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How to conceive a solar airplane

This is the first of a series of articles about the construction of Solar Impulse’s second generation aircraft, HB-SIB, providing a step-by-step “behind the scenes” presentation. More specifically, I will introduce the different teams involved in the project. I will start from the first step necessary for the development of a solar airplane: the concept. Why does HB-SIA look the way it does? And how will its big brother look like? These questions, although seemingly simple, required careful research and analysis.

I had a chat with Peter Frei, Head of Conceptual Design and Aerodynamics at Solar Impulse. A friend of André’s from their days in the Swiss Air Force, Peter Frei has been on the project from the start. He participated in the first meetings at the Federal Polytechnic University in Lausanne (EPFL) where simulations and calculations confirmed that HB-SIA would have to be an airplane and not in airship in order to fly with solar energy alone. 

Designing an airplane is a multidisciplinary process. It starts from a set of specifications given by the person with the idea and objectives. Bertrand wanted to fly around the world solely on solar energy. To achieve this, the engineers already had an indication about the power source, the flight specifications (to fly across Oceans, for example) and the minimum weight requirements such as: a manned solar aircraft able to fly at night, with batteries capable of storing energy, with provisions for the pilot, and so on. The general concept trigged Peter’s curiosity, convincing him to use his extensive engineering experience to find solutions for these strict requirements. Curiosity and creativity, as well as team work, are the key ingredients for designing an initial concept. Ideas must be challenged and the only way to find lighter, cheaper and more efficient solutions is to engage in critical thought with others.

Jotting down the first concept for a solar aircraft is a long process and many people need to be involved. For HB-SIB this process took over a year while for HB-SIA it took even longer because it was the first of its kind. Three dimensional sketches and simple hand calculations are the tools these skillful men start with to adequately develop ideas for further discussion in an engineering team.

Peter was always fascinated by airplanes. Even as a child he used to build models. It’s the physics behind flight vehicles that intrigue him and one of the main reasons why working to develop the world’s first solar aircraft to fly day and night was an inspiring feat. Him and one of his former students, Roger Ruppert had to decide how far they dared to extrapolate their experience with ultra-light materials and how large of a wing span they were prepared to handle in reality, conscious that they had to go beyond  the size of existing airplanes.

Although HB-SIA and HB-SIB will visibly be from the same family, they remain fundamentally different. The new airplane is an optimized and more complex version of its older brother. It will be larger (by 11%), it will be able to carry more weight, it will be more resistant to humid climates and, most importantly, the pilot will be much more comfortable during some of the longer legs, which could last up to several days. But you will discover these differences in the upcoming series, so stay tuned!

Follow the series here: “THE MAKING OF A SOLAR AIRPLANE”

This is the first of a series of articles about the construction of Solar Impulse’s second generation aircraft, HB-SIB, providing a step-by-step “behind the scenes” presentation. More specifically, I will introduce the different teams involved in the project. I will start from the first step necessary for the development ...



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