Re: unpowered glide ratios

From:         David Lednicer <>
Date:         25 Oct 94 10:24:06 
References:   1 2 3
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	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