One of Leonardo da Vinci's many sketches in his notebooks was a flying machine. The design of this ornithopter, an aircraft powered by flapping wings, was inspired by the flight of bats and birds. It was designed that the pilot would lay down on their stomach and power the machine using levers, pedals and pulleys with their hands and feet to make the large wings flap. Scientists today know that the design would never have enough power to make it off the ground. The materials would be too heavy and the pilot would not be able to generate enough energy for a successful flight. Image source: Wikimedia Commons, Design for a flying machine, image labeled as public domain in the United States because it is a photographic reproduction of a public domain work of art.