EVOLUTION OF PROPELLER PITCH-CHANGE MECHANISMS

Evolution of Propeller Pitch-Change Mechanisms



Evolution of Propeller Pitch-Change Mechanisms

Introduction/Scenario

Turbo-prop aircraft have seen a recent increase in popularity with operators, due mainly to their exceptional fuel economy. The technological advances of the propeller since their first successful use have been remarkable, and include the areas of pitch control and blade design. Modern pitch control mechanisms give greater control and thus efficiency, whilst design has changed dramatically since the first paddle-shaped blade. However, designers still strive to produce unit capable of absorbing the power of modern engine whilst keeping noise levels as low as possible. This paper discusses the following two points in a concise and comprehensive way.

I-The Evolution of Propeller Pitch-Change Mechanisms from the First Record Flight to Modern-Day Systems

Ya-Jung and Ching (2004) mention that 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 first proposal for a variable-pitch propeller was made in 1871 by a Frenchman named J. Croce-Spinelli. Croce-Spinelli proposed a design for a propeller whose pitch was changed by hydraulic pressure (forcing oil through a tube). Croce-Spinelli claimed that this would be most useful during takeoff, when an airplane needed the most power (Croce-Spinelli was one of two men who died in 1875 when they went too high in a balloon). Another Frenchman, Alphonse Pénaud, also proposed using a variable-pitch propeller in his patent on airplane design in 1876 (Ya-Jung and Ching, 2004).

Many of the people who worked on airplane design for the next several decades, both before and after the Wright brothers took flight in 1903, recognized the obvious advantages of the variable-pitch propeller, which could change the engine thrust without having to change the engine power and the speed of the propeller. But nobody could make it work until 1910, when the first variable-pitch propellers were used on some airships. Airships used the propellers to reverse thrust, so that they could slow down rapidly and even back up. But these early designs were not safe enough to use on airplanes.

As engine horsepower increased post World War I, the wooden fixed-pitch propeller that operated efficiently only at its design speed was no longer enough.

Around 1917, mechanically controlled variable pitch propellers were under development in Great Britain and Germany. These propellers solved the problem of changing the engine thrust without having to change the engine power and speed of the propeller. However, the bigger and more powerful the engine, the faster the variable pitch propeller wore out. By the 1920s, designers had abandoned the mechanically controlled variable-pitch propeller (Ya-Jung and Ching, 2004).

An American engineer, Frank W. Caldwell, developed a propeller that had detachable blades joined to a central hub. This allowed pitch adjustments to be made while the plane was on the ground. This ground-adjustable propeller proved to be crucial to the success of Charles ...