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From: David Lednicer <>
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).

David Lednicer             | "Applied Computational Fluid Dynamics"
Analytical Methods, Inc.   |   email:
2133 152nd Ave NE          |   tel:     (206) 643-9090
Redmond, WA  98052  USA    |   fax:     (206) 746-1299

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