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Interview of Mr. Hannes Ross, Design Advisor and Consultant for the Swiss Project Solar Impulse

Mr. Hannes Ross, Design Advisor and Consultant for the Swiss Project Solar Impulse, will be one of the eleven distinguished personalities of the Aeronautics Community which will give a Key-Note Lecture in the frame of the 7th EASN International Conference. In his interview he narrates the success story of traveling aroung the world with a Solar Powered Aircraft.

Q1: What has been the motivation for building the Solarimpulse aircraft?

The idea to develop a solar powered aircraft was born by the Swiss entrepreneur Bertrand Piccard, after he and his British copilot Brian Jones flew around the world in a hot air balloon in 1999.
After the landing the balloon in Egypt he became fully aware, that from the initial liquid gas quantity of 4.3t only 35kg were left, i.e. less than 1%.  Looking back at the whole mission he realized that a lot of problems could have resulted from a shortage of fuel enroute.  He then started to dream about an aircraft with a propulsion system with unlimited energy resources.

Q2: What is its Mission?

Just having successfully finished the circumvention of the earth, Bertrand Piccard thought about how much easier it would be to fly around the world using Solar Power. And this idea became the seed for promoting the Solar Impulse program with the motto: "Fly around the world with Solar Power and without using a single drop of fossile fuel".

Q3: Which are the main advantages of such an aircraft? 

This type of aircraft with "unlimited" energy resources would allow to fly around the world and control the flight path and altitude much better than "drifting" around the world in a balloon. And besides it would demonstrate what can be done using solar power.

Q4: Which have been the challenges in designing and building it? 

Manned and Unmanned solar powered aircraft have been designed an flown since the mid 1970. But none of those aircraft was designed to fly more than 24 hours and - even more important -  for a couple of days by a single pilot to allow crossing the Pacific or the Atlantic. There was no big company (like Airbus, Boeing etc.) nor any small company willing and capable to design, develop and test this kind of vehicle. Therefore a new company had to be formed, a design team had to be assembled and - equally important -  sponsors had to be found to provide funding and technical support for the program. 
A careful balance between (wing) size, power required, battery size and overall mass had to be found to meet mission requirements.
No design or performance criteria nor equipment (solar cells, batteries, engines etc) where off the shelf available to be used for the design/development process. The aircraft would have to be extremely light (in all components) from structure to equipment to come up with a reasonable solution. A lot of new carbon fibre materials / components had to be developed. Engineers for all disciplines had to be found, convinced of the idea, to start the program. A good mix of experienced older / retired engineers and younger, eager, dedicated engineers with good knowledge of modern digital tools were assembled, collocated in D?bendorf, Switzerland. And official Government agencies had to get involved to define and conduct a certification process. 
It turned out, that to just develop the aircraft and fly it around the world was too risky a process. A stepwise approach was therefore selected and a Demonstrator was built to verify the design assumptions and show, that a solar aircraft could fly throught the night for more than 24 hours and could continue for several days. That was demonstrated in 2010. Thereafter the decision was made, to design, develop, test and certify the aircraft, which would be used to fly around the world. That aircraft - Solarimpulse 2 - first flew in the summer of 2014.
It is to be noted, that during the development - which actually started with a feasibility study in 2003 - improvements did happen in the technical characteristics of materials, equipment, solar cells, batteries etc.
However it must be understood, that the physical boundaries of solar power in providing energy are very tight. Outside the atmosphere the energy which can be collected by one m² of solar cells is about 1300W. Considering all the efficiencies from the solar cell within the earth atmosphere over batteries, engines including propellers the energy available is very small and will not allow to use this kind of an aircraft for commercial applications with a performance level of todays airliners. 
However, even today the utilization of electrical propulsion systems for sport / utility aircraft with reasonable endurance and speed has started.

Q5: Challenges of the Round the World Flight Mission?

The financial resources must allow design, development, manufacturing, testing and mission flights!!!

  • Technical: The aircraft and all systems have to function continuously for up to 7 days.
  • Weather Prediction: Forecast has to allow the intended mission routing and altitude profile.
  • Pilot Endurance: The single pilot has to to be able to control the aircraft throughout the mission, i.e. for up to 7 days. 
  • Communication: Communication with the Mission Montrol Center must be maintained

Q6: Could you please indicate the significance of this aircraft for the environment?

The Solar Impulse aircraft concept has demonstrated, that long distance flights (>7000 km, with a 5 day duration, flown by a single pilot) can be achieved without a single drop of fossile fuel. The big aircraft companies (Airbus/Boeing and the manufacturers of (electric) engines), all have started the development of hybrid or all -electric aircraft - similar like the development of electric cars. If we consider the climate change and the current pollution of the atmosphere, we have to continue to use new and sustainable energy source to provide mobility for people and transport capability for the future without polluting our planet. It will take some time to get there, but then Ott Lilienthal flew in 1896 and the first powered flight happened in 1903.
Solar power is currently the only reliable source available for the future for mankind. We have to learn to collect it more efficiently and in particular to store it. Nuclear fusion is still too far away to judge its availability and the risks involved.

Q7: What is the message you would like to provide to the readers of the EASN Newsletter? 
The Solarimpulse program demonstrated, that available technologies not only allow to start new roads to reduce energy consumption, but clean energies can be used today to satisfy the needs of the worlds population, thereby providing a clean environment for the generations to come.
Let us go and do it!!!

Date posted: September 13, 2017, 11:57 am

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