Re: Trailing edge wedge?

Date:         19 Apr 99 02:22:38 
From: (Neil Wagner)
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On 30 Mar 99 01:54:01 , wrote:
>It seems surprising there are still relatively easy 7% improvements laying
>around.  Does anyone know what this wedge is, and the basic idea behind
>it?  Why is it only being introduced now?

I too was surprised to see such a large percentage improvement quoted.
The wedge was used on the MD-11 from nearly the first ship delivered.
Boeing apparently didn't learn of the great benefit until they
"borrowed" some of Douglas' engineers from Long Beach just prior
to the Boeing-McDonnell Douglas merger.

On the MD-11 the wedge is exactly that.  Instead of the trailing
edge of the wing control surfaces ending in a triangular "point,"
the trailing edge was designed to be a constant thickness of about
an inch over the aft-most 6 inches or so of the chord.  The extra
thickness is below the natural chord line.  I don't remember
the specific details of the concept, but I think the idea is
to direct the airflow downward locally, rather than straight
back.  In essence the camber of the wing is increased right at
the trailing edge for an overall increase in total lift produced
by the wing.  I'm told of a side benefit of the swirling air
coming off the upper and lower surfaces of the wedge actually
imparting forces in a forward direction on the aft surface of the
wedge, resulting in less fuel being used to push the plane through
the air.  A similar idea is used in the outflow valve, wherein the
expelled air is directed in an aft direction, resulting
in "recovered thrust."

Neil -