Transport: Full Feathering

By changing the design of its propellers (deepening the pitch and adding a fourth blade), the S. S. Normandie last month recaptured the Atlantic speed record (TIME, Aug. 16). Even more striking are the results that have been attained in the last four years by changing the design of airplane propellers. Until 1933 there had been only two major improvements in the paper airscrew invented by Leonardo da Vinci some 450 years before to pull toy helicopters to the ceiling of his study. One was the Wright Brothers’ development of a two-bladed ‘”prop” of laminated wood, the other the shift in the 19205 to aluminum alloy blades whose pitch could be adjusted on the ground to suit various operating conditions. In 1933 the Hamilton Standard Propellers division of United Aircraft Corp. won the Collier Trophy by producing the first controllable pitch propeller, ”the gearshift of the air.” This allowed a pilot to change propeller pitch during flight and achieve maximum propeller efficiency both at take-off and at high speed. A further refinement was the constant speed propeller, which changes pitch automatically as the plane climbs, dives or cruises so that the engine’s r.p.m. remain constant.

Until recently Hamilton has had a virtual monopoly of the propeller business. Lately, however, it and its most formidable rival, famed old Curtiss-Wright Corp., have been seeking another propellerimprovement—full feathering of the blades. Curtiss-Wright devised an electric motor which nestles in the hub of the propeller and changes the pitch to any angle from o° to 90° whenever the pilot wishes. If an engine fails, the pilot merely adjusts the propeller pitch to 90°, which means that the blades feather (present a streamlined knife-edge to the wind), do not revolve. This is important because when a motor fails the airflow makes the dead propeller “windmill,” which usually damages the disabled motor just as pushing an automobile forward with gears meshed but engine dead may strip the gears. Tried out on several military types by both army and navy, the new propeller last week won a fat contract from the Army—240 for an average price of $2,134.42 apiece.

Spurred by Curtiss-Wright’s success, Hamilton Standard last week revealed that it too has a full-feathering prop. Worked by hydraulic pressure, the Hamilton blade has been ordered in small quantities by United and American Airlines for twin-motored use, by Pan American for its vast four-motored Boeing Clippers now abuilding in Seattle.