Re: Leading Edge fences

Date:         10 Sep 97 19:38:43 
From:         David Lednicer <dave@amiwest.com>
Organization: Analytical Methods, Inc.
References:   1
Followups:    1
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BAEJS3201 wrote:
>
> Hey out there can anyone answer a question for me??? I've noticed that
> aircraft with aft mounted engines(727,DC9/MD80 and maybe Fokkers)have what
> looks like a fence on the leading edges of the wings. Is this to straighten
> the airflow for the engines????

	Usually, wing fences are to control the spanwise flow on the
wing at stall.  Those on the F28, 727, Gulfsteam II, etc. are for
exactly this purpose.  The DC-9 has something called a Vortilon.  This
is a fence-like object on the lower surface of the wing, slightly aft of
the leading edge.  At low angles of attack, it does little, but near
stall, it sheds a vortex that helps increase the effectiveness of the
horizontal tail.  This helps enable the aircraft to be recoverable from
what would otherwise be a locked-in deep stall.

	The Douglas engineers developed the Vortilon by noticing how the DC-8
wing stalled differently in the tunnel with and without engine pylons.
The Vortilon started out as just a stub pylon.

	A side note: retroactive renaming is happening!  I was on an Alaska
Airlines flight Monday where the pilot identified the aircraft, over the
PA, as a "Boeing MD-80".

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