University of Virginia Library

Why Blades Are Curved.

It has been pointed out by experiment that certain forms of curved surfaces as applied to aeroplanes will lift more per horse power, per unit of square foot, while on the other hand it has been shown that a flat surface will lift more per horse power, but requires more area of surface to do it.

As a true pitch screw propeller is virtually a rotating aeroplane, a curved surface may be advantageously employed when the limit of size prevents using large plane surfaces for the blades.

Care should be exercised in keeping the chord of any

curve to be used for the blades at the proper pitch angle, and in all cases propeller blades should be made rigid so as to preserve the true angle and not be distorted by centrifugal force or from any other cause, as flexibility will seriously affect their pitch speed and otherwise affect their efficiency.