Airscrew development has proceeded along four main lines :–
(1) Aerodynamic design.
(2) Materials.
(3) Adaptation to engine and aircraft.
(4) Fans for cooling and ventilating purposes.
Section (4) I have omitted. It may form the subject of a paper elsewhere. Section (1) I have barely outlined. It is of great interest, but I have concentrated on Sections (2) and (3) as being of immediate practical concern.
Note on page 492 * For a qualification of this statement, see Appendix.