What is it about the single-seater Sunseeker II that drew a steady stream of visitors to the solar-powered airplane on display at the Green Air Show in Paris recently? Could it be the bluish flash of solar cells on its huge wings, or the inviting open cockpit, or maybe even the teetering propeller to the rear? Perhaps it's a delightful combination of gorgeous form and emission-free function that turned all those heads. With a two-pilot version coming soon, Gizmag took the opportunity to have a closer look.

Hang gliding veteran Eric Raymond first developed a solar-powered airplane in the late 1980s and used it to successfully cross the U.S. in 1990, spending some 121 hours in the air. Following a long list of refinements and modifications, an almost entirely new airplane was created some years later - Sunseeker II. The most recent change has been the implementation of dipped wing tips to allow for runway taxi. During flight, the new tips are pulled flush with the rest of the 17 meter (55 foot) wingspan.

Sunseeker II has solar cells integrated into the structure of the wing rather than being bonded to its surface. Contained within the wing structure are 48 Lithium Polymer battery cells which power the 5kW electric motor both during take-off and when gaining altitude, after which the pilot has a choice. Once at cruising altitude, he can either continue to drain the batteries, switch to solar only, or simply glide. The motor spins a "unique teetering propeller" to reduce vibration, working somewhat similarly to a helicopter's teeter hinge.

Its dry weight is just 120kg (264 pounds), it has a maximum speed of 160kph (just under 100mph) and a cruising speed of 65kph (about 40mph). The cockpit features tinted sliding windows that cater to in-flight photographic opportunities, and a panel which includes readouts for airspeed, GPS, battery/solar cell management and compass and horizon instruments.

Whilst the single-seater Sunseeker II is impressive enough, Raymond and his team are currently working on a two-pilot solar-powered aircraft, continuing the legacy by naming it Sunseeker III.

There will not just be enough room for two people in the new airplane, but dual controls too, the idea being that on long-haul flights one pilot can fly while the other rests. Only the cockpit was on display at Le Bourget, which is probably just as well because Sunseeker III is heading for a massive 23 meter (75 foot) wingspan. A rendering of the instrument panel sat at the front of the display model as an indication of things to come.

The Sunseeker III team is said to be using 22.8 percent efficient SunPower solar cells and a 20kW electric motor. Raymond told Gizmag that he hopes to have a motor contribution from solar in the region of 5kW. The position of the collapsible propeller has also changed from earlier aircraft, now being placed above the wings and in front of the empennage to help reduce vibration.

Development of the Sunseeker III is looking good for a 2011 test flight. More information is available from the Solar Flight website.

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