The possibility of sustained flight by heavier-than-air-machiaes was fully recognised during the last century by those who had studied the aerodynamic problems involved and it was realised that its accomplishment awaited only the development of a prime mover of sufficiently light weight.

Of all the known forms of prime mover, the internal combustion engine alone held out any promise of fulfilling the conditions necessary .for sustained flight, namely, light weight not only of the engine itself but also of the fuel it consumes. Early attempts had, however, been made to fly with steam, propulsion and it is of interest to note that the very remarkable and cleverly-designed steam plant employed by Sir Hiram Maxim in 1894 was actually very considerably lighter per h.p., even including the boiler and condenser, than the petrol engine used successfully some nine years later by the Wright Brothers.

Many books on aerodynamics are prefaced by a short historical introduction, in which, after having quoted Aristotle for his ideas on the motion of bodies through the air, and Newton, from whom aerodynamics is admitted to start, the name of Leonardo da Vinci is recorded, pointing out that he was the first to attribute to the resistance of the air the cause of the lift and flight of birds, recognising in the same resistance the possibility of solving the problem of flight.