This was exactly my research in gradschool. Sorry to self promote, but it's not often I get a chance to discuss my incredibly esoteric dissertation topic. I was part of a team working to get a UAV to perform a dynamic soaring maneuver, which allows an aircraft (or bird) to extract energy from wind gradients to support flight [1].
DS was first recognized in the albatross by Lord Rayleigh. Like the frigate bird in this artcle, the albatross is able to expend very little enegery while traveling great distances, thanks to its oceanic environment. Close to the ocean surface, friction between the wind and the water causes windspeed to slow. As you move up in altitude, windspeed increases. So you have this nice gradient that is always there for the albatross to take advantage of. The albatross locks its wings into place (using a big tendon sheath), and it performs successive climbing/diving maneuvers through this gradient, netting it kinetic energy at the end of each cycle.
So my role in the project was the brains behind a soaring aircraft, which was being developed in tandem. I'm a little fuzzier on the specifics of how the aicraft was made, but it was a novel manufacturing process that allowed us to build very large, seamless carbon fiber wings [2].
As part of my work, I had to figure out how to find trajectories that would support flight, given an aircraft. I also had a formulation that would find an optimal aircraft as part of the solution. The key takeaways for the aircraft are very large wingspan, and also some heft to the airframe; you don't want the aircraft being too light, because most of the energy gain comes during the transfer between potential -> kinetic energy during the dive phase of the maneuver.
Anyway, anyone really interested in the topic can take a look at our publications [3]. We looked at soaring in the jetstream, soaring in hurricanes, even reinforcement learning for a UAV to figure out how to soar better.
[1] http://www.popsci.com/technology/article/2013-06/future-flig... [2] http://vader.cse.lehigh.edu/dynamicsoaring/wp-content/upload... [3] http://www.dynamicsoaring.lehigh.edu/