical fin of an A-320.

New materials of construction continued to be developed. The fixed leading edge of the new Airbus A-340-500 and 600 wing will be of glass-fibre reinforced thermoplastic composite material. Such components will be 20 per cent lighter than today's thermosetting material, and will be quicker and easier to fabricate. They will also be more damage-tolerant, and will be easier to inspect and repair.

While aluminium alloys and steel will continue to be used, the light but very strong aluminium-lithium alloys will find increasing usage. A totally new material is glass fibre-metal laminate, which will offer good mechanical properties and excellent fire resistance. It will be used in the Airbus 3XX.

Fly-by-wire controls, pioneered on Concorde, gained widespread application for the first time on the A-320. These are now being applied to increasingly smaller aircraft. World leader Lucas Aerospace will supply the world's first complete fly-by-wire control system with no mechanical back-up control for the Fairchild 728 JET regional aircraft. Pilot commands are transmitted through electrical signals, and via a computer that prevents aircraft physical limitations like speed and "g" forces being erroneously exceeded.

The next major civil aviation development is the Airbus industry A 3XX - a full-length double-deck, 550-seat (three-class) 550-tonne aircraft. It will be much bigger and have 40 per cent more cabin area than the Boeing 747. Direct operating cost will be about 15 per cent less. Passengers will have wider eats, and lower-deck sleeping areas, boarding and deplaning will be faster, with direct links by air-bridges to the upper deck Entertainment facilities will be unprecedented, along with business centres, lounges and the like.

While no faster than the B 747, the A-3XX will be significantly superior aerodynamically, structurally and economically. It will set new standards of maintainability and reliability. Problems? One hopes there is an adequate market for this $ 12 billion investment. Incidentally, it will not be the largest aircraft ever made. The solitary six-engined Antonov An-225 Mriya freighter weighs 600 tonnes and is also much larger.