In article ,
"R.W. Behan" wrote:

No. First: your example in the DC-3 included *feathering*; changing the
AOA to zero.

Ask yourself: how could it make a difference to drag to have such a prop
locked or free to spin?


Alan, look. Feathering an airplane propeller does indeed change the angle
of attack to zero, but that is how you STOP the autorotation. In a boat,
you stop the autorotation by shifting to reverse. The purpose in either case
is the same: to reduce drag.

Your second statement is a non-sequitur. There's no way in the world a
feathered prop CAN spin, right?

Good. You're starting to see.

Now. Change the angle of attack minutely. The propellor now
"auto-rotates", right?

Now. Is the amount of drag it is going to generate the same as the
amount of drag it would generate at a much larger AOA?

Answer that question correctly and then perhaps you'll see that you
can't simply equate the drag of a free-spinning propellor to a solid
disc of the same size as the props diameter...


Cheers. It's a lively discussion.

Dick



--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."