Solar Impulse

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Solar Impulse

THE CHALLENGE

The Solar Impulse project aims to have a plane powered exclusively by solar energy take off and fly autonomously, day and night, to the point where it could circumnavigate the globe with no fuel, generating no pollution.

The pilots of the Solar Impulse, Bertrand Piccard, psychiatrist/adventurer, and André Borschberg, pilot/entrepreneur, have been leading the project since 2003. Beginning with the first flights, they will share the missions, as at the moment the aircraft can only carry one pilot at a time.

THE MAJOR STEPS

This is a long-term project:

• Feasibility study at the Ecole Polytechnique de Lausanne in 2003.

• Development of the concept in 2004-2005.

• Simulation of long-haul flights as of 2006.

• Design and manufacture of a prototype in 2006-2007.

• Test flights and first night flight with the prototype in 2008-2009.

• Construction of the final plane in 2009-2010.

• Missions of several days, crossing the Atlantic and trials circumnavigating the globe with five stages in 2011.

The aim of the project is to fly around the world. Take-off should occur in May 2011, for a flight around the world near the equator, but essentially in the northern hemisphere. Five stops are planned to change pilots and update the public and political and scientific authorities on the adventure. Each leg will last three to four days, which is the maximum time one pilot alone can handle. Once the efficiency of the batteries makes it possible to reduce the weight, the aircraft could carry two pilots for long flights, and a trip around the world without stopping will be possible.

AERODYNAMIC

The wingspan of the aircraft measures 80 metres, slightly wider than the wingspan of an Airbus A380, in order to minimise drag and offer a maximum surface for solar cells. Such light wing loading (8 kg/m2) creates greater sensitivity to turbulence. The ultra-light structure must use customised carbon fibres.

Max. altitude	12,000 m
Max. weight	2000 kg
Average speed	70 km/h
Wingspan	80 m
Max. power of motors	35 kW
Battery weight	450 kg
Battery capacity	200 Wh/kg
Photovoltaic efficiency	0.2

MATERIALS AND STRUCTURE

While traditional sandwich composites have an area density in the order of 10 kg/m², those developed for the Solar Impulse should weigh in the order of 0.5 kg/m². These materials could also have functionality integrated, such as integrity sensors, active control of the form, etc.

A “skin” of ultra-thin solar cells will be integrated to the wings. These cells will be flexible to conform to changes in shape and vibrations and should be encapsulated to guarantee maximum efficiency in all conditions, optimal resistance to exterior aggressions, and make a structural contribution.

ENERGY

There is an additional difficulty in that the energy captured during the day will serve both to propel the plane and to recharge the batteries to be able to fly at night. The pilot will therefore need to have full batteries every night and to save as much energy as possible to stay in the air until the following sunrise. Energy is accumulated during the day in lithium batteries in the wings, the density of which must be close to 200 Wh/kg, in spite of temperatures ranging from +80 C to –60 C.

PROPULSION

The average power over 24 hours available to the motors from the sun in practically equal (12 CV) to what the Wright brothers had in 1903 when they made the first flight in history. The success of the project will depend upon optimising performance and reducing overall weight.

THE COCKPIT

Because of the weight of the batteries, the cockpit will only be able to hold one pilot, who must be able to fly at an altitude of up to 12,000 metres, in extreme conditions in terms of pressure and temperature. The cockpit will therefore be equipped with a variety of systems: pressurisation, oxygen distributions, elimination of CO2 and humidity generated by the human body. These devices will also need to be extremely light and consume little energy so as to take nothing away from the propulsion.

The project has several Partners such as:

Main Partner: Solvay and Omega

Official Partner: Altran

Scientific and Aeronautical Partner: the EPFL, the European Space Agency (ESA) and Dassault