Engineers from the Australian Centre for Field Robotics in Sydney are working on an autopilot system for gliders that senses thermals and adjusts its course, utilizing the thermal currents to stay aloft. Couple that ability with the technique of dynamic soaring, where the glider flies between high and lower speed air currents to keep it aloft when thermals aren't readily available, and perpetual flight might become a reality sooner than we ever could have imagined.
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That will pair up nice with the current perpetual waiting that the airlines have already perfected.