Design of Solar Powered Airplanes for Continuous Flight December 2006 3 Application of the methodology Having the mission requirements, the method explained here above can be applied in order to evaluate the possible shapes of a solar airplane. This will be illustrated with the example of the Sky-Sailor prototype. The objective here is to embed a 250 g payload consuming 0.5 W and fly continuously at low altitude during two months in summer. These mission parameters allow plotting the relations between the main variables, i.e. wingspan and aspect ratio, and the flight characteristics for all the possible configurations. Fig. 8. Design plots of a solar airplane with a payload of 250 g This is done on Fig. 8 where one can first observe that the minimum airplane wingspan is around 2.5 m and that keeping the same construction quality the airframe will become too heavy from a certain point and make continuous flight impossible. This means that for larger airplanes, the quality of the wing structure in terms of weight becomes more and more important. In the range of ten to twenty meters wingspan, which corresponds to commercial sailplanes, the construction method used today should be massively improved to see one day a model in this range fly continuously. In our case, among the many possible configurations, the final choice will be guided by considerations on the flight size or even production costs that can be estimated knowing the prices of the different elements. It is also interesting to have a look on mass distribution. Fig 9 shows that the half of the weight is only due to the battery and that the structure constitutes also an important part that increases with wingspan as said before. This knowledge allows putting efforts on the critical instead of working on elements that play a minor role in overall mass. André Noth and Roland Siegwart 13
Design of Solar Powered Airplanes for Continuous Flight December 2006 3 Application of the methodology Having the mission requirements, the method explained here above can be applied in order to evaluate the possible shapes of a solar airplane. This will be illustrated with the example of the Sky-Sailor prototype. The objective here is to embed a 250 g payload consuming 0.5 W and fly continuously at low altitude during two months in summer. These mission parameters allow plotting the relations between the main variables, i.e. wingspan and aspect ratio, and the flight characteristics for all the possible configurations. Fig. 8. Design plots of a solar airplane with a payload of 250 g This is done on Fig. 8 where one can first observe that the minimum airplane wingspan is around 2.5 m and that keeping the same construction quality the airframe will become too heavy from a certain point and make continuous flight impossible. This means that for larger airplanes, the quality of the wing structure in terms of weight becomes more and more important. In the range of ten to twenty meters wingspan, which corresponds to commercial sailplanes, the construction method used today should be massively improved to see one day a model in this range fly continuously. In our case, among the many possible configurations, the final choice will be guided by considerations on the flight size or even production costs that can be estimated knowing the prices of the different elements. It is also interesting to have a look on mass distribution. Fig 9 shows that the half of the weight is only due to the battery and that the structure constitutes also an important part that increases with wingspan as said before. This knowledge allows putting efforts on the critical instead of working on elements that play a minor role in overall mass. André Noth and Roland Siegwart 13
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