License to Learn

Stall commandments

November 1, 2010

Are you nervous about stall practice? You have copious company. One student I inherited from another instructor became so nervous during the stall sequence that he developed a peculiar habit of humming along with the stall horn. I’m not kidding. This airplane had a two-tone stall horn and he’d hum right along, changing pitch with the horn. During the stall, his tunnel vision was so intense that you could put a moving finger up to his lips and have him make the “boo, boo, boo” sound that’s perfectly normal—for an infant.

Why do some pilots get nervous when the wings of their airplane go on an aerodynamic strike? One word: predictability. Specifically—the lack of it. If an airplane stalled and always pitched only forward along a plane perpendicular to the lateral axis of the airplane (from the student’s nose to his feet), then stalls would be a ball, and most people’s discomfort would be tamed. The problem is that during the stall one wing can reach its critical angle of attack before the other. Once that happens, the airplane begins to yaw and roll in the direction of the most stalled wing. You know where that can lead, right? I’m talking about the “cardinal spin” of aviation—the unanticipated spin.

Here are the two stall commandments you need to know to make stalls more predictable and much more fun:

Stall commandment number one: Thou shalt not stall an airplane in uncoordinated flight. To some this may be a revelation, but it’s actually sound stall theory and one of the most important rules about making stalls more predictable. It’s also the single biggest reason you always want to fly coordinated.

When an airplane approaches the stall with the inclinometer’s ball displaced even slightly, one wing may have a slightly larger angle of attack than the other. The result? One wing stalls before the other, and the airplane begins to yaw and roll in the direction of that wing. Why does this happen? Imagine you’re in a skidding left turn, meaning that the nose points inside the turn and the ball deflects to the outside of the turn (think too much left rudder for the bank angle used). Excessive left rudder yaws the airplane’s nose to the left, resulting in the left wing moving rearward (the wing slows down slightly) and downward (increasing its angle of attack slightly). The result is that the left wing stalls first in the left skidding turn. Had you been on the ball and kept it centered, both wings would stall simultaneously, and the airplane would pitch from your nose to your toes. Unless you are a professional prizefighter, that means the airplane will pitch straight ahead of you in a very predictable manner. No yaw and roll. Recovery from this type of stall is easy—reduce the angle of attack by releasing elevator backpressure and apply maximum allowable power to help further reduce the angle of attack and minimize altitude loss.

Now what happens if you have happy feet and accidentally stall an airplane in uncoordinated flight? Your stall becomes a hummer and a bummer. It’s time to follow the second stall commandment.

Stall commandment number two: Thou shalt not lift a falling wing with thy ailerons, but instead thou shalt simultaneously reduce the angle of attack and stop the yawing motion with rudder.

That’s right. If you stall an airplane in uncoordinated flight, it’s likely that your nose (actually, the one on the airplane) will begin to yaw at the moment of stall. You may be in a tizzy, but you’re not yet in a spin, so you don’t apply full spin recovery technique (more on this momentarily). You’re in a normal stall with one wing stalling a bit more than the other. That’s why you’re yawing (and perhaps hearing a slight hum in your headset).

Reduce the angle of attack and simultaneously stop the yaw by applying rudder in the direction opposite the yaw (whatever you do, don’t lift the falling wing with the aileron until you’re sure it’s no longer stalled). How much rudder do you use? Push the pedal to the metal until the yaw stops. You aren’t going to hurt the rudder. Your rudders don’t have feelings. Keep in mind that your rudder is the last flight control forfeited in the stall. That means it works well during the stall, mainly because it’s poking up behind the airplane into the free airstream. If the airplane doesn’t yaw it won’t spin. Period.

Of course, if you dilly instead of dally, and let the airplane enter a full spin, then you’ll want to do what my friend and spin expert Rich Stowell recommends in his ultimate stall book, Stall/Spin Awareness. You’d use the PARE technique—reduce Power, neutralize the Ailerons, apply opposite Rudder to stop the yaw, and then use the Elevator to break the stall (but don’t break anything else, even if it’s a rental). Do you see the pattern here? It’s your rudder that either stops the yaw before the spin, or stops it in the spin. Rudders rule.

So there you have a low-hum, two-commandment plan of action that allows you to have a ball with stalls. But do try and keep that ball centered.

Longtime CFI Rod Machado has recently published his newest instruction manual. Visit the author’s blog.

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Rod Machado will be a featured speaker at AOPA Aviation Summit 2010 in Long Beach, California. He will offer three different forums this year. He is also a co-host for a “Dine Around” event on Thursday, November 11. For more information, visit the website.