What is a Fixed Pitch Propeller?
A one-piece propeller with a single fixed blade angle. The pitch (blade angle) must be high enough to offer good cruising performance yet low enough to achieve acceptable takeoff and climb characteristics.
What is a Constant Speed Blade?
A propeller used with a governor, that automatically provides constant RPM by controlling the forces acting on the propeller to change the blade angle within a preset range.
What is a Full-Feathering Blade?
A propeller which allows blades to be rotated to a high positive angle to stop rotation (wind milling) after an engine is shut down, thereby reducing drag and asymmetric control forces on twin-engine applications.
What is Blade Pitch?
Pitch is changed hydraulically in a single-acting system, using engine oil controlled by the propeller governor to change the pitch of the propeller blades. In constant-speed systems, the pitch is increased with oil pressure. In full-feathering systems, the pitch is decreased with oil pressure. To prevent accidentally moving the propellers to the feathered position during powered flight, which would overload and damage an engine that is still running, the controls have detents at the low RPM (high pitch) end.
In a single-acting propeller system, oil pressure supplied by the governor, acting on the piston produces a force that is opposed by the natural centrifugal twisting moment of the blades in constant speed models or counterweights and large springs in full-feathering systems. To increase or decrease the pitch, high pressure oil is directed to the propeller, which moves the piston back. The motion of the piston is transmitted to the blades through actuating pins and links, moving the blades toward either high pitch for constant-speed systems or low pitch for full-feathering systems.
When the opposing forces are equal, oil flow to the propeller stops and the piston also stops. The piston will remain in this position, maintaining the pitch of the blades until oil flow to or from the propeller is again established by the governor.
From this position, pitch is decreased for constant-speed systems or increased for full- feathering systems by allowing oil to flow out of the propeller and return to the engine sump. When the governor initiates this procedure, hydraulic pressure is decreased and the piston moves forward, changing the pitch of the blades. The piston will continue to move forward until the opposing forces are once again equal. Mechanical stops are installed in the propeller to limit travel in both the high and low pitch directions.