Sunseeker Seeks New Records
By Bill Moore
Imagine flying an aircraft whose power-source is 93 million miles away. An aircraft so clean that it generates no air pollution and little noise pollution.. And according to its creator and pilot, birds often soar within a few feet of it.
You don't have to imagine. It's very real and its creator and pilot is not unfamiliar with the electric vehicle industry. AC Propulsion's Alan Cocconi, the engineering genius behind the tzero and other electric automobiles, contributed to the development of Eric Raymond's solar-powered sailplane, the Sunseeker, the first solar-electric aircraft to fly across the North American continent. The trim and tanned Raymond also has flown Aerovironment's Solar Challenger. He's even been at the controls of the current record holder for the fastest -- at less than 35mph -- solar aircraft, one developed in Munich, Germany.
Raymond told EV World that it was the Germany aircraft, which weights a mere 52 pounds and requires only 250 watts of solar-energy to keep it airborne, that inspired him to eventually build his own solar plane, the Sunseeker. His experiences with both of these early airplanes equipped him with the necessary skills and insight to build a plane that could fly cross-country, west-to-east. He points out that Solar Challenger was the first machine to run entirely off of its photovoltaic cells, instead of its batteries. However, it could only fly heading north during the noon hour because it had to keep sunlight falling on its large, broad wing or risk losing power. Still, it proved it could be done.
"My design was a complete departure from anything that had been done previously," Raymond explained to me. "I made a very small wing, which could only generate enough power for level flight. The idea was to take-off on battery power, then to transition to thermal lift or on continuous, sustained mode on photovoltaics."
His efforts attracted the support of Sanyo, who provided him with experimental, amorphous, thin-film solar cells, which in 1990 were only about two percent efficient at converting sunlight into electric power. It wasn't as much as Raymond would have liked, because it would require more surface area on the parasol wing he was envisioning, but in his words, Sanyo's "publicity machine was cranked up." This compelled the Californian to keep his sailplane idea moving forward although he had to give up on managing sustained flight on sunlight. Instead, he'd take off on battery power and soar until the PV panels built into his long, thin, parasol wings could recharge his NiCad batteries.
Since his 1990 transcontinental flight -- which still remains the record -- Raymond has built a new wing that incorporates monocrystalline silicon cells efficient enough to generate 1,800 watts of energy. He noted that he only needs about 1,100 watts to maintain sustained flight in Sunseeker.
Flying on solar power across North America was not Raymond's first objective; he had much grander plans in mind: a solar flight around the world, but the technology just wasn't available a decade and a half ago. When he isn't hang gliding or dreaming of world-girdling solar sailplane epics, Raymond works at Aerovironment, Dr. Paul McCready's R&D firm; they're the folks who built the first human-powered plane to cross the English Channel and the prototype of the EV1 electric car. Raymond tells me that his colleagues now think an around-the-world flight is now possible... barely.
It's the "barely" part that I think intrigues Raymond the most, but he now has competition in the form of the Solar Impulse team in France who have a large, two-place machine on the CAD system. What Raymond needs to beat them is some deep-pocket sponsors, but in the interim, he is working on perfecting a solar wing skin system that can be seamlessly integrates the photovoltaic cells into a super-smooth, laminar airfoil.
Thoroughly Modern Icarus
Sunseeker is constructed out of ultra-light, carbon-fiber bonded with high-temperature resins, unlike most other carbon-fiber, "plastic" sport planes built today, which use low-temperature resins. While the later is easier to work with and lets hobbyists build high-performance, sophisticated aircraft, it is unsuspecting to heat, in large part because the carbon fiber framework is jet black and can get very hot in the sun, causing low temperature resins to soften and delaminate with potentially catastrophic consequences. Raymond explained to me this is why carbon fiber sport planes are almost invariably painted white, in order to keep down the temperature of the underlying material.
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