In this paper, the author has first shown the increasing need, amounting in many instances to a necessity, for the adoption of the controllable pitch propeller on modern airplanes. Improvements in airplane design which bring about increased speed range have brought about a decrease in other performance items which can only be rectified by the use of the controllable pitch propeller. The improvement has been shown to be so great as to well pay for the added complication and expense involved.
The several types of controllable pitch propeller developed in this country are described, the author going into considerable detail on the electric-driven type.
The numerous test requirements are gone into in detail. In conclusion, the author notes greater progress in the development of the controllable pitch propeller in this country than elsewhere, perhaps necessitated by the accompanying advance in aerodynamic refinements here developed.
