雅思阅读素材积累：No more whirly-splat

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　　雅思阅读：No more whirly-splat

　　ALTHOUGH rare, engine failure is a stressful thing for a helicopter pilot
to have to deal with. The pilot of a fixed-wing aircraft that loses power can at
least rely on those wings to provide him with lift until his plane's forward
velocity falls below its stall speed. A helicopter, by contrast, derives both
propulsion and lift from its blades. If they stop rotating, a rapid and terminal
encounter with the ground beckons.

　　To prevent that, the blades of most helicopters have a special clutch that
disengages them from the engine if the engine stops. The pilot has then to
change the pitch of his craft to allow it to enter a mode called autorotation,
in which the rush of air as it descends keeps the blades whirling, thus
providing lift that slows the fall. The transition to autorotation is perilous,
though, because it involves a reversal of the airflow through the blades. And
even if he survives that, the pilot has to perform a second manoeuvre, known as
flaring, just before he hits the ground. This involves pitching the machine's
nose up, in order to reduce its forward velocity and increase the speed of
rotation of the blades—and thus the amount of lift they provide—to soften the
landing.

　　Both of these maneuvers would be less hazardous if the pilot could call on
a second source of power to turn the blades for a few seconds while he was
performing them, and Jean-Michel Billig and his team at Euro copter (part of
EADS, an aerospace and defence group) hope to provide just that. They are
introducing into helicopters the fashionable concept of hybrid-electric
drive.

　　Electric motors provide lots of torque—exactly the sort of twisting action
needed to turn rotor blades. Mr Billing's team have therefore fitted one of the
firm's AS350 light helicopters with such a motor, and some lithium-ion batteries
to power it. They are now testing the arrangement to work out how much power is
needed to keep the craft aloft during the transition to autorotation, and during
flaring. Mr Billig thinks Euro copter will be able to offer the system
commercially in about a year's time.

　　That raises the question of whether it might be feasible to build an
all-electric helicopter. At the moment, the answer is no. As with cars, the
amount of charge a battery can hold is insufficient for robust, everyday use of
the vehicle without the security blanket of an internal combustion engine. But
batteries are improving, and if they were good enough then an electrically
powered helicopter would (like an electric car) be a more elegant solution to
the problem of locomotion than the serial explosions that keep an
internal-combustion engine ticking over.