IELTS Academic Reading Practice Test 163

An airship is a powered balloon: a long, streamlined envelope filled with a gas that is less dense than the air around it, driven by engines and steered by fins at the rear. The lift comes not from wings or rotors but from buoyancy, the same principle that keeps a ship afloat, and it is therefore independent of speed. An airship can hover, fly slowly and land almost anywhere, qualities that aeroplanes have never matched. The gas that gives the most lift is hydrogen, the lightest element, which produces about a kilogram of lift for every cubic metre of envelope; helium, which is safer, gives slightly less.

The first person to combine a steam engine with a balloon was the French engineer Henri Giffard. In 1852 he flew a hydrogen-filled airship about 44 metres long from Paris to Trappes, a distance of some 27 kilometres, at a speed of perhaps ten kilometres an hour. The engine was small, and although the craft carried a rudder, its speed was too low to make headway against anything more than a gentle wind. Giffard's flight proved that powered flight was possible; it also showed that a practical airship would need far more power.

Progress came slowly. The first airship to make a controlled flight and return to its starting point was La France, built by two French army officers, Charles Renard and Arthur Krebs. In 1884 it covered about eight kilometres on a circular course, driven by an electric motor whose power came from heavy batteries. Electric propulsion was clean and quiet, but the weight of the batteries limited both speed and endurance, and most later designers went back to engines that burned fuel.

The decisive figure was Count Ferdinand von Zeppelin, a retired German army officer who believed that a rigid frame was the answer to the weakness of the balloon. His airships kept their shape because a lattice of aluminium struts and wires held the envelope in tension, and the gas was contained in a series of separate cells, so that a leak or a puncture would not deflate the whole craft. The first Zeppelin, the LZ 1, measured 128 metres and carried two Daimler engines. It flew over Lake Constance on 2 July 1900, but it was underpowered, it was damaged during the trials, and the money ran out.

Zeppelin's fortunes changed after a disaster. In August 1908 one of his airships, the LZ 4, was caught in a storm and destroyed at Echterdingen, near Stuttgart. A public subscription was launched, and a wave of national enthusiasm produced more than six million marks, enough to found the Zeppelin Foundation and to build further craft. In 1909 the company founded DELAG, the world's first airline, which carried some 34,000 passengers on about 1,500 flights before the First World War without, it appears, a single serious injury.

War changed the purpose of the airship. German naval and army airships flew reconnaissance missions, carried supplies and bombed British cities, often at heights that defending aircraft and guns could not reach. The raids frightened the public, but their military value was limited. The development of incendiary ammunition, faster fighters and better anti-aircraft guns turned the hydrogen-filled airship into an easy target, and losses mounted until sustained raids had largely ceased by 1917.

After the war the airship enjoyed a brief second life. In July 1919 the British craft R34 made the first east-to-west crossing of the Atlantic by air and then returned to England, completing the first double crossing. Ten years later the German LZ 127 Graf Zeppelin, commanded by Hugo Eckener, flew around the world in 21 days, watched by large crowds at every stop. The Graf Zeppelin later made flights over the Arctic for scientific research, and it covered more than a million and a half kilometres before it was broken up.

The largest airship of all was the Hindenburg, which entered service in 1936 and was 245 metres long. Its hull had been designed to use helium, a gas that will not burn, but the United States was then the world's leading producer of helium and had restricted its export, so the ship was filled with hydrogen instead. On 6 May 1937, as the Hindenburg came in to moor at Lakehurst, New Jersey, it caught fire and sank within a minute. Of the 97 people on board, 62 survived; a member of the ground crew also died. Newsreel film of the burning airship was shown in cinemas around the world, and passenger airship travel ended almost at once.

Rigid airships disappeared, but the smaller non-rigid balloon, known as a blimp, survived. The United States Navy used blimps for anti-submarine patrols and convoy escort during the Second World War, because they could stay airborne for long periods and could match the speed of a slow ship. Later blimps were used mostly for advertising and for television pictures at sporting events, and the few modern airships that now carry paying passengers are filled with helium.

A wireless charger is a flat pad on which a phone is laid, with no plug and no socket. The idea is older than the telephone: the possibility of moving energy through space without a wire was demonstrated in the nineteenth century, and electric toothbrushes have been charged without contacts for decades. What is new is the scale. Hundreds of millions of devices now charge inductively, and the same principle is being applied to cars, medical implants and industrial machines. Almost all of this charging works by magnetic induction, the phenomenon that also explains how a transformer functions.

The basic mechanism was described by Michael Faraday in 1831. When an electric current flows through a coil of wire, it produces a magnetic field; if the current is alternating, the field grows, collapses and reverses many times a second. Place a second coil in that changing field and a voltage appears across its ends, driving a current if a circuit is complete. In a wireless charger the transmitting coil is driven by an alternating current, and the receiving coil inside the device converts the field back into electricity. The two coils behave like the two windings of a transformer whose core has been replaced by air.

The first mass-market application was not the telephone but the electric toothbrush. A toothbrush is used in water and must be rinsed, so exposed metal contacts would corrode and could give a shock. Sealing the handle completely solves both problems: the two coils are separated by a wall of plastic, and the current passes through it. The same logic explains why wireless charging appeals to designers of devices that must be waterproof, from smart watches to surgical instruments.

For phones, the important development was agreement on a common standard. The Wireless Power Consortium, an industry group, was formed in 2008 and published a specification called Qi, named after a Chinese word for vital energy. Early Qi chargers transferred about five watts; later versions carry 15 watts or more, enough to charge a phone quickly. A rival standard, AirFuel, once promised greater freedom of placement, and the competition between the two delayed adoption in some markets. Standardisation matters because a charger that works with one brand of phone may not work with another.

The limitation of simple induction is distance. The field from a coil weakens rapidly, so the receiving coil must sit within a centimetre or two of the transmitter. A more flexible approach is magnetic resonance. If two coils are tuned so that they resonate at the same frequency, energy can pass between them across a larger gap and with less exact alignment. In 2007 a team at the Massachusetts Institute of Technology led by Marin Soljačić used this method to light a 60-watt bulb from about two metres away, with roughly 40 per cent of the power reaching the lamp.

That efficiency figure points to the central difficulty. Even a well-designed inductive charger loses a tenth or more of the energy it draws, and the proportion falls sharply when the coils are badly aligned or further apart. The lost energy appears as heat, which warms the device and the pad and, in the case of a phone, can shorten the life of its battery. Stray fields also heat nearby metal: a coin or a bunch of keys lying on a charging pad can absorb energy, and the currents induced in it may make it hot enough to be a hazard. Good chargers therefore include foreign object detection, which cuts the power when anything metallic is present.

The comparison with a cable is sobering. A cable can deliver a hundred watts or more with almost no loss, which is why laptops and fast-charging phones still use one. Wireless charging is chosen for convenience and for durability rather than for efficiency. It allows a device to be sealed against water and dust, it removes a connector that can wear out or fill with lint, and it turns charging into a matter of putting something down rather than hunting for a lead. For an electric car, a pad buried in the parking bay delivers around 11 kilowatts and saves the driver from handling a heavy cable in the rain; bus operators and taxi firms have tested the idea at depots and ranks.

Research now aims at distance. Several groups are experimenting with relay coils that pass energy from one to the next, with fields shaped by metamaterials, and with beams of ultrasound or radio waves. Each method faces the same constraints: efficiency falls with range, and regulators impose limits on the strength of fields to which people may be exposed. A charger that filled a room with usable power would need either very large coils or a level of exposure close to those limits, and no such product is yet on sale.

Wireless power is therefore likely to spread unevenly. Where a device is small, sealed and replaced often, the freedom from contacts is worth the lost energy. Where large amounts of power must move quickly, the cable will survive. The most interesting work is happening in the space between: medical implants that recharge through the skin without a wire emerging, robots that top up their batteries by parking over a plate, and sensors that never need a human to plug them in at all.

Few proposals in commercial aviation are discussed as cautiously, or as persistently, as the idea of taking one of the two pilots off the flight deck. Manufacturers, some airlines and a number of regulators have studied a model in which a single pilot flies the aircraft during the cruise while the second rests in the cabin, ready to return if anything goes wrong. The appeal is easy to see. I want to argue that the case has been accepted too quickly.

The arguments for reducing the crew are largely economic. A long-haul flight carries two pilots, sometimes more, and their salaries, training, hotels and rest facilities all cost money. Airlines concede that the saving would be modest on a single flight, but margins are thin and every item counts. Shortages matter more. Manufacturers' forecasts have for years predicted that the world will need far more pilots than it is training, and a fleet that doubles in size cannot be crewed in the present way unless training expands enormously. If automation can replace one of the two people on the flight deck, the shortage becomes easier to manage.

Both sides of the argument tend to exaggerate how much of a flight is already automated. On a modern airliner the autopilot is engaged a few minutes after take-off and remains in control until the approach, and at some airports the aircraft can land itself. Computers manage the engines and much of the navigation. But this is not autonomy. The machines hold a trajectory the crew has chosen; they do not decide where to go, or whether a strange noise is serious. Even an automatic landing depends on a pilot who set the systems up and who takes over if the aircraft drifts off course.

The most underrated difficulty is that people are poor at watching and doing nothing. Studies of vigilance dating from the Second World War show that someone asked to monitor a display for a rare event misses more of them as time passes. Cruise is the phase in which nothing happens for hours, and the phase in which a single pilot would be alone. Two pilots talk to each other and notice when a colleague has misread a clearance. That conversation is a safety system in itself, and it appears on no diagram of the aircraft.

Incapacitation is the objection most often raised, and it is real but secondary. A pilot who loses consciousness cannot be replaced by a colleague asleep in the cabin, and the automation will hold the aircraft steady without deciding anything. Such events are rare, but the stronger objection lies in the ordinary workload of flight.

The Germanwings crash of 2015 changed the shape of the debate. A co-pilot locked the captain out of the cockpit and flew the aircraft into a mountainside, killing all 150 people on board. The response in Europe was a rule requiring two crew members on the flight deck whenever one pilot leaves, a rule that cost airlines money. The case is not an argument for removing the second pilot; it is an argument that the second person is a check on the first. Automation cannot notice that a colleague has become a threat, and no controller watching a screen abroad can open a locked door.

Air France 447 offers the opposite lesson. In 2009 an Airbus A330 flying from Rio de Janeiro to Paris entered a storm; its speed sensors iced over, the autopilot disengaged and control passed to two pilots who had been monitoring rather than flying. Confused by conflicting warnings, they never recognised that the aircraft had stalled, and it fell into the Atlantic with the loss of all 228 people on board. The official investigation blamed a combination of technical failure and the crew's failure to understand what the aircraft was doing. What failed was the handover.

Ground-based support is offered as the answer. A single pilot would not be alone, the argument runs, because a team on the ground would watch the flight and could take control remotely. The analogy with military drones is instructive: a large drone is flown by a crew of several people, and its accident rate has been higher than that of manned aircraft of similar size. A controller monitoring a dozen flights, with a satellite delay of a second or more, is not a substitute for a colleague in the next seat.

Regulators have been cautious for exactly this reason. Certification rests on the assumption that systems fail and that someone must be there to cope when they do, and no authority has yet approved routine single-pilot operation of a passenger jet. Public trust matters too. Passengers already accept a great deal of automation, but they might reasonably ask what has been gained by removing the second pilot, when crew pay is a modest item in an airline's costs.

I am not arguing that the second pilot is permanent. Automation has already replaced the flight engineer, the navigator and the radio operator, and its record is impressive. But each of those roles was removed when the machine could do the task better and the failure was visible. The second pilot exists not to fly the aircraft for hours but to notice, to disagree, and to take over when the automation has done something nobody expected. Until machines can do that, the saving is a false economy, and the burden of proof lies with those who would make it.