The flying-machine sketch shown in Figure 2.1 is one of more than 500 sketches concerning flight that survivefrom the notebooks of Leonardo da Vinci (1452-1519). Dating from the period 1486-90, it shows a device designed to be powered by a man, with the wings being flapped up and down and back and forth to provide lift and thrust simultaneously. Such machines are called omithopters.

Da Vinci had a variety of such designs, with the pilot either lying prone (as in Figure 2.1) or dangling vertically under the machine as in a modern-day hang glider. In all cases the pilot would supply the motive power with arm, leg, or torso movements that would be mechanically translated into flapping of the wings. At first glance, the ornithopter in Figure 2.1 would appear to have no redeeming aerodynamic value – it is so contrary to our modern ideas about airplanes. On the other hand, it was the first serious design for a flying machine, and it is chosen as the seminal development from which to focus the historical discussion in this chapter.

Looking more closely at da Vinci's flying machine (Figure 2.1), we see an ornithopter in which the pilot lies prone and operates the wings by pushing and pulling a variety of levers. The wings themselves are essentially wooden spars; we can surmise that he intended some fabric covering for the wings in order to increase the area of the lifting surface. We know that he drew pictures of wings covered with net-like fabric. Figure 2.2 shows an ingenious da Vinci idea for independently testing an ornithopter wing: On one pan of a balance there would be a man and a wing, and weights would be placed on the other pan until the two were in balance.