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How to prepare the flights around the world

The aircraft was imagined, dreamt of, then designed, developed, built and tested. The preparatory missions then followed one after the other, each one with increasing difficulty. Now we have succeeded in building that aircraft, a solar aircraft. However it is still merely the equipment to fly around the world. We are currently up against the wall. Indeed, the team needs very much more to succeed in the flight around the world. It requires lengthy preparation at each stage. Even if the aircraft is energy self-sufficient, it is not so on the ground. A team will be required to follow it across continents and oceans, in order to prepare take-offs and landings. We are combining all our expertise together so that Solar Impulse can achieve this outstanding feat! Christian Le Liepvre, in charge of the Solar Impulse partnership at Altran, January 2015

What are the challenges to be taken up?


The main constraint of Solar Impulse is the weather. Around the world, it has to cross mountain ranges, deserts and also oceans for the very first time. It is therefore necessary to take into account these factors to determine the best flight path, and avoid clouds, rain and turbulence. 

The plane needs sun: Solar Impulse captures its energy in the daytime to reach higher altitude and to recharge batteries. When night falls, it descends gliding from 9,000 to 3,000 metres and the batteries then take over. Another challenge for Solar Impulse is its own weight. Indeed, the aircraft must be as light as possible to consume as little energy as possible. To achieve it, even the quantity of resin to make the joints between the structure plates was reduced! As a consequence, engineers had to find the right balance between weight and performance of the plane.

 In addition, the Mission Control Center team has to monitor the stages of the flight, which last up to five consecutive days. During this time, the Si2 has to cross several different air traffic control areas and has to get flight clearances in real time.

 Lastly, the huge challenge for the pilot is to be alone on board for several days – even if he can rely on the virtual co-pilot, which alerts him via a buzzer on his arm when it detects anomalies.



What solutions is Altran bringing?

As one of the very first partners of the project, the Altran group is involved to a higher degree, alongside the Solar Impulse team. During the ultimate stages of this project, Altran presence will be particularly important and at the very heart of the mission, putting all its expertise into making this venture successful. Our experts are playing a decisive role.

Altran engineers designed a system which acts like a real-life co-pilot, assisting the pilot on board so that he can rest or focus on other tasks.

André Borschberg on board HB-SIA

The SAS (Stabilisation Augmentation System) is a basic autopilot which maintains the aircraft’s altitude and trajectory. The MAS (Monitoring and Alerting System) is new equipment, designed on high reliability methodology. It compares the trajectory requested by the SAS to the actual trajectory of the aircraft. If deviation is detected by the MAS, it alerts the pilot to take control of the aircraft, using a vibration alarm strapped to his arm.

Altran is also responsible for analysing the security in view of the requirements the aircraft has to meet to obtain flight certifications and authorizations. Since no other aircraft of this type has ever existed, traditional methods of analysis must be adapted to the singular case of Solar Impulse. This task naturally calls on Altran expertise. Our engineers are also busy analysing and improving the design of the oxygen system used by the pilot to breathe during flight.

The most crucial contribution of Altran to Solar Impulse is surely its expertise in modelling and simulation carried out by our consultants. During actual flight, the team simulates all possible flight paths in order to take the most suitable decisions. Because of weather variations, the aircraft is never exactly where it is expected; the team and the Altran consultants must therefore also optimise real time calculations to consume the least possible energy and to optimise the flight path. In the long run, the Altran team must anticipate and simulate trajectories and potential stops to find those which are the most favourable.

Altran control screen in the MCC

See how Altran guides Solar Impulse around the world

Altran team

Altran experts focus

Christophe Béesau, Altran Project Director, Advanced Modelling and Simulation, for Solar Impulse
Christophe Béesau, Altran Project Director, Advanced Modelling and Simulation, for Solar Impulse

Solar Impulse 2

Watch the assembly of the round-the-world aircraft!