After four years of research, studies, calculations and simulations, the
Solar Impulse project has entered a concrete phase with the construction of an initial
prototype with a 61-metre wingspan, referred to by its registration number
“HB-SIA”. Its mission is to verify the working hypotheses in practice and to validate
the selected construction technologies and procedures. If the results are conclusive,
it could make a 36-hour flight – the equivalent of a complete day-night-day cycle -
in 2009 without any fuel.
TWO AIRPLANES ON THE WAY TO SUCCESS
Construction of the first prototype, the HB-SIA, began in June 2007 and will last until the summer of 2008. Test flights should start in autumn 2008, with the objective of completing the first night flight in 2009. Another plane will then be developed to
attempt to fly several 24-hour cycles consecutively, leading to the first trans-Atlantic
flight in 2011, and then the first round-the-world flight.
HB–SIA’S MISSION
This is a “basic” prototype airplane. The instrument panel will be reduced to the
essentials, and with a non-pressurized cockpit it will be unable to fly above 8,500 m.
It will be a first approach at optimizing the balance between energy consumption,
weight, performance and controllability. The goal is not to try to fly around the world
and indeed the HB-SIA is not built to do so.
The objectives at this stage are:
• To validate the computer simulation results, the technological choices and the
construction techniques.
• To test an unexplored area of flight: never before has an airplane succeeded in
flying with these size, weight and speed characteristics.
• To store sufficient solar energy during the daytime to demonstrate the feasibility
of a day-night-day cycle (36-hour flight).
EXAMPLE OF ENERGY EFFICIENCY
Current solar airplanes are not designed to store energy and therefore have to land
in cases of insufficient sunlight (clouds or night time). In so doing they mark the
limits of solar energy. Other projects are seeking to fly remote controlled solar
drones or hydrogen-powered airplanes. To demonstrate the formidable potential of
renewable energies, Solar Impulse intends to place the bar much higher and have
a piloted aircraft fly night and day without fuel.
But how do we succeed with a mission like this, when we know that with present-day
technologies and performances, every square metre of photovoltaic cells can supply
only 28 watts – the equivalent of an electric light bulb – to the propeller continuously
over a 24-hour period? In other words, how can an airplane fly on the energy consum -
ed by a supermarket window? It is impossible without a complete optimization of the
airplane and without a drastic reduction in its energy consumption.
Only a machine of disproportionate dimensions (61 metre wingspan) and very light
weight (1500 kg) will be able to fly sufficiently slowly (45 km/h) to operate off the
available energy! The Solar Impulse engineers have therefore had to develop a
totally new type of airplane, made possible by innovative technologies, in which every -
thing is new, everything is different: aerodynamics, structure, manufacturing methods, type of propulsion, flight domain…
In some ways it looks like a large aircraft, in others more like a glider. It has the
wingspan of the Airbus A340 and the wing load of paragliders and delta planes. In
relation to its size, it must be eight times lighter than that of the best existing glider.
This poses the problems of:
• constructing a structure with this wingspan and such a low weight;
• finding the balance between stability and manoeuvrability, in other words how to
make an airplane of this size and with such a low wing load pilotable?
MODEL OF HIGH TECHNOLOGY
The project will be successful only if it can achieve performances which are still
unknown today, achieved by a combination of practical experimentation and complex
computer simulations.
To achieve this, a multi-disciplinary team of 50 specialists from six countries, based
in Dübendorf and Lausanne, assisted by a further roughly 100 outside advisers, are
pooling their very specific experiences to create the necessary synergies. It is only
by combining the demands of the designers, equipment suppliers, constructors and
pilots that an airplane can be built to such atypical specifications. Research initiatives
have had to be undertaken and new solutions called into play in a number of
sectors – conception, aerodynamics, energy efficiency, structure, composite materials
and manufacturing procedures – both for each component individually and for
the assembly as a whole.
An elegant example is the extreme precision achieved in the use of composite
materials: for example stretching carbon sheet just a few tenths of millimetres thick
over lengths of up to 20 metres. As the Project CEO, André Borschberg, says,
“Anything that doesn’t break is potentially too heavy!”
The fragile solar panels also had to be flexible in flight. How do we use cells as both
energy generators and wing surface, without breaking when the airplane encounters
turbulence?
Of course, all this represents the management challenge of bringing together
individualists who are as bold as they are creative, getting them to work as a team
and motivating suppliers to move beyond their customary limits.
SYMBOL FOR OUR SOCIETY
For Bertrand Piccard, the initiator and president of the project, this airplane is the
symbol of the new technologies that our society ought to be capable of rallying
behind it in order to economize the energy resources of our planet.
Solar Impulse, in this sense, really means what its name says. The sun provides the
energy, but the impulse to use it has to be transmitted to people who are ready to
receive it and carry it further.
In any case, it demonstrates the importance of tomorrow’s adventures being linked
to the search for a better quality of life.
HB-SIA Press Conference Video: CLICK HERE
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