Originally Posted by
exeng
I think Rainboe has it. The stab is kept 'in trim' at all times and as such produces a small amount of negative 'lift'. Significant ice may form but that ice will not stall the stab.
Actually, that's rather on the wrong track.
An all moving tail and a fixed tail will both have to generate exactly the same lift to keep the same aircraft in trim (if you were to be comparing a 737 with fixed tail and a 737 with moving tail flying side by side in the same conditions)
To generate the trim force the all moving tail has to do it by changing the angle of attack of the whole tail; the fixed tail does it by changing the camber for a fixed AoA. Generally, the achieve a given trim case the fixed tail will have a lower tailplane AoA as a consequence. Therefore one would usually expect the moving tail to be closer to the stall AoA than the fixed tail. Aircraft will all moving tails certainly can stall the tail; the first BAe Hawk prototype did precisely that when the flaps were deployed on one test flight. Part 25 aircraft are required not to stall the tail, but push them outside the cg envelope in icing conditions and you might find the tail in a stalled condition.
The Viscount accident wasn't strictly a tail stall in the sense that the whole tail stopped generating lift; rather it was a control surface snatch due to flow separation (due to ice) causing huge hinge moments on the (manual) elevator, pulling the elevator to the nose-down position despite crew force application.