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In flight training, you're always told not to cross-control, (for example, rolling right aileron, and stepping on the left rudder), but it seems to me that is exactly what a slip is doing.

Is it that a slip is intentional, and a cross-controlled situation is typically unintentional?

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You are right: A slip is a cross-controlled (and uncoordinated) situation. It's exactly what your instructor was teaching you to avoid during your early lessons.

As far as nomenclature goes: all slips are cross-controlled maneuvers, but not all cross-controlled maneuvers are slips: On climb-out in most piston singles you will be stomping on the right rudder to offset the plane's left-turning tendencies, and you will probably notice that you're rolling in a tiny bit of left aileron (which offsets the banking tendency introduced by the rudder) - your controls may be very slightly crossed, but the result is coordinated flight (a centered ball).


The real difference here between an "unintentionally cross-controlled situation" and an "intentional slip" is the intentional bit: When you are knowingly slipping the aircraft - for example to bleed off altitude on a high final without increasing your airspeed - you're aware that you're flying in an uncoordinated and aerodynamically unstable condition. You're aware of the risks, and are hopefully monitoring the aircraft carefully to avoid a stall/spin.

For a little more insight, faaflighttest.us has a reprint/copy of an Aviation Safety article from April 2006 which is worth a read, and possibly an hour in the air practicing some of what they discuss with your instructor so you can get the "feel".

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    $\begingroup$ One other point is that a slip is done with sufficient airspeed that it won't create a problem, other than the (desirable) loss of performance that it causes. Where being cross controlled really becomes an issue is when you are getting close to your stall speed! $\endgroup$ – Lnafziger Dec 27 '13 at 23:28
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    $\begingroup$ Its also worth mentioning that in some aicraft the preferred crosswind approach is a cross-controlled maneuver called wing down, top rudder. For example, if the wind is blowing right to left, tye right wing is dropped to counter the drift, and then left rudder is applied to maintain RoD and centerline. $\endgroup$ – Rhino Driver Dec 10 '14 at 20:32
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    $\begingroup$ @Lnafziger most airspeed indicators don't provide correct indication in a fully cross-controlled slip, so don't look at the ASI (which will be too loow). Instead, the important thing is to keep the nose well below the horizon. $\endgroup$ – rbp Mar 22 '15 at 22:14
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"you're always told not to cross-control"

This should not be what you're taught. You should fly in coordinated flight, and that can often mean being cross-controlled.

Two very common examples of coordinated, cross-controlled flight are left hand turns on take off and steep turns.

Because of p-factor, on departure, you will have some amount of right pedal in, but to turn left (particularly in a nosewheel airplane), you need left aileron while you still have right pedal in, and its not unusual for full-power climbing left turns to have left aileron and right pedal in coordinated flight. You'll see this more in a high-performance airplane.

The second example is steep turns. After you roll into a steep turn to the left, say, the over-banking tendency will require right aileron with left pedal to keep the plane from increasing bank angle, in coordinated flight. The over-banking tendency is less pronounced below 45 degrees of bank in low aspect-ratio aircraft, like your typical Cessna.

So the rule is not "don't cross-control," but rather "fly coordinated"

That being said, the easiest way to get a plane into a spin is full cross control, and pull back on the stick. That's probably why you're taught never to do it.

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  • $\begingroup$ Great answer! I will change the way I talk about this. "Coordinated flight" is a great keyword and the better way to talk about it. $\endgroup$ – Canuk Apr 12 '15 at 5:52
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When you are doing a forward slip for example to bleed off altitude without increasing airspeed, you are purposefully uncoordinating the plane. That is the entire purpose of a forward slip in that particular situation; the reason it is useful is because you are intentionally increasing the surface area of the plane that has to push it's way through the air/relative wind while still maintaining the ability to descend in a controlled manner. This is why I don't prefer rules that are very general; Your rules at the time should be based on your desired outcome. That isn't going to be the same in every situation... Although I'm speaking very generally here :p Rather than have a set of one size fits all rules, I think it is better to keep keen situational awareness and have a set of rules for different circumstances. very rarely do I enjoy a rule that says "never do this" or "always do this" save for "always be prepared and plan accordingly when possible".

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