[Ref. The Pilot’s Manual PM2 Ground School Page 23,84]

Washout – decrease AOI(Angle of Incidence) from wing root to tip.

Washout imply wing root would reaches stall angle prior to the wing tip, thus wing root would stall first

Notes: rectangular wing also tends to stall at wing root first.

 

Benefit of wing root stalling first

1. allow the control buffer over the horizontal stabilizer
2. the ailerons should still be effective  – even in case asymmetric stall (i.e stall occurring on one wing before the other)

 

NOTES:

AOI – angle between Chord line and Longitudinal;

AOA – angle between Chord line and RAF

 

Sweepback and Taper wing – Stalling at the wing tip first