Re: gurney flaps

Date:         17 Dec 96 03:09:15 
From:         David Lednicer <dave@amiwest.com>
Organization: Analytical Methods, Inc.
References:   1
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nicole wrote:
>
> hi, i'm trying to find more about gurney flaps and don't know where to
> get started - they don't seem to be in any of my aero textbooks.  anyone
> have any suggestions? could you please email me with them?
> thanks, nicole

	Bob Liebeck of Douglas is credited with first bringing them to
the attention of the aerodynamics community, but they are named after Dan
Gurney, the famous race car driver.  Several years ago, sitting in the
bar avoiding attending paper sessions at an AIAA meeting, I asked Bob for
the full story.  He told me that Dan Gurney suggested to him the idea,
based upon the old "spoilers" added to the aft end of race cars in the
late 1960s.  These "spoilers" were simply sheet metal tabs, added to the
end of the rear deck, projecting upwards.  Gurney reasoned that if, they
worked there, why wouldn't they work on the trailing edges of wings?
They tried the idea and it worked!  For a flap that was 1-2% of airfoil
chord, projecting perpendicular to the airfoil trailing edge, they got a
useful increase in lift (downforce for a car), without much drag
increase.  Bob first published the concept in a 1976 AIAA paper (76-406).
This was later reprinted in the September 1978 AIAA Journal of Aircraft.

	When the flaps first showed up at the Indy 500 on Gurney's cars,
competitors asked him what they were for, so Gurney had an explanation
ready.  "When we push the car out, with our hands on the trailing edge of
the aft wing, we tend to get cut up, so we added this tab to blunt the
trailing edge."  Competitors thought that this was a good idea, but they
put their tabs on projecting downwards, rather than upwards, as needed to
improve downforce!  It was several years before they caught on.

	Actually, designers have used strips on the trailing edge of
control surfaces before, which look much like Gurney flaps.  However,
they were intended to reduce control surface oscillation caused by
wandering separation patterns.

-------------------------------------------------------------------
David Lednicer             | "Applied Computational Fluid Dynamics"
Analytical Methods, Inc.   |   email:   dave@amiwest.com
2133 152nd Ave NE          |   tel:     (206) 643-9090
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