Originally Posted by Scott Skylane

Flanagan wrote:
/snip/
Can anyone clarify this? Does one feather an engine simply to reduce
the drag generated by the angle of the propeller, or it is also to stop
the engine from turning? If the latter is correct, why?

Thanks to everyone.




Flanagan,

To clarify, the term "feathering an engine" actually means "feathering
the propeller". The blades of the prop are twisted in the hub such that
they are parallel with the airflow, and thus present minimal drag, to
assist the aircraft in continuing flight with one less powerplant in
operation. As a result of this, no lift is generated by the blades, and
thus the prop, and the engine it's attached to, stops rotating. As an
aside, the drag created by a windmilling propeller, i.e. one not
feathered and attached to a dead engine, creates as much drag as a flat
plate the same size as the area of the prop arc.

To answer your question, yes, stopping engine rotation is desireable for
several reasons. If the engine was experiencing some sort of internal
failure, stopping rotation will contain damage to whatever component was
affected, and hopefully preserve the rest for future use. If the engine
was on fire, and the aircraft is equipped with fire fighting agent, you
want to stop the airflow from the prop, as it tends to dissipate the
agent, instead of letting it do it's work. And obviously in the case of
fire, a turning engine may well pump more fuel in to the conflagration
to begin with.

Hope this helps.

Happy Flying!
Scott Skylane