- Charlotte Pichon
Solar Impulse SA – www.solarimpulse.com
Inventing The Future: Flying Without Fuel
For the first time in history, an airplane has succeeded in flying night and day without any fuel, powered for 26 hours by nothing but solar energy. This flight, on 8 July 2010, brought the initial phase of the Solar Impulse adventure launched by Bertrand Piccard and André Borschberg to a successful conclusion, validating their goal of demonstrating the enormous potential of new technologies for saving energy and applying renewable forms of energy.
In its quest for the ultimate in technological performance and symbolic force, Solar Impulse has set out on the precarious and risk-strewn path trodden by all pioneers. Since 2003, a team of creative mechanical and electrical engineers, physicists, IT experts, and composite material specialists have applied all their skills to build this revolutionary aircraft, capable of coming close to perpetual flight.
Solar Impulse believes in the power of symbols. By writing new pages of aviation history with solar energy, including even a round-the-world flight with no fuel or polluting emissions, Solar Impulse is demonstrating the enormous potential of new technologies for energy saving and the production of renewable energies. This Solar Impulse initiative is both scientific and innovative. It is also philosophical, by virtue of its concern to heighten awareness in society of the need to be sparing with our planet’s energy resources.
To produce an aircraft that will take off and fly autonomously both day and night, propelled only by solar energy, is a tremendous challenge that required the optimization of new kinds of technology and a drastic reduction in energy consumption. Solar Impulse’s 70 engineers and technicians, supported by a hundred or so experts and advisers, have had to apply highly innovative aeronautical solutions. Whilst not the first solar aircraft project, Solar Impulse is certainly the most ambitious. With its successful flight through night and day, the HB-SIA prototype became the first aircraft to come close to perpetual flight.
With the giant wingspan of an Airbus A340 and a miniscule weight, that of an average car, the HB-SIA prototype presents constructional and aerodynamic features never before encountered. Carbon fibre structure, propulsion chain, flight envelope and instrumentation, ever ything has been rethought and designed to save energy, resist high altitude factors hostile to both materials and pilot, and to combine the constraints of weight with the need for strength.
Structure and Materials: Attaining a wingspan in excess of 63 m with a weight of only 1,600 kg represents a major first in the world of aviation, as regards robustness, lightness and manoeuvrability. Solar Impulse is built of composite materials, consisting of a carbon fibre-honeycomb sandwich structure. The upper wing surface is covered with a skin of embedded solar cells, and the undersides of the wings with a high-resistance flexible film. 120 carbon-fibre ribs placed at 50 cm intervals give the wing its aerodynamic profile as well as ensuring its rigidity.
Energy Capture and Storage: To succeed, the project must maximize aerodynamic performance and optimize the energy chain. The 11,628 monocrystalline silicon cells covering the wing and horizontal stabilizer, each 150 microns thick, were selected for their lightness, flexibility and output (22%). Their energy efficiency could have been higher still, but the additional weight would have penalized the aircraft during night flight. This being the most critical phase of flight, the major constraint in the project is storing enough energy in the lithium polymer batteries, whose energy density is 240 Wh/kg. Situated in the four engine nacelles, these batteries weigh in total 400 kg, a quarter of the total weight of the aircraft.
Energy Resources: At midday, each m² of land surface receives the equivalent of 1,000 watts, or 1,3 horsepower of light power. But over 24 hours this averages out at just 250 W/m². With 200 m² of photovoltaic cells and 12 % total efficiency of the propulsion chain, HB-SIA’s four engines achieve on average only 8 HP or 6 KW – roughly the amount of power the Wright brothers had available to them in 1903 when they made their first powered flight. And it is with this energy, optimized from the solar panel to the propeller by the efforts of an entire team, that Solar Impulse managed to fly day and night without fuel!
Tests and Virtual Flights: Calculations, tests and simulations are an integral part of each project phase. During construction, wing-loading and vibration tests allowed the engineers to fine-tune their models and then move forward step by step into totally unknown territory. In preparation for the first flight tests, a simulator was specially developed to train the pilots to operate in the tiny 1,3 cm3 cockpit, and control an aircraft whose large span and low wing-loading result in tricky handling characteristics. The multi-disciplinary mission team simulated countless flights, in search of the most suitable weather patterns, to secure access for the solar aircraft to controlled airspace, and to prepare for landings at international airports.
Propulsion System: Fitted beneath the wings of HB-SIA are four nacelles, each containing a 10 HP motor, a lithium polymer battery set and a management system controlling charge / discharge and temperature. The thermal insulation has been designed to conserve the heat radiated by the batteries and so keep them functioning despite the -40°C encountered at 8,500 meters. Each engine is fitted with a reduction gear that restricts each 3,5 meters diameter, twin-bladed propeller to an RPM in the range of 200-400.
- Wingspan: 63,40 m
- Length: 21,85 m
- Height: 6,40 m
- Weight: 1600 kg
- Power source 4 x 10 HP electric engines
- Solar cells: 11628 (10748 on the wing, 880 on the horizontal stabilizer)
- Average flying speed: 70 km/h
- Take-off speed: 44 km/h Stalling speed: 35 km/h
- Maximum cruising altitude: 8500 m (27900 ft)
First DAY/NIGHT Solar Fight in History
The wingspan of an Airbus A340, in order to minimize induced drag and offer maximum possible surface area for the solar cells
The weight of a family car – every unnecessary gram has been eliminated in order to build a super-light aircraft
The average power of a scooter, after optimizing to the extreme the entire energy chain
Seven years of calculation, simulation, construction and testing
A multidisciplinary team with 70 specialists, 80 partners and about a hundred advisers
3 World Records in the solar-powered aircraft category:
- Duration (26 h, 10 min, 19 sec)
- Absolute altitude (9235 m, 30300 ft)
- Gain of height (8744 m, 28688 ft)
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