Why stall happens from the wingtip in the sweepback plane?

Normally stall begins from the wingroot in the rectangular wing plane.

Why there is difference?

With a swept wing, a portion of the airflow moves spanwise toward the tip. The spanwise flow builds up from root to tip which causes the effective angle of attack to increase toward the tip.

Adding to the previous reply, consider that virtually all swept wings are also tapered - the thinner airfoil section and reduced planform area at the tip both contribute to a higher local stall speed at the tip.


Another large contributor to the stall onset location is the upwash from air flowing around the fuselage from bottom to top (at a positive AOA). In the wing root area, this upwash increases the local AOA substantially, although propwash often mitigates this somewhat in prop aircraft.


Finally, it's worth remembering that most GA aircraft have a few degrees of washout built into the wing, meaning that the the wing is gradually curved (nose-downward) from the root to the tip to mitigate tip stalls and the resulting roll tendencies.

and/or, they have little strips on the leading edge at the wing root which contributes to the wing root stalling before the tips.

Referring only to the first sentence above: While it is true that, all else being equal, an aircraft with a thin wing will have a higher stall speed than an aircraft with a highly cambered wing, the thin wing will have a much higher stalling angle of attack.

For a good reference read "Aerodynamics for Naval Aviators", available for free online reading. Just google the title, and click on the "NAVAIR 00-80T-80" at the FAA.GOV site. Note: This is not an elementary text, and it requires some skull sweat to get thru.

Joe

Yes! (First para).

They gave us Aerodynamics for Naval Aviators to us as AIR FORCE student pilots!! A superb book. No longer handed out at UPT....mine is a treasured copy.