Newsgroups: sci.aeronautics.airliners
From: David Lednicer <dave@amiwest.com>
Subject: Re: unpowered glide ratios
Date: 25 Oct 94 10:24:06

	As to why a windmilling jet engine produces less drag than a
stopped jet engine vs. a stopped prop produces less drag than a
windmilling prop:

	Not much air gets through a stopped jet engine, resulting in very
high spillage drag (kinda like holding a coffee mug open end first into
the wind).  A windmilling jet engine passes more air, reducing the
spillage and hence the drag.  On the other hand, a stopped prop is
usually feathered, which is very low drag.  A windmilling prop has more
blade surface area exposed and has higher drag.  The difference boils
down to the fact that the jet engine is contained within a nacelle, while
the prop is completely out in the freestream and that the prop has
variable pitch, while the jet engine blades are not variable pitch
(ignoring variable pitch stators).


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David Lednicer             | "Applied Computational Fluid Dynamics"
Analytical Methods, Inc.   |   email:   dave@amiwest.com
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