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Preventing Tip-stall on Swept Wings (Part 1)

Something can be done to modify the stall pattern of rearward swept wings, such that they pitch down at the stall (ie: display positive longitudinal stability).


This is where the incidence angle at the tips is less than that at the wing root. A gradual torsional twist in the wing is the result. The tips no longer reach their stall angle of attack, until other more inboard sections of the wing do so. Twisting the wing downwards at the tip has a limit to it, as too much washout may see the outboard section of the wing provide zero lift, or negative lift at small overall A of A’s, such as when in the cruise. Refer fig Lift 3.


Leading edge slat deployment

Another method of attacking the problem of early tip stalling is to have the outboard sections of the leading edge devices (LED’s), extend automatically when within certain A of A/airspeed values. This re-energises the the flow over the top surface of the wing immediately aft of them, delaying break-up of streamline flow there until more inboard areas have stalled. It also improves outboard aileron effectiveness near the stall.

Fig Lift 3. Washout (exaggerated)

Wing fences

These inhibit the flow of air outward toward the tips, which is called “spanwise flow”. This tends to happen at high A of A’s and is quite pronounced in swept designs. Spanwise flow is a factor in producing tip stalling. Effectively, wing fences split the wing into two sections, inboard of the fence, and outboard of it, isolating the effects of each part from the other.

They assist in preventing spanwise thickening of the boundary layer. At the fence a trailing vortex is produced that rotates in the opposite direction to usual wing tip trailing vortex. The vortex produced by the fence scours away the local boundary layer. Refer fig Lift 4.

The above briefing is a sample from the ATPL Aerodynamics and Systems course, which will soon be available via Internet. I hope you found this of value.

Fig Lift 4.Wing fences.

Ways of solving wing tip stalling is a typical ATPL, and airline technical interview question.

Another free ATPL training editorial will discuss other ways to prevent tip stalling.

Best wishes

Rob Avery

ATPL Lecturer

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Marty says ... "Goodbye to GA".

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