What is the feathering capability in controllable pitch propellers?

The feathering capability in controllable pitch propellers refers to the ability to adjust the pitch of the propeller blades so that they align edge-on with the airstream. This position minimizes drag significantly, especially in the event of an engine failure, allowing the aircraft to maintain control while reducing the aerodynamic drag imposed by a windmilling propeller. By pointing the blades into the wind, the propeller essentially "feathers," which helps in improving aircraft performance and safety during critical phases of flight, such as descent or glide.

Feathering is particularly useful in multi-engine aircraft, where one engine might fail, allowing the operative engine to be more efficient while reducing the drag created by the inoperative engine's propeller. This capability is an important feature of controllable pitch propellers, as it enhances performance and can prevent further loss of altitude and control after an engine failure.