Well, lets see.. .Vertical flight as in the vertical part of a loop, yes, ya are loading the wing and it could be stalled.. .But stright up vertical flight, such as hanging from the prop, the load is on the engine/prop, not the wing. If ya slow to zero and just hang there, the wing could not care less and yer stall speed is not there, well....in theory anyway.. .. .Straight down as well. 0 AOA, no load on the wing, no separation resulting in stall...