<div class="htmlview paragraph"><b>THE feathering propeller meets two fundamental needs in airline operation which the constant-speed propeller cannot meet, the authors explain. First, by stopping the rotation of an engine and propeller in flight, it protects the airplane from catastrophic vibrations occasionally set up by mechanical failures of engine and propeller. And the second fundamental need, they state, is that the feathering propeller decreases the drag of an inoperative propeller, thereby increasing the performance of a multiengined airplane with one or more engines inoperative. For these reasons, they point out, the feathering propeller has been accepted by leading airlines as the answer to their immediate propeller needs.</b></div> <div class="htmlview paragraph"><b>In this paper the full-feathering principle is explained as applied in two distinct propeller designs.</b></div> <div class="htmlview paragraph"><b>Performance figures are given for twin-engined air-transport planes with and without feathering propellers, and the importance of the feathering propeller in the operation of four-engined airplanes and its beneficial effect upon their twin and triple-engine performance are pointed out. Propeller icing, pertinent flight test data, the value of the feathering propeller in studying propeller ice in flight, and future propeller design trends, also are discussed by the authors.</b></div>