The evolution of camera drones
Drones, a class of flying machines, evolved from remote-control aircraft. They first (1) ________ as commercial camera devices around twenty-five years ago, and became widespread only twenty years later, around the same time as smartphones. In a new study, scientists have shown how they steadily developed and became twice as efficient at flying over the (2) ________ of their existence. Product records, combined with a new (3) ________ of flight based on modern helicopters, were used to measure the machines' flight efficiency and to (4) ________ how they developed over time. The findings showed their development was caused by consistent small improvements over a long period rather than the sudden technological (5) ________ which had previously been suggested. Over their short commercial history, drones' body shape and size (6) ________ to use 50% less energy during flight. They increased in range by ten times, with some (7) ________ carrying more than thirty kilograms. However, according to the study, there is one group of drones - quadcopters - whose recording ability is (8) ________ to have remained rudimentary in comparison with professional drones.