A major challenge is the design and construction of a structure that can embed the 0.5 [kg] payload and at the same time can be folded in a &empty 1 x 0.4 [m] cylinder. It must therefore combine lightweight and robustness. The original approach we chose to reach this goal is to team up with experts from various fields, from aerodynamic modeling up to lightweight model airplanes design. This allowed us to push the limits of the overall systems design, using latest findings in all key technologies. The starting point for the demonstrator design was the model airplane of Walter Engel that holds the world record for flight duration of over 15 hours with 1 kg of battery.

The resulting Sky-Sailor version 1 has a structural weigh of only around 0.6 [kg] for a wingspan of 3.2 [m] and a wing surface of 0.776 [m²] (see Fig. 5). The resulting total weight including motors, solar cells, batteries, controller and payload is around 2.5 [kg].