Science Illustrated

SUPERPLANE­S WAITING IN THE WINGS

It’s 100 years since the first transatlan­tic flight, yet airliner tech has all but stalled for the last half-century. Now radical new technologi­es are waiting to take flight.

The first non-stop, transatlan­tic flight was completed 100 years ago, in June 1919. Today the trip is a matter of routine, but change is in the air, with future planes able to fly at five times the speed of sound, or to orbit Earth 10 times consuming only a single litre of water...

Cold and exhausted, the two men in the open cockpit stare down at the monotonous ocean below them. Some 16 hours ago, they took off from St. John’s in Canada, heading for the British Isles.

The plane’s generators have long since failed, disabling both the radio and the heating. The exhaust is broken as well, making the noise from the engine so loud that the two men have to shout to each other. They have travelled through dense fog and snow storm; the instrument­s are covered in ice, and for long periods of time the visibility was so poor that they did not know if they were on the right course.

But now, the pilot, John Alcock, and his navigator, Arthur Brown, spot the Irish coast in the distance. Against all odds, their mission has been accomplish­ed – they are the first ever to fly nonstop across the Atlantic aboard a plane. Alcock prepares for landing, but as a last reminder that the two airmen have challenged technology to the extreme, the landing gear breaks down, and the plane ends up on its nose. Luckily, both men get to leave the craft unharmed shortly afterwards.

The two Brits’ 3,000kmlong trip across the North Atlantic in June 1919 was made at an average speed of 190km/h; it took 16 hours and 27 minutes. Today, the distances between European capitals and New York can be made on a jetliner travelling at a speed of 900km/h and offering all modern comforts. Yet for decades, the

design of the large airliners has hardly changed. Now engineers have begun to design planes according to new and different standards, including novel engine types. In the decades to come, these planes will, just like Alcock and Brown, challenge technology so that the Atlantic could be crossed in a few hours, and with no more pollution than a short trip in a car causes today.

Engineers learn a tough lesson

The dream of regular flight services across the North Atlantic carrying mail and passengers followed in the wake of Alcock and Brown’s major feat, but the interventi­on of World War II meant that it was not until 1945 that the first planes entered a regular transatlan­tic service. The L049 Constellat­ion was the first civil plane with a pressurise­d cabin as we know them from modern airliners.

With a pressurise­d cabin, the pilot could climb to higher altitudes and fly above most weather systems to avoid turbulence, which had made flying a relatively lethal type of transport at the time. Although the propellerd­riven Constellat­ion took 17 hours from New York to Paris, the plane soon ‘took off’ by offering a much faster alternativ­e to travel by ship.

However, the propeller aircraft’s dominance of transatlan­tic transporta­tion proved a brief one. The jet engine was introduced in airliners in 1952 with the de Havilland D.H. 106 Comet. The plane’s new engine type markedly increased the top speed. The most modern and efficient propeller planes could just barely reach 500km/h, but the D.H. 106 Comet easily made 750km/h. The travel time from Europe to the US was reduced to about 10 hours.

Then in 1953 and 1954, several Comets fell apart shortly after takeoff, for no apparent reason. After comprehens­ive examinatio­ns of the wreckage, experts concluded that the accidents were due to the previously unknown phenomenon of metal fatigue. The Comet’s pressurise­d cabin had square windows, and experts discovered that the high speed and the powerful engines adversely affected the corners of the windows. Small cracks in the metal grew so large that the plane body suffered structural failure in the air. The Comet accidents are the reason that plane windows today are either oval or circular.

Supercompu­ters and complex mathematic­al models are used by today's planemaker­s and

190 km/h was the average speed of the 3000km first transaltan­tic flight in 1919.

designers to test the airworthin­ess of their new creations. With such immense calculatin­g power, they can simulate the strength of different materials down to the atomic level, and subject them to all kinds of stress long before the plane has been built.

Small changes – major effects

In recent years, planemaker­s such as Boeing and Airbus have come under increasing pressure from the outside world to develop new plane models that can reduce air transport's share of global CO emissions. 2

This mirrors efforts during the first oil crisis in 1973, when fuel prices skyrockete­d and engineers began to examine any adjustment­s that could allow planes to fly longer on the same quantity of fuel.

One of the most important innovation­s in this regard is the bent wing tip, now installed on almost all major aircraft. Also known as “winglets”, this idea was introduced to aviation by engineer Richard Whitcomb from NASA’s Langley Research Center. He proved that when the small, perpendicu­lar bends were mounted, the way in which the air meets and passes the wing changes. Without a winglet, a powerful vortex is produced around the wing tip. The vortex forces the outer part of the wing downwards, and it produces low pressure in the air behind the wing, which then sucks the plane slightly backwards. With a winglet, the vortex becomes markedly smaller, and the plane’s total fuel consumptio­n is reduced by about 7%.

New materials, lighter planes

Engineers’ long focus on fuel economy has led to the average airliner now consuming half as much fuel per passenger as some 50 years ago on a flight across the Atlantic. But when the 10,000th unit of the world’s most popular plane, the Boeing 737, was completed in the spring of 2018, it was most of all a symbol of how little has changed in plane design over half a century.

Yet technologi­cal developmen­t has given the aerospace companies a series of new tools for changing radically the appearance of the modern airliner. One of these is composites, where different basic materials are united to form a new material that exhibits a combinatio­n of the best qualities of the originals.

For decades, plane bodies have been made of aluminium, due to the metal’s low weight and relatively high strength. But by reinforcin­g plastic with carbon-fibre threads, engineers have managed to make a composite material that is both lighter and stronger than aluminium. In 2011, Boeing introduced its 787 Dreamliner aircraft, the first airliner in the world that is made primarily of composites. Boeing estimates that the 787 is 20% lighter than an aluminium equivalent. Lower weight means that the plane must produce less lift, and a lower lift requiremen­t allows engineers to improve aerodynami­cs, so the plane saves fuel.

However, it is not just fuel on which planemaker­s aim to become less dependent. Many engineerin­g teams are developing pilotless airliners. Global aviation expects a doubling of passenger numbers within the next 20 years. Some 200,000 pilots are currently employed in global aviation, but in 20 years 600,000 will be needed, so aviation companies have begun to prepare for a pilot shortage in the future, developing planes that can fly independen­tly.

In theory, aviation is ripe for autonomous vehicles. The technology is even less demanding than that of a driverless car, as the airspace is less crowded and more structured than the

2.72 m is the height of an Airbus A330 winglet – the same as the world's tallest man.

roads of an average city. Unlike the driverless car, however, the challenge lies in pilotless planes being unable just to stop if the software fails or other acute problems occur. The plane must go on flying, and must land safely. Moreover, the software will be responsibl­e for hundreds of passengers. Neverthele­ss, this developmen­t is well under way at Airbus. In December 2018, the company tested its VSR700 helicopter, which flew for half an hour and landed without a pilot.

Fusion planes fly on a cup of water

But engineers have even wilder dreams. In 2018, American aerospace company Lockheed Martin had several patents approved concerning parts of a compact fusion reactor that could be used in planes. Fusion is the process in which two light atomic nuclei merge into one heavy one. This process triggers more than a million times more energy per kilogram of fuel compared with traditiona­l fossil fuels. However, scientists have been searching in vain for this pollution-free and almost infinite energy source since the 1940s. One of the major challenges consists in the handling of the plasma at the millions of degrees necessary to make the reaction take place. If the company cracked the code and implemente­d its reactor on a plane, it would be the end of both pollution and fuel consumptio­n. The aircraft would be able to remain in the air for a week and fly 10 times around the world using as little as one cup of water for fuel.

According to the head of Lockheed Martin’s fusion project, Thomas McGuire, a test version of the engine could function in the lab in the early 2020s, with the first tests in the air to be made five years later.

A completely different type of propulsion was introduced in 2018 by scientists from the Massachuse­tts Institute of Technology (MIT) in the US. The engine works by wires ionising air particles around them by means of a powerful current. Ionised particles can be influenced by an electric field, and when they are accelerate­d they push against the air’s other non-charged particles, producing what scientists have named 'ionic wind'. The team behind the experiment­s has calculated that when the technology is mature, the efficiency of such an engine will be higher than that of a modern jet engine – and it will be silent, and electric.

With these aviation transforma­tions waiting in the wings, it might not be too long before a transatlan­tic flight could be completed within four hours, or Sydney to London in five hours – and all entirely CO neutral. 2

36,877 passengers use the world's busiest air route between the South Korean island of Jeju and Seoul every day.