"Morgans" wrote in message
...

"Flanagan" wrote

It is so kind of you to reply, and your explanation is so interesting.
Thank you!

In addition, I would add that though it seems counter intuitive, a
rotating unfeathered prop has more drag (much more) than a unfeathered
prop that is not rotating. The feathering has two bonuses, in sorts then.

An unfeathered prop has lower drag stopped, so feathering the prop stops
the prop for the first reduction in drag, and feathering it after it is
(or during stopping it) reduces drag even again.

The reasons given about lessening damage, although true, are a very very
distant reason on why to feather. The MOST important reason is to reduce
drag, increase time in the air and gliding distance, because both of those
reasons mean LIFE. Never seen a better reason than that one, yet. g
--
Jim in NC

Very well said.

I am sorry that I cannot currently recall a source to document the
information. But considerable work has been done to document the rate and
angle of descent of light aircraft with a fixed pitch propeller idling,
windmilling, and stopped.

To the best of my recollection, the descent with the propeller stopped was
very similar to the descent with the engine idling; but the descent with the
propeller windmilling was considerably steeper.

In addition, some testing was docummented in one of the aviation magazines,
possibly Flying, in which a Cessna 172 or 152 (I have forgotten which) was
equipped with a steamlined fairing in place of the propeller and spinner.
The aircraft was towed then towed aloft and released so that the gilde
performance of the aircraft could be separated from the effects of the
engine and propeller.

However, in the particular case of the radial engines on the B17 and B24,
windmilling engines normally occurred in cruising flight as the result of a
loss of oil and consequently of oil pressure. In such cases, the engines
would overspeed until they seized and the propeller assembly would then
shear off of the affected engine. If you were lucky, it would then drop
straight down; but if you were not lucky considerable damage would
result--including serious injuries or deaths of crew members and
occasionally the loss of the aircraft. Bcak in the day--during the war--the
aircraft were in typically cruising in formation when that occurred, so
there was little opportunity to attempt anything other than to evacuate the
crew positions alligned with the propeller arc. Occassionally, in the
present time, something similar still happens involving the few remaining
DC3 and similar aircraft still in service; and the aircraft are frequently
lost by pilots attempting to avoid overspeeding the (failed) engine.

Peter