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In flight training we're warned against skidding turns since they have a higher potential for a stall/spin (the classic example being the stall/spin on the base to final turn).

However, how does the airplane behave during a stall entered from a slip?

It's a cross-controlled condition, but since the rudder input is opposite to what it would be in a skid, is it more difficult, or not possible, to spin from such a situation?

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    $\begingroup$ A stall could turn into a spin any time you are uncoordinated. $\endgroup$ – Fred Larson Jan 14 '14 at 19:55
  • $\begingroup$ @FredLarson That isn't exactly true.... $\endgroup$ – Lnafziger Jan 14 '14 at 19:56
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In order for a spin to develop, you need two things from the airplane:

  • it must be stalled
  • it must be yawing.

Since the airplane is not yawing while in a slip (it is actually flying straight ahead, although uncoordinated), the airplane simply won't spin. Instead, when the stall occurs the higher wing (which has the higher angle of attack) will stall first, the wing will drop, and the wings will tend level.

That being said, it is still a stall and can be dangerous at low altitudes. It can also turn into a spin if you leave the rudder applied as the wings level and you come out of the slip (and into a skid).

The best protection for all of this is to watch your airspeed and angle of attack to make sure that you always have sufficient airspeed so that you never stall in the first place.

Additional Information

Since this has generated some debate, here is additional information:

Spin

According to Wikipedia (emphasis added by me):

Spins can be entered intentionally or unintentionally, from any flight attitude and from practically any airspeed—all that is required is sufficient yaw rate while an aircraft is stalled.

Yaw

So this brings us to Yaw - Wikipedia:

The yaw axis is defined to be perpendicular to the body of the wings with its origin at the center of gravity and directed towards the bottom of the aircraft. A yaw motion is a movement of the nose of the aircraft from side to side.

Skid

Skid - Wikipedia actually covers this exact scenario:

The skid is more dangerous than the slip if the airplane is close to a stall. In the slip, the raised wing — the left one if the airplane is turning to the right — will stall before the lowered one, and the airplane will reduce the bank angle, which prevents the stall. In the skid, the lowered wing will stall before the raised one, and the airplane will tighten the turn, and the stall can develop to a spin.

Slip

Slip - Wikipedia says:

A slip is an aerodynamic state where an aircraft is moving somewhat sideways as well as forward relative to the oncoming airflow or relative wind. In other words, for a conventional aircraft, the nose will be pointing in the opposite direction to the bank of the wing(s). The aircraft is not in coordinated flight and therefore is flying inefficiently.

Note that the aircraft is moving sideways. The nose of the aircraft is not moving, and it is therefore not yawing. It also says:

Often, if an airplane in a slip is made to stall, it displays very little of the yawing tendency that causes a skidding stall to develop into a spin. A stalling airplane in a slip may do little more than tend to roll into a wings level attitude. In fact, in some airplanes stall characteristics may even be improved.

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  • $\begingroup$ actually, you can develop a spin by using a single item: one wing must be stalled. The ensuing drag imbalance will induce the yaw required and, if not checked, the airplane will/might evolve into a full spin. Slipping turns and slips are both good occasions to stall a single wing, although I agree that getting into a spin from a slip could take quite some work $\endgroup$ – Radu094 Jan 14 '14 at 20:25
  • $\begingroup$ @Radu094 Well, as I said in my answer, if you leave the rudder in after the stall, the slip will turn into a skid and you can then spin the airplane. $\endgroup$ – Lnafziger Jan 14 '14 at 20:37
  • $\begingroup$ In order for an airplane to spin, it must be stalled and in uncoordinated flight. A slip is uncoordinated flight. I think you are confusing ground track and track through the air. Typically a pilot will perform a "forward slip" to counter a crosswind when landing but this straight flight (ground track) is uncoordinated flight - just look at the "ball". So spins from slips are very possible. They are much less likely than spins from skids. The reason is that in a skid, the bottom wing stalls first dropping the plane into a spin, whereas in a skid the top wing stalls first and drops. $\endgroup$ – Skip Miller Jan 14 '14 at 21:08
  • $\begingroup$ (continued) which actually gives the pilot considerably more time to correct and recover. $\endgroup$ – Skip Miller Jan 14 '14 at 21:10
  • $\begingroup$ @SkipMiller I am not contesting the fact that a slip is uncoordinated (I even say that it is in my answer). However, you are not yawing when in a slip. Yaw: A yaw motion is a movement of the nose of the aircraft from side to side." In a slip, the nose of the aircraft is not moving at all: It is steady and is not yawing. In fact, you are affecting the ground track (which is why you do it to counteract the wind). If you feel that you can provide a better answer, feel free to add your own though, that's the premise of our whole system here! :-) $\endgroup$ – Lnafziger Jan 14 '14 at 21:42
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You are indeed yawing in a coordinated turn, yes or no?

If you stall in a coordinated turn, will you enter a spin? I'll answer that one: No. My CFI and I spent a few hours exploring accelerated stalls, both straight and turning. This is not a spin entry maneuver.

So the original statement you made that two things are necessary for a spin: stalled and yawing, is not completely correct. It is stalled and uncoordinated. I don't think this is just a nit we are picking. Having said that, spins out of slips are rare. In an aggressive slip, the nose can blank the airflow over one wing and if the pilot doesn't react immediately and appropriately, you are in a spin. I discount the logic that a badly executed slip turns into a skid turns into a stall. While possibly true aerodynamically, the purpose of our training is to prevent unintentional spins, and you can indeed get into a spin from a slip. Your statement that you can't spin from a slip is just not helpful to the majority of pilots who are basically just in search of the Hundred Dollar Hamburger.

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  • $\begingroup$ Sorry Skip, but you do need both of those to enter a spin, and in a coordinated turn you are indeed correct that it won't spin, but that is because it isn't yawing. $\endgroup$ – Lnafziger Jan 15 '14 at 16:25
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    $\begingroup$ I've been quiet for a while because I recognize the possiblity that I have a less than complete understanding of this. But this has been gnawing at me so please educate me. You are engaged in a full rudder slip. Now you relax a bit the rudder pressure, and you are still in a slip but now the nose is moving across the horizon. Is that a yaw? Now you stall. If what you say is true, the plane will not enter a spin because you are in a slip. Please explain why not? And thanks for your patience. $\endgroup$ – Skip Miller Jan 21 '14 at 22:00
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    $\begingroup$ So what you describe there could indeed turn into a spin because if the nose starts to move across the horizon, you have started to yaw (aka skid). You would have transitioned from a slip to a skid because you only "relaxed a bit of rudder pressure" instead of maintaining the zero yaw condition (slip) that you were in before. In my answer above I say "It can also turn into a spin if you leave the rudder applied as the wings level and you come out of the slip (and into a skid)." $\endgroup$ – Lnafziger Jan 21 '14 at 22:09
  • $\begingroup$ I am a Full Time CFII for 10 years now with 8000 flight hours. You are infact correct. But you already know that. I don't understand why lnafziger does not think you are correct. he was saying that if the airplane is stalled and yawing you will spin. Obviously thats incorrect. He doesn't recognize that you are infact yawing while turning. But that doesn't mean you are uncoordinated while doing so. The simple answer as you stated earlier and i'll say it again is it takes two things to spin: A stall and Un-Coordinated flight. Simple as that. $\endgroup$ – Michael Spencer Dec 22 '16 at 17:07

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