wing tip stall
what union, what are you saying?
'when you put flap down you are changing Cl over that part of the wing the flaps affect. you have in fact two different wings on the a/c.an inboard high lift section and an otboard standard section. on a cessna you have two other high lift considerations the slots above the flaps nd the sheer size of the flap in relation to wing area. what this results in is an inboard wing section that will remain unstalled with a normal approach into the stall. there will be a wing drop because the tip must stall first,whichever one goes first goes first. the large wing drop is due to the very large change in Cl across the breadth of the wing coupled to the unstalling of opposite tip.'
When lowering flap you increase the Aof A of that section of the wing. The wing tip is unchanged by this action. The wing root will, therefore, stall at an earlier stage when the a/c pitch is increased further and even sooner than the wing tip in this condition than when the wing is clean. The a/c is of cause less laterally stable with flap lowered. There is no vortice control to the edges of flap unlike a wing tip. The outflow will become turbulent. On lowering aileron you must also increase the angle of attack of the wing tip. The combination of lowering aileron together with turbulent airflow must cause a likelyhood of an unwanted wing tip stall.
The advice comes to mind, "engage brain before opening mouth"