Martin Hepperle's java Prop will show the prop partially stalled at very low airspeeds once a certain pitch is reached. I've certainly seen square props as used in F5B models that are partially stalled on launch they make a god awful howling sound for maybe 10 feet (launched vertically), then go dead silent, and accelerate like mad. The prop is not completely stalled as there is thrust. An airfoil creates lift even if it's stalled, just not efficiently.