Variable Pitch Propeller

Some innovative aspects of aircraft were first proposed long before airplanes were actually flying. One of these is the variable-pitch propeller, which, as its name suggests, changes the pitch of the propeller blades (the angle at which they cut through the air) in order to produce more thrust.

The biggest problem with all of the early designs was wear and tear. Although they could work in flight, they did not work for long, and the bigger and more powerful the engine, the faster they wore out. Designers thus had to limit these to relatively small engines.

W.R. Turnbull, born in St. John New Brunswick,  first proposed using an electric motor to vary the pitch of the propeller. The advantage to this design was that it did not require any modifications to the engine itself to provide the oil to power a hydraulic mechanism. He designed his first system in 1925 and tested it in 1927. The tests were successful and the American company Curtiss-Wright licensed the design and began to modify it, but it took several years before the company began to incorporate the new propeller into its Navy and Army Air Force aircraft. The Curtiss-Wright propeller soon became a rival for the Hamilton-Standard propellers.

information gathered from http://www.centennialofflight.gov/essay/Evolution_of_Technology/props/Tech14.htm