On 2007-02-07, Mxsmanic wrote:
If a prop is feathered and an engine is shut down, will the engine
windmill at all?

I assume that a windmilling prop still turns the engine (i.e., no
clutch disconnects it from the engine, at least on a piston
powerplant). If so, can windmilling drive an alternator enough to
provide useful electrical power?

With piston engines, when the prop is feathered (hence blades are more
nearly parallel with the wind) there is usually enough compression in the
engine to prevent the blades from turning. This might also depend upon how
completely the blades feathered.

So even if the prop turned at all there would not be enough rotation for the
alternator to be of any use. Also, in an emergency all electrics may be
turned off anyway to prevent fire hazards.

With turboprop engines there are two types. Engines like Garretts have the
props connected by planetary gears to a shaft and both the compressor and
exhaust turbine blades are connected to the same shaft with no breaks in the
shaft. Accessories, such as starter/generators and other pumps are connected
to this via gears. This is called a fixed shaft turbine.

My experience is with a Commander 840 with -10 Garretts and when the props
are feathered there is a very slow turning of the props, but not enough to
effect any generation of current.

The second type of turboprop would be like the Pratts where the prop is
free-wheeling (free turbine) and the connection to the actual engine is via
two sets of blades positioned in front of each other, one set on the shaft
to the engine and the other set to the prop. I'm not as familiar with this
engine, but whether or not the prop rotated, it isn't connected to
accessories anyway so of no use.

Remember than when an engine is shut down in flight, whether intentional or
not, all electrical to the engine might be shut down, including any fuel
pumps, generators, etc., (and usually is) in handling the emergency to
prevent other problems, such as fire.

....Edwin
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"Once you have flown, you will walk the earth with your eyes
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