|A rendering of the HB-SIA prototype above a commercial A340 to show comparison of wingspan and scale. Click to enlarge.|
The Solar Impulse HB-SIA prototype electric aircraft made its first flight on 7 April. The goal of the Solar Impulse Project is to develop a solar airplane that can take off and fly, day and night, powered by solar energy alone around the world. In the flight, the Solar Impulse HB-SIA prototype climbed up to 1,200 meters, then flew for 87 minutes with test pilot Markus Scherdel at the controls.
A total of 11,628 monocrystalline silicon cells (10,748 on the upper wing surface, 880 on the horizontal stabilizer), each 150 microns thick, run four 7.5 kW (10 hp) electric motors and store the solar energy for the night in a 400 kg lithium-ion polymer battery system (25% of the weight of the plane). Each motor is mounted in a gondola beneath the wing which also contains a lithium polymer battery set and a management system controlling charge/discharge and temperature.
|“This first flight was for me a very intense moment. The HB-SIA behaved just as the flight simulator told us. Despite its immense size and feather weight, the aircraft’s controllability matches our expectations.”|
Thermal insulation conserves the heat radiated by the batteries and keeps them functioning despite the -40°C encountered at 8,500 meters. Each engine is fitted with a reducer that limits the rotation of each 3.5 meter diameter, twin-bladed propeller within the range of 200-4,000 rpm.
The prototype airplane has the wingspan of a large airliner (63.40 meters) and the weight of a midsize car (1,600 kilograms). With 200 m² of photovoltaic cells and 12% total efficiency of the propulsion chain, the aircraft’s motors achieve on average just 6 kW (8 hp)—roughly the amount of power the Wright brothers had available to them in 1903 when they made their first powered flight.
Solar Impulse is built round a carbon fibre-honeycomb composite using a sandwich structure. The upper wing surface is covered with a skin of encapsulated solar cells, and the undersides of the wings with a high resistance flexible film. 120 carbon fibre ribs placed at 50 cm intervals profile these two layers and give the body its aerodynamic shape.
Average flying speed is 70 km/h (38 mph); take-off speed is 35 km/h (19 mph).
Solar Impulse is supported by, among others, the Solvay group, Omega, and Deutsche Bank, who are its Main Partners. Bayer MaterialScience and Altran are the project’s Official Partners. The Ecole Polytechnique Fédérale de Lausanne (EPFL) is the Official Scientific Partner and Dassault-Aviation is the aircraft design and production Consultant.