Re: 727 inboard leading edge devices

Date:         01 Dec 97 02:33:51 
From:         darren@daz-technology.demon.co.uk (Darren Rhodes)
Organization: Daz Technology
References:   1
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On 29 Nov 97 15:40:04 , Andrew Goldfinger <Andy.Goldfinger@jhuapl.edu>
wrote:

>     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 device you refer on the inboard wing section is of the Boeing 727
is a Krueger flap (named I believer after a German (?) aerodynamicist.

The Boeing 747 also has them on the inboard section of the leading
edge too. They are less efficient at delaying stall than leading edge
slats (the ones you refer to as sliding forward) but are mechanically
simpler and lighter. However, that is not the over-riding reason they
are used since all Airbus and all new Boeing aircraft now use full
span leading edge slats. I think the true reason lies with the
requirements that stall must be demonstrated to me smooth with a
stable pitch forwards and no roll. Now no aircraft is built perfectly
symmetric and if the outer wing stalls you will get wing drop and roll
with pitch down. Thus the designer will in general force the inboard
wing to stall first they by reducing the moment arm and any roll
tendancy. Since Krueger flaps are less efficient they will do this
quite nicely.

Nowadays I believe they change the profile of the slats and tracks to
achieve the same inboard wing stall whilst using the most efficient
high lift device.

Any comments from Boeing aerodynamicists on the above?

ttfn