Lesson 3: Power Off Stalls

Okay, my lesson yesterday was on power off stalls. People without a lot of aviation knowledge hear "stall" and have visions of airplanes falling from the sky. It's really nothing like that, and is a very mild event. It occurs when the wing exceeds its critical angle of attack, the angle at which the wing loses lift and air stops flowing smoothly over it.

Stall recovery is generally pretty easy. You simply lower the angle of attack (typically by lowering the pitch of the airplane) and/or add power to increase airspeed. You also need to make sure the plane stays level and does not roll off onto one wing (which is the entry into a spin, which is generally not a good thing unless you are doing aerobatics or otherwise intentionally spinning the airplane).

In the Zodiac the spins are pretty much a non-event. As you lower the speed you have to pitch the nose up a bit to maintain altitude. With the flaps down the stall warning horn starts to make noise at about 50 knots, but the stall doesn't actually occur until about 38 knots. So there is plenty of time to know it's coming. The stall does not break sharply in the Zodiac; instead the plane just starts to mush, with the controls getting soft and movements needed to make changes get exaggerated. At the same time the vertical speed picks up, and even though you are level, you are sinking quite rapidly (500-1000 feet per minute).

Recovery is done by simply letting the nose come down (it wants to anyway) and adding power. The plane flies itself out of the stall almost instantly. The plane WANTS to fly. So that's it, power off stalls. Power on stalls will come later, and occur without reducing to power or lowering the flaps, instead using pitch to raise the angle of attack to the critical point.