The high engine output necessary in order to effect further increases in flight speed must be transformed in the fullest possible measure by the airscrew into propulsive power. Three possibilities are open whereby the capacity of the airscrew for absorbing the engine power may be increased, namely, (1) by increasing the diameter, (2) by increasing the number and width of the blades, and (3) by increasing the peripheral speed. The increase in the diameter is limited by the effects of weight, the increase in the number and width of the blades by considerations of structure and design and the increase in the peripheral speed by the speed of sound. Of these limitations the last is of particular importance.