A Sample Feature From Aviation News

Flying on Impulse – and the power of the sun

Switzerland is famous for several unique products. It has some of the most distinctive cheeses money can buy, the most expensive and near perfect watches that few can afford, trains that always arrive on time, and surprisingly successful industries – Pilatus and Oerlikon to name but two. Soon there will be something else unique to Switzerland – the first solar-powered aircraft designed fly around the world, landing only five times as it circumnavigates the earth.

Above: Capable of accommodating a lone pilot in a tightly fitting nacelle fabricated from composite materials, the HB-SIA will serve as a much needed precursor to a round-the-world flight planned for 2012. (All photos, Solar Impulse)

In 1999 Bertrand Piccard and fellow pilot Brian Jones entered the record books with one of the last great aeronautical achievements of the 20th century. In a sustained flight lasting 19-days 21hr 47min, they flew the Breitling Orbiter 3 balloon from the Chateau d’Oex in Switzerland around the world, landing again in Egypt. However, one aspect of the flight troubled Piccard. It rankled him that in achieving this he had consumed more than four tons of propane gas and released that amount of toxic pollution back into the atmosphere. Bertrand Piccard is no born-again environmentalist hitching to a popular bandwagon. He comes from a family who have spent three generations exploring the earth and celebrating the diversity of its burgeoning life forms.
His grandfather, August Piccard, was an inventor, balloonist and explorer, joined in that activity by his father Jacques who brought the genre of the nature documentary to a generation of TV viewers long before David Attenborough first appeared on the small screen. Through his stunning films of the world’s seas and oceans, he inspired a generation of explorers to see the world not as an earth but as a water planet. Now it’s Bertrand’s turn.

Below: The sheer size of the lightweight, powered glider is only fully appreciated when scaled against an Airbus A330/340 series airliner, it’s high aspect ratio wing providing a high lift to drag ratio.
Pic 3

Along with a select group of sponsors and associates, he wants to fly around the world in an aircraft called Solar Impulse, powered by electricity, without burning one gram of hydrocarbon fuel to stimulate thinking about how we can fly clean aeroplanes. Piccard simply wants to turn aviation on its head and fly without engines and without fuel, and to do so over great distances. This is not a new idea. People have been trying for more than 20 years to harness the power of the sun, driving electric engines through accumulators and batteries. What Piccard wants to do is something different, to send a message to people everywhere, that it is possible, through invention, innovation and creative engineering, to stimulate new ways of propelling aircraft in a completely clean and toxin-free manner. As a renaissance man, it matters to Bertrand Piccard that his vision for a future world embraces all conceivable technologies and the widest range of innovative solutions. While some choose to appease their guilt at the use of dirty engines by campaigning for the demise of the aeroplane, Piccard chooses to develop solutions, and some of his stimulating concepts are encouraging enough for industry, bankers and investors to get involved. Piccard does not expect Solar Impulse to be the way to replace hydrocarbon engines (reciprocating or reactionary). His project is designed to get people thinking outside the box and it does that very well.

Like all good ideas, the fundamental purpose of Solar Impulse is easy to grasp. It aims to produce an aircraft that can take-off and fly autonomously, day and night, travelling around the world without using fuel and without emitting any pollution. It is a simple idea, only the means being a goal at the edge of technical reach. Powered solely by light from the sun falling on photovoltaic cells attached to the upper surface of the wings, Solar Impulse will gather energy for its lithium batteries during only eight hours each day. Only when the sun is more or less directly overhead can the cells convert light into electricity and charge batteries essential for keeping the propellers turning during hours of darkness. At low incident angles of sunlight there is insufficient energy falling on the cells to provide power. For only one-third of each 24 hours can Solar Impulse gather its ‘fuel’, pure sunlight, to drive its four specially designed propellers.

Above: The large number of solar cells comprising an integral structural part of the upper wing surface creates a major thermal problem in itself, a degree of heat associated with the light-soak essential for converting sunlight into electrical energy.

Above: There is as much technology in the design of the highly efficient propellers as in the main structure of Solar Impulse, the relatively slow rotation rates anticipated made possible only through unusually effective wash-to-force rations.

For the rest of this feature please see the 2008 issue.