Spin – Part 1: Why Does It Spin?

Spin accidents don’t happen every day, but when they take place they are almost always deadly. They are deadly because pilots fail to recover. They fail to recover because common logic doesn’t seem to apply in a spin.

Common logic generally feeds a pilot good information that is false … when applied to a spin. Consider the following:

  • When the airplane’s nose is pointed at the horizon, this is a good and normal thing.
  • Wild, fast, rotation is a really bad thing. In a spin, both of those statements are *false*.

In a spin, if the nose is pointed up at the horizon and the turn rate is slow, the aircraft is generally much farther from recovery than when the nose is pointed down toward the ground and rotation speed is very fast.

Spins move faster than most pilots can think and, if the pilot reacts with ‘common’ sense, the results are tragic. The pilot who is caught in a spin by surprise may not remember to act against ‘common’ logic.

To understand the unusual logic that is in effect inside a spin you must really know what makes the airplane spin in the first place. The spin is a stall with two added characteristics: yaw that causes ‘autorotation’ and a downward direction of travel. Let’s take a quick look at the anatomy of a spin to the left:

Autorotation is a self-sustaining reaction arising from different levels of stall affecting each wing. When an airplane spins to the left, it is because the left wing has stalled — it travels down, while the right wing travels up. BUT, recall that both wings are still traveling forward with the motion of the entire airplane, so as the left wing moves down and forward together it changes the relative wind on the left wing.

Relative wind is always opposite to the direction of travel. So when the left wing moves down, the relative wind direction for that wing also moves down and strikes the wing at a greater angle — putting it deeper into stall. At the same time, the right wing is rising and the relative wind present on the right wing also rises. The angle of attack on the right wing becomes smaller and therefore has a greater margin from the stall. If you were to apply right aileron, you would be contributing to the problem. As the left aileron goes down, it would effectively increase the angle of attack on that wing — sending it even deeper into stall.

Translation: The right wing is flying at a shallow angle of attack and the left wing has exceeded its critical angle of attack and has stalled! Both wings are producing less lift, so the aircraft is descending — but left wing has lost all lift while the right has only lost some. The left wing will continuously drop away and the right wing will continue to rise relative to the left wing. Welcome to the spin. Around and round you go … until you figure out how to change those relative wind directions or until you hit the ground!

You can make the left wing stop going down and the right wing stop coming up by applying right rudder (in this left spin). Applying proper rudder reverses the yaw and stops the effects of autorotation. Here’s why: The left wing will come back up and the right wing will come back down. As that happens, both left and right wings will become equally stalled. Things are better, but you’ve still got a problem.

Most normal stall recoveries are completed when the nose is on or slightly below the horizon. But a spin recovery must begin by placing the nose even lower than it already is in a spin. The view out the front window during a spin can be frightening. Push down! Once the stall has been recovered from and smooth air again is passing over the wings you can pull out of the dive with elevator back pressure. It is only natural to want to pull back on the yoke and aim the airplane’s nose back toward the horizon — but this only makes the spin worse.

What about the speed of rotation? It is actually safer to spin very fast than to spin slowly. When the nose is low the airplane will spin faster. You have seen figure skaters go into extremely fast spins on the ice. To achieve the fastest speed they must bring in their arms close to their bodies. They slow down as soon as they open their arms. A nose low spin is a fast spin because the tail follows the airplane down in the same cylinder.

Flat spins are slower because the tail sticks out and widens the arc of rotation like the skater opening up their arms. So a nose low spin has a faster rotation rate, but it is safer, because since the nose is already low it is closer to stall recovery. A nose low spin does not have as far to go to reduce the angle of attack below the critical angle and start normal flight again. A slow, nose high spin might look less scary, but it in fact is worse because the nose must travel even farther down to reach recovery.

BOTTOM LINE: The best thing, of course, is to avoid an unintentional spin altogether. To avoid a spin you must avoid a stall. Most spin accidents are the result of a distraction. No matter what else happens, the pilot must maintain flying speed and not maneuver the aircraft past its critical angle of attack. By doing so, they will avoid a spin. Pilots should consult the information provided by the airplane’s manufacturer about specific stall and spin recovery techniques.

Now that we know why an airplane spins, next week we answer the controversial question: should we teach spins?