We discussed the turning stall in the last SAFEblog and revealed the (often surprising) fact that in coordinated flight, with lift equal on both wings, a stall simply falls away from the lift vector and is very benign. There is only a burble and a drop of the nose, but no rolling or sudden departure from controlled flight that many people expect (and fear). This maneuver is in the private pilot ACS and should be comfortable for every aviation educator. This maneuver not only builds skills and confidence, but also creates a powerful opportunity to promote the need for coordinated flight and the value of correct rudder usage. Since there is no spin tendency in a turn when we are coordinated, this has a super safety value to every pilot; it opens their minds and gets their attention. But we then need a method to achieve better intuitive rudder coordination.
There is lots of confusion about the airplane’s rudder and its function in flight. Remarkably, when Rich Stowell surveyed pilots he found 70% thought the rudder was used to turn the aircraft. This is dramatically wrong and should be a wake-up call to every CFI. Quite simply, the rudder cancels unwanted yaw created by the adverse effect of ailerons, power application, or rapid pitching moments. Most commonly, the downward moving aileron creates yaw, pulling the airplane away from the desired turn direction with “adverse yaw.” This can be *very* pronounced in an older (often tailwheel) aircraft but is largely designed out of modern (control blended) aircraft. That is a nice way of saying modern planes mostly tolerate and disguise “flat-footed flying.” Unfortunately, moving the rudders appropriately and learning coordination is the key to safety and preventing LOC-I.
The critical skill is to anticipate yaw not just reactively cancel it after it has occurred. That’s why the advice “step on the ball” – though correct – is too late and creates more problems than it solves. “Step on the ball” means you already created the yaw problem – slewing the plane – and are subsequently forcing it back into balance with a time-consuming, mechanical input. People who utilize this advice not only have their eyes inside but also fly like bad robots in a jerky and uncomfortable fashion. In addition to being clumsy, we just do not have enough mental bandwidth while flying to be cogitating about “stepping on the ball” (which lags badly anyway). It is essential to tune up our kinesthetic yaw sensing and develop automatic anticipation of adverse forces. This will also makes you an amazingly smooth pilot that your passengers will appreciate.
I recommend all flight instructors (and pilots who want to get sharp) demonstrate (observe) a brisk application of power, aileron, or pitch applied independently at a safe altitude. In each case you will see the nose yaw in reaction to this force applied (physics in action). With practice you can predict which way this will occur (physics!) and discern how much rudder to apply to maintain coordination. I have my primary students initially move the throttle hand and the right rudder together to develop some “muscle memory” while on the ground sitting in the cockpit (works for “chair flying too). This yaw correction will become automatic pretty quickly with directed focus and practice (but is much easier to teach initially than to correct from a bad habit). There is a lot more to this art of learning/teaching rudder and our SAFE CFI-PRO™ workshop has many time-honored CFI tricks to tune up rudder usage.
“As the power increases, you’ll simultaneously press on the right rudder pedal knowing that the entire universe (specifically the airplane’s power induced left turning tendencies) is doing everything possible to yaw the airplane’s nose to the left. But you’ll have none of this nonsense because you are in command of your airplane, right? Right! So step on that right rudder pedal.” Stick and Rudder Mutter, by Rod Machado
But let’s get on to this “cross-controlled bogeyman” we started with. If after we demonstrate that turning stall we ask why the plane did not spin (as expected) in the turn the logical follow up question is “what would cause a stalled plane to spin?” And I guarantee the answer will be “if you stall when you are cross-controlled.” So I demonstrate a stable full slip (power off) and bring the plane to a stall. I love this demonstration, because though the plane is balanced and stable, every pilot anticipates a violent spin entry. In fact with a well rigged trainer, nothing at all happens (except the student finally begins breathing again). Another learning opportunity; why no spin? Because the slip configuration is stable (with no power) with the rudder yaw opposing aileron roll force (perform this only with an experienced instructor and know your plane). This illustrates that the obvious bogeyman is not “cross-controlled” but rather the pro-spin inputs of a skidding turn (ironically the force 70% of pilots think turns the plane) The skid is an excess rate of turn. This usually is created with the rudder but can also be uncompensated force from a go-around attempt (well represented in the NTSB files). The skid is the evil form of “cross-control” and often occurs when people fight yawing force inappropriately with aileron (“driving” again). If there is one aerodynamic principle every pilot must understand this is it; understand thoroughly the difference between a slip and a skid and why one is safe and one will kill you . This is the essence of safety in the pattern. More detail is in this Aviation Safety article I wrote.
Three incidents personally persuaded me to demonstrate these maneuvers and promote this understanding to every pilot. First was repeated flight tests where applicants did not want to “slip to land” because it was “cross-controlled and dangerous.” Then I discovered a website by a respected airline pilot (with great popular following and gravitas) that advised (completely incorrectly) to convert the base to final turn into a slip by applying aileron out of the turn as you lined up on final; “you already have the wing down.” This is of course a skid and very dangerous (pro-spin: do not try this!). The final incident was a young CFI applying for a job at our flight school who demonstrated a massive skid (intending to slip) and confessed he thought you “just cross the controls” to create a slip. This level of confusion is obviously killing pilots and needs to be corrected by every conscientious aviation educator. Again, more here.
Next weekend SAFE will be at the AOPA Fly-In at Frederick, MD (and we would love to meet you there). This blog will cover another misunderstood (and potentially dangerous) aerodynamic force; AOA, CG and pitch (“planes don’t stall, but pilots stall planes”) Fly safely (and often).
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4 thoughts on “Is “Cross-Controlled” Dangerous?”
Well from my understanding, indeed a plane can spin from a slip…. But because of the nature of the forces involved, the lower slide wing must raise up and roll over the top… While in a spin from a skid the lower side wing just ducks under… (Zero correction time)
The slip is okay because, if ever you stall in a slip… You will in all likelihood catch it & correct it when the lower lower starts to raise. The plane depending on the plane might even catch itself
(Lower the nose) before the wing goes over the top.
Oh yes, it absolutely is *possible* to spin “over the top” in a slip, with power off not likely (and yes, you have more time to catch it this departure). Usually this only occurs if a pilot adds power and “energizes” the rudder. Also, tail wheel a/c (they have more rudder authority) are more prone to this tendency. Your plain vanilla Cessna and Piper are docile dogs in a slipping stall.
I read it and I just give me the impression of saying it won’t spin from a slip… When indeed it can, but it takes a lot whole more oppose in a combination of circumstances to have that happen.
Slips are safe, but nothing is fool proof…