“Within this decade, we will certainly see hybrid electric aircraft entering the market,” says Frank Anton, who heads the hybrid aircraft efforts at Siemens. Four-seat hybrid aircraft are likely within that time frame, he says, but even 19 seaters are possible before the decade is out. Anton predicts that eventually we will see 100-passenger hybrid aircraft that use half as much fuel as today’s airplanes.
Boeing is taking this a step further with a concept for hybrid airplanes the size of 737s, which can seat more than 150 passengers, although it’s unlikely these will come into service before 2030. EADS, the parent company of Airbus, has also developed a conceptual design for passenger airplanes that fly exclusively on electricity, although the range of these aircraft would be limited.
Higher power density batteries, lighter electronics, superconductors that will enable smaller and more powerful engines, lighter and stronger materials will all help enable larger and more efficient hybrid and electric aircraft.
Flying hybrid: This two-seater electric-gas airplane may be the first of many to take to the skies. It has a range of 900 kilometers (600 miles)
The amount of energy that batteries can store is steadily improving, and this looks likely to continue as they’re developed for use in portable electronics and electric vehicles, Bradley says. Meanwhile, the technologies needed to integrate batteries and electric motors with conventional engines are getting smaller, lighter, and more efficient. Siemens demonstrated an earlier version of its hybrid airplane in 2011, but it was too heavy to be practical. For the new plane, Siemens decreased the weight of the electric motor, power electronics, and gears by 100 kilograms to bring its cargo and passenger capacity up to the level of similarly sized small planes.
In airplanes, a hybrid electric design improves efficiency mainly by making it possible to use a relatively small gas-powered engine designed to run at its most efficient at cruising speeds. The battery and electric motor provide the extra power needed for takeoff and ascent. The batteries also make it possible to recover energy during descent much the way hybrid cars capture energy during braking (propellers spin a generator). And, as batteries improve, they will provide more and more of the energy on board.
Electric motors confer other advantages. They can be mounted in unusual places on an airplane, which can be used to improve aerodynamics. They can also be steered: angled upward, for example, during takeoff to get a plane off the ground faster. In flight, the motor could be pointed left or right to steer the plane, eliminating the need for a rudder. These design changes, together with the efficiency of the hybrid propulsion, could help decrease fuel consumption by half.
How fast electric propulsion is adopted depends mostly on the development of the batteries. EADS’s electric airplane plans call for a battery that can store 1,000 watt hours per kilogram, which is about five times more energy than a typical lithium-ion battery. New battery chemistries like lithium-air and lithium-sulfur could provide more capacity
SOURCE - Technology Review
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