One of the displays that has generated a lot of buzz at the Paris Airshow 2011 is EADS' ZEHST concept - a zero-emission hypersonic airliner, that could be whisking passengers from Tokyo to London in under 2.5 hours, by the year 2050. Sitting alongside the ZEHST model, however, is another EADS concept aimed at the more immediate future. It's called VoltAir, and it's a proposed all-electric airliner that could be flying within 25 years.

VoltAir's two next-generation lithium-air batteries would power two highly efficient superconducting electric motors, which would in turn drive two co-axial, counter-rotating shrouded propellers at the rear of the aircraft. The motors would have a relatively easy go of it, as advanced carbon fiber composite airframe design, aerodynamics and low weight would make the airliner as easy to push through the air as possible. As is the case with most proposed and existing electric aircraft, it would also be very quiet.

The batteries would be housed in the lower front section of the VoltAir, where they could be removed and installed just like baggage, at the airport. Recharging would take place when the batteries were out of the aircraft, so planes would simply land, swap out their depleted batteries for charged ones, and take off again. Not only would this arrangement make turnaround times similar to those of conventional refueling, but it would also reduce the weight and technical complexity of the aircraft.

One of the reasons that the sky isn't full of VoltAirs already is the fact that electric motors still don't offer enough power density for large aircraft. With advances currently being made in the field of high-temperature superconducting (HTS) materials, however, EADS sees a potential solution on its way.

While certain materials are able to achieve superconductivity - an electrical resistance of almost zero - at very cold temperatures, others can achieve it at higher (but still cold) temperatures. These are the HTS materials. In the VoltAir's electric motors, HTS wiring would take the place of conventional copper coils, and would be cooled to the necessary temperature with liquid nitrogen. This would result in an almost lossless electrical current, and emissions that would consist of nothing but harmless nitrogen gas.

EADS anticipates that as the technology is developed, high-density superconducting electric motors will actually exceed the power-to-weight ratio of today's gas turbine engines.

The VoltAir certainly doesn't look like today's commercial airliners, but its appearance is about more than just getting attention. The fuselage is designed for an optimum thickness-to-length ratio, which reportedly minimizes aerodynamic drag while maximizing interior space. With the propellers mounted in the rear, they are able to "ingest" the wake from the fuselage, while the wings are able to remain streamlined and engine-free.

Because the weight of the batteries wouldn't change throughout the flight (unlike the weight of a kerosene fuel tank), the rear-mounted motors and the front-mounted batteries would be able to nicely balance the aircraft.

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