September 13th, 2017
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!!!
