Air
Introduction
The key to modern flight was identified by W S Henson in the mid-19th century. Using the principle that the faster air flows, the lower its pressure, his 'double surface' wing design produced lift by curving the upper surface more than the bottom, creating an area of lower air pressure above, and higher pressure beneath.
In 1859, F H Wenham took this new wing design a stage further by showing that a 'high aspect ratio' (a long narrow wing at a small angle) worked best because most of the lift comes from the front of the wing. But there was no successful method of propulsion.
The first powered flight was in 1890, but Clément Ader's 50 metre hop used few of the designs that were to become integral to more sustained successful flight. During the last decade of the 19th century, Otto Lilenthal was taking a different approach and learning the basics of aerodynamics and gliding that would help future aviators to greater success. He died in an accident before moving on to powered flight.
Wilbur and Orville Wright built on Lilenthal's work to produce gliders that could be controlled in flight, making maximum use of the natural properties of the air to minimise the contribution of any power unit. Critically, their machines had moveable wings that could accommodate roll and changes in wind direction – allowing, for the first time, three-dimensional control. A rudder at the back prevented the craft from swivelling around on its axis out of control, while wing warping (bending) and a forward elevator enabled the pilot to compensate for gusts across and from under or above the craft.
In December 1903, at Kill Devil Hill, North Carolina, the brothers made their first powered flight – Orville flying Flyer I for 12 seconds. Frenchman Ferdinand Ferber improved stability to the Wright design by adding a tailplane which his fellow countryman Louis Blériot demonstrated with his flight across the Channel in 1909. Various bi and triplanes followed and 10 years later, in 1919, the Curtiss NC-4 was the first aeroplane to cross the Atlantic.
The propulsion unit was an internal combustion engine – based on the design of Jean Joseph Etienne Lenoir from 1860 – driving a propeller that thrust air backwards. This makes use of the forces that are part of Newton's third law of motion: 'To every action there is an equal and opposite reaction.'
During this time, airships (using a gas lighter than air – hydrogen – to stay aloft) were traversing the globe. But when the Hindenberg crashed burning to the ground in New Jersey in 1937, it took with it most remaining airship credibility.
Boeing produced the first modern-style airliner – the 247 – in 1933. It could carry 10 passengers and travel at 150mph. It included most of the features that remain in use on aircraft to this day: a retractable undercarriage, a single metal fuselage and single, flapped wings. In 1940, cabin pressurisation allowed aeroplanes to travel at greater heights, thus facing less wind resistance and fewer weather problems.
The first jet engine powered the German Heinkel 178 in 1939. But it was Englishman Frank Whittle's design that really took hold of the market, however. Two Whittle engines powered the Americans' first jet plane in 1942: the Bell XP-59 A Airacomet. The jet-powered Bell X-1 was the first plane to fly faster than the speed of sound in level flight when, in 1947, it flew at 760mph.
Jet engines make use of Newton's third law, but produce much higher power. Air enters in the front, a compressor compresses it and pushes it into a combustion chamber where it is mixed with fuel (kerosene) to produce a fast-expanding gas that is thrust backwards, turning the compressor-driving turbine, and then out of a nozzle producing great thrust.
Jet aircraft have become ever more sophisticated and bigger, but still use similar methods of propulsion and design.
Airbus A380
In the commercial world of jet planes, the competition has been between the European joint venture Airbus and US-owned Boeing. Boeing has dominated the skies with its Jumbo 747 since the first of these monsters (747-100/-200) was launched in February 1969. Able to cruise at 640mph for 6,000 miles at 45,000 feet, it was powered by four huge 43,000-pound-thrust Pratt and Whitney JT9D-3 engines. It carried 33 attendants and between 374 and 490 passengers.
But flying is about to change forever. Predicting increasing demand for big aircraft, European aircraft manufacturer Airbus Industrie has created the A380, which will carry 555 passengers in a typical three-class interior layout. It is due to enter service in 2006.
Its statistics are daunting: it has an overall length of 73 metres; a wingspan of nearly 80 metres; an 8,000-nautical-mile range; and super-powerful engines (Rolls-Royce Trent 900 or GP7200 from The Engine Alliance – a General Electric and Pratt & Whitney joint venture) producing a thrust of 70,000lb.
There is also a freighter version, the A380F which will carry a payload of 150 tonnes. Airbus will produce variations on the basic model, such as stretched, shorter and extended-range craft, depending on the market.
But will either the passenger or freight version of the A380 have a market?
Airbus bases its predictions on the assumption that larger aircraft will be needed to cope with congested airports and airspace, rising passenger traffic and growing demand for low-cost travel.
Big aeroplanes mean big money. Airbus forecasts that demand for aircraft with more than 500 seats will put 1,235 into service by 2019. Such a market would be worth $281.8 billion over the next 20 years.
Boeing has responded to this competition by promising a larger, stretch version of the Jumbo (the 747-400X) with more than 500 seats. And some commentators predict that the aviation market will increasingly demand medium-sized craft that can access a greater number of airports than their giant rivals.
Judging the market in such a high-value business is always going to be nerve-wracking, particularly in the wake of the 9/11 attacks on the US, which drove many air passengers away, and with fuel prices always volatile. Environmental concerns are an added burden for the aircraft manufacturer. It claims modern technology and economies of scale employed in the A380 provide 15-20% lower seat-mile costs, 13% less fuel burn and 10% more range than other similar craft. This could have a knock-on effect on reducing costs for airlines and for passengers as well as reducing the emission of damaging pollutants.
Environmentally, space efficiency is a potential winner. Because the A380 will be able to carry more passengers it could ease the increasing congestion in the skies and on the ground in airports. Its designers have also addressed noise pollution, using engine, wing and undercarriage designs to make the craft quieter than its rivals. 'The A380 will generate half the noise level at take-off and carry 35% more passengers than its competitor over distances such as London-Singapore and Los Angeles-Sydney,' A380's manufacturers say.
'Indeed, the A380 will be the first long-haul aircraft to consume less than three litres of fuel per passenger over 100 kilometres (95 miles per imperial gallon) – a fuel burn comparable with the best of small modern turbo-diesel cars,' Airbus adds.
But critics of the craft have reservations. If planes fly with empty seats the competitive edge quickly disappears and bigger planes demand bigger airports, placing greater demands on ground space, leading to the possible destruction of greenfield sites and homes.
Some of the precedents of building giant craft could also serve as a warning. During World War Two, Howard Hughes, pilot and playboy movie producer, created the largest aircraft ever to take to the skies. The HK-1 Hercules Flying Boat, more commonly called the Spruce Goose, was larger than the A380. At 110 metres, its wingspan was 20 metres wider, the largest wingspan ever built. The plane could carry 700 passengers.
Bankrolled by the War Department and his own vast fortune, the flying boat became Hughes' obsession. The Spruce Goose faced many of the same technical challenges that still confront the A380 today and there were many who thought Hughes' bird would never fly.
The Goose's size meant that the cables needed to move flaps and rudders would be too heavy to operate, so Hughes developed a system of hydraulics to give the pilot the power of 100 men to boost the giant control surfaces.
All modern airliners now use hydraulics that work by pushing fluid along a maze of piping to supply enough power to move rudders and wing flaps.
In November 1947, Howard Hughes confounded the sceptics by flying the plane on supposed taxiing tests. But success was short lived. The Spruce Goose never flew again. Lack of customers proved to be its fatal flaw.
However, with airlines such as Virgin Atlantic and British Airways showing an interest, a total of 13 current customers and 139 orders, the future is looking positive for the Airbus A380.
|
