What does it mean when an aircraft feathers?

[Dragonmount 5]

I have two aircraft where "auto feather" is a feature in FSX, and I was curious what is it?  (the majestic q400, and the PMDG js41)

[JNS 106]

Autofeather is a feature of the engines on some turboprop or piston engine aircraft. When the power being produced by the engine drops to the point where it is not contributing to thrust, the propeller will go into a feathered mode to reduce drag.

The auto feather system also allows pilots to reduce the drag (changing pitch of blade so that it is parallel to airflow) of the propellers during an engine failure, therefore, allowing the plane to glide for a longer period of time.

An automatic feathering system was first introduced on the Martin 4-0-4 aircraft, a piston engine airplane. The system was designed to automatically feather an engine that failed during takeoff or initial climb.

[FormerSF3 15]

JNS has and excellent description. 

 

I will add that some of these features have been added to certain aircraft so they can make the climb gradient if the engine fails just after liftoff.  Its also a safety feature so you don't have pilots throwing levers close to the ground.  See the accident info on TransAsia.

[fs4fun 366]

I think auto feather is why you need to get the props on to the start locks with the J41. The feathered position causes excess drag during engine start and as a result the engines can overheat and catch fire. The start locks keep the prop from feathering even when the engines are shut down.

[HighBypass 2,339]

I have another aircraft which has autofeather working in FSX - the beautiful Piaggio P180 Avanti by Mario Noriega (freeware).

 

Here's a typical photo of a real one - one engine running the other not yet so the prop is feathered:-