Re: 727 inboard leading edge devices

Date:         01 Dec 97 02:33:50 
From:         Simon Ellwood <>
Organization: Bodge It & Co. Ltd.
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In article <airliners.1997.2831@ohare.Chicago.COM>, Andrew Goldfinger
<> writes
>     The inboard leading edge devices on the 727 do not deploy by sliding
>forward as do the devices on most other aircraft.  Instead, they rotate
>downward and outward pivoting near the leading edge.  Intuitively, this
>bothers me.  With a "sliding" device, the change in wing shape during
>deployment seems more continuous to me.  Do the 727 devices do strange
>things to the aerodynamics when partially deployed?  Why were the devices
>made in this way?  Is there a name for this type of device?

The inboard devices are known as Kruger flaps, whilst the outer devices
are standard slats. The Krugers are normally flexible and form a LE
shape during deployment. Aircraft such as the 707 & 747 have only these
Krugers - no slats.

Both devices increase lift by increasing the curvature and camber of the
wing at the LE. However, when the slat is fully deployed, it leaves a
slot between itself and the LE of the wing. This slot effectively
accelerates flow over the wing LE, increasing the energy in the boundary
layer flow.

The upshot of all this is that the stall angle of the slatted part of
the wing is increased, and thus on an aircraft like the 727, the wing
roots stall before the tips. This has the advantages of :-

1) Preventing tip stall and roll when the aircraft stalls.

2) As the root stalls before the tips, and the 727 has a sharply swept
wing, a strong pitch down is induced from the "still flying" tips which
are a fair way behind the CG.

Has anyone noticed that on the 727 the no.s 2,3 and 6,7 slats deploy
first at a lower flap setting than the rest of the slats and Kruger's ??
Can any of you Boeing engineers tell us why ??

Simon Ellwood