André Noth won the 2010 Jakob Ackeret Price / Presentation on 11th June 2010

Dr. André Noth, dipl. Ing. EPFL, Debiotech SA, Lausanne:

Design of Solar Powered Airplanes for Continuous Flight

Abstract
The thesis of André Noth deals with airplanes using solar energy as their only source of energy for more than 24 hours flight. Using solar panels, they collect it during the day for immediate use but also store the remaining part for the night flight. This work presents a new analytical methodology for the conceptual design of such airplane. Its major advantage lies in the fact that it is simple and versatile, which makes it applicable to a large range of airplanes of different wingspans, from the small MAV to the large manned aircraft. The design methodology is based on power and mass balances occurring during level flight. An extensive study was done on the mathematical modeling of the subparts, for example concerning electric motors
the question being to know how their mass and their efficiency vary with power. Empirical data over a large range were used in this study. Finally, the analytical method contains 5 mission parameters and 25 others linked to the various technologies involved that the user can vary in order to see on a graph the dependencies between the 3 layout variables (aspect ratio, wingspan and total mass) for all the feasible solutions. The final selection can then be easily made.
Sky-Sailor, a 3.2 meters wingspan solar powered airplane, was then designed using this methodology.
A prototype, with an ultra lightweight structure covered by silicon solar cells was
built in order to validate the process. We also developed in this framework dedicated electronics for the autonomous navigation and the efficient solar power management. The final 2.44 kg airplane was tested with success during several autonomous flights, showing capabilities that were very close to the one calculated in theory. The longest flight achieved lasted more than 27 hours within a circuit length of more than 874 kilometers and proved the feasibility of solar powered continuous flight.
In addition to the first application example on Sky-Sailor, other designs are presented and  discussed, like the case of a 70 cm solar UAV but also a 60m manned solar airplane. It is then very interesting to see how things evolve with scaling. In fact, going in each direction removes and adds its batch of new problems: the poor efficiencies of aerodynamics and propulsion group prove very unfavorable when down-scaling whereas the weight and fragility of the enormous wing structure become the nightmare of engineers working on large-sized models.
Finally, various additional possibilities to improve or enhance the endurance of a solar airplane are addressed, such as gaining altitude to store energy, taking benefit of ascending thermal winds or using a swiveling solar tracker.

Invitation (pdf, 100kB)