Propeller Feathering and Reverse Systems

Propeller Feathering Explained

Feathering a propeller means rotating the blades so they are nearly parallel to the airflow. This greatly reduces drag if an engine fails, preventing the windmilling effect that can compromise control and increase descent rate. Feathering is usually achieved by pulling the propeller or condition lever fully rearward into a gated feather position. In single-acting systems, feathering relies on springs and counterweights, while double-acting systems use oil pressure for positive blade movement. Some aircraft feature auto-feather systems, automatically feathering a propeller when engine torque drops below a set threshold during critical phases like takeoff.

Unfeathering is the process of returning the blades to a normal operating angle, typically using stored oil pressure or an electric pump to drive the blades out of feather, allowing the engine to be restarted in flight.

Propeller Reverse Systems

Reverse thrust is used primarily after landing to shorten stopping distance. By selecting reverse on the power lever, the propeller blades are moved to a negative pitch, redirecting airflow forward and generating braking force. The direction of propeller torque remains unchanged, but the thrust vector is reversed. Reverse selection is only possible on the ground due to safety interlocks.

There are different types of thrust-reverser systems, including:

• Hot-stream reversers (redirecting exhaust gases)
• Clamshell or bucket-door systems
• Cold-stream reversers (for high bypass turbofans, only reversing the fan airflow)
• Blocker doors and cascade vanes (redirecting bypass air forward)

Controls for reverse thrust are typically integrated into the power lever, with clear cockpit indications showing when reverse is selected and active.

Feathering vs Reversing

Feathering is a safety measure for engine failure, while reversing is an operational tool for ground deceleration. Both require precise control and understanding of the propeller system architecture.