On a delta wing, the upper surface vortices break up naturally at high angle of attack, and a lift drop is observed on the parts of the wing affected by this phenomenon. This break-up may jeopardize the aircraft longitudinal stability (appearance of vibrations, buffeting), in particular at angles of attack higher than normally used for landing.

This visualization in the water tunnel was quite similar to that observed by NASA during flight tests.

Image created by Henri Werlé. Reproduced with permission from his spectacular collection Courants et Couleurs published in 1974 by ONERA, the French Aerospace Lab.