Jim Logajan wrote:
Orval Fairbairn wrote:
wrote:
Scott Skylane wrote:
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.

Nope. The blades cannot be everywhere at once, and so the area
affected is no larger than the blade area.

YES! In aeronautical engineering analysis, a windmilling prop is
considered to be a flat disk, with drag numbers to match. Feathering
the prop greatly reduces drag.

Three answers not entirely correct, none entirely wrong - how can this be?
Because as shown by simple empirical measurements, "it depends" as
indicated in this thesis:

http://www.goshen.edu/physics/PropellerDrag/thesis.htm

(Scroll down to review figures 11 through 14 if you are in a hurry. Figure
13 label provides a summary relevant to this thread.)

As the author of that thesis noted:
"The available publications and information in the area of propeller drag
are almost non-existent, not because of any difficulties of the research
sophistication, but because of the simplicity of it. To investigate
propeller drag one does not need electronics and a large grant, one only
needs a wind tunnel and a spring for a quick measurement. Therefore, most
of the research in this field was done before articles were indexed as they
are now. It was not until I found some journals from the 1930's that I
could actually piece together trails of research."

True that propeller research went away around WWII, but wind turbine
research is currently a hot topic and that's what the propeller becomes
when the engine stops.


--
Jim Pennino

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