An ornithopter from the ancient Greek language is an aircraft that flies by flapping its wings. Designers try to make the flapping-wing flight of birds, bats, and insects seem real. Though machines may differ in form, they are usually built on the same scale as these flying creatures. Manned ornithopters have also been built, and some have worked. The machines are of two general types: those with engines, and those powered by the muscles of the pilot.