Current flying objects face a trade-off: Drones with propellers, for instance, are very agile and able to hover; however, they use up a lot of energy. Airplanes, on the other hand, feature fixed wings that allow them to fly very efficiently. The downside: They can’t remain suspended in the air like a kestrel on the lookout for prey.Current flying objects face a trade-off: Drones with propellers, for instance, are very agile and able to hover; however, they use up a lot of energy. Airplanes, on the other hand, feature fixed wings that allow them to fly very efficiently. The downside: They can’t remain suspended in the air like a kestrel on the lookout for prey.[#item_full_content]