The Fundamental Technical Problems in Early Attempts at Vertical Flight

Six fundamental technical problems can be identified that limited early experiments with helicopters. These problems are expounded by Sikorsky (1938, and various editions) these problems were:

1.Understanding the aerodynamics of vertical flight. The theoretical power required to produce a fixed amount of lift was an unknown quantity to the earliest experi­menters, who were guided more by intuition than by science.'

2.The lack of a suitable engine. This was a problem that was not to be overcome until the beginning of the twentieth century, through the development of internal combustion engines.

3.Keeping structural weight and engine weight down so the machine could lift a pilot and a payload. Early power plants were made of cast iron and were heavy.

4.Counteracting rotor torque reaction. A tail rotor was not used on most early designs: these machines were either coaxial or laterally side-by-side rotor configurations. Yet, building and controlling two rotors was even more difficult than for one rotor.

5.Providing stability and properly controlling the machine, including a means of defeating the unequal lift produced on the advancing and retreating blades in forward flight. These were problems that were only to be fully overcome with the use of blade articulation, ideas that were pioneered by Cierva, Breguet, and others, and with the development of blade cyclic pitch control.

6.Conquering the problem of vibrations. This was a source of many mechanical failures of the rotor and airframe, because of an insufficient understanding of the dynamic and aerodynamic behavior of rotating wings.