SKIDS

Skidding turns are one of the most dangerous things a pilot can do in an aircraft. Skidding turns lead to spins and low level spins lead to death or at the very least a lot of “hurt.” Now with that said as an opening to this article let’s discuss skids. First off exactly what is a skid? A skid is an uncoordinated maneuver. But then again so is a slip. So we need a more exact definition. Let’s try this one. A skid is an uncoordinated maneuver occurring when the pilot uses too much rudder input in the direction of the turn. Another way to say that is the pilot uses too much “bottom rudder.” Now we have defined a skid so that it is easy to tell the difference between a skid and a slip. That is, if we know what a slip is. Let’s use this as a definition of a slip. A slip is an uncoordinated maneuver occurring when the pilot uses too much rudder input opposite the direction of the turn or too much “top rudder.” Both slips and skids need to be understood as rudder input issues not as either too much or too little aileron input. The amount of aileron input determines the amount of rudder required for coordinated flight. The converse of this statement is all wrong. That is, it is not true that the amount of rudder input determines the amount of aileron needed. That’s a “cart before the horse” concept and is a totally inaccurate way to think. The ailerons are used to determine where we are going: straight, left, right. The rudder is there to offset adverse yaw caused by the ailerons being moved.

One comment if I may. Occasionally I hear pilots state that they lead a turn with the rudder. It is not possible to input rudder before any aileron movement and stay coordinated. That is, you cannot offset adverse yaw if it has not happened yet. What I think those pilots mean is that they input rudder (and maybe a lot of rudder) at the same time that they move the stick in the direction of the turn. But certainly you cannot correct something that has not yet happened.

Now back to skids. Student pilots (and sometimes non student pilots) tend to skid their turns. And they are more apt to skid the turns when they are in the latter portion of the traffic pattern. This is because they are now low enough to be aware of the ground and they also know that they want to align the sailplane with some ground reference. For example, on the base leg they want to be perpendicular to the runway. Also, as they roll out of their turn from base to final they want to be aligned with the runway. And this is where the problem comes in. I want to turn but I see that I’m not turning fast enough. I am going to overshoot my turn. What could seem more “natural” than to try to point the nose where I want to go? Step on the “bottom rudder” and push the nose around and “help” the turn go faster so that the sailplane is pointed in the right direction. Seems reasonable. But it is not. It is all wrong. I have just entered a skidding turn by pushing on too much “bottom rudder.” As instructors we must teach that if you want to turn faster the only way to do it is to increase the bank angle.

We now know what skids are and when and where they are most likely to occur. But why are they dangerous? Slips and skids appear to be very similar. It can seem to the student that one is just uncoordinated flight in one direction and the other is uncoordinated flight in the other direction. So what is the big difference? Why are skids so dangerous yet students are taught to do slips? This is where we must look at what happens when the pilot pushes too much “bottom rudder.” Picture a sailplane in a somewhat shallow left bank because this is when a skid will most likely occur. If we were in a steep left bank there would be little need to help the plane around the turn as it would be turning quickly already. Now we’re in a shallow left bank. We want to turn faster, and so we start pushing too much on the “bottom rudder.” The tail of the sailplane moves to the right. The right wing actually speeds up. The left slows down. Additionally, the fuselage starts to block the airflow to the left wing area closest to the fuselage. So we have the left wing slowing down and also the inner portion of the wing is not getting a good airflow. This situation greatly increases the indicated airspeed at which the left wing will stall. If indeed the left wing stalls, then it drops. The right wing is still happily flying and flies right “over the top” and we are very quickly in a spin. Any time you hear about a stall/spin accident in the traffic pattern you can bet your bottom dollar that a skidding turn along with slow airspeed were the cause. For those who have had spin training you know that the way most instructors teach spin entry is to slow down, put one wing slightly down and push full “bottom rudder.” Sounds just like a big skid and indeed it is.

Finally let’s look at a slip and see why it is not so prone to cause a spin. Again picture the sailplane is a shallow left turn. Now push on the “top rudder.” The tail moves to the left. The top (right) wing slows down. The bottom (left) wing speeds up. The fuselage starts to block a portion of the top (right) wing. All of this actually causes a self-correcting process that must be offset to stay in a slip. The bottom wing gets more lift as it is going faster. The top wing gets less lift as it is slowing down and has a portion of its wing closest to the fuselage not getting good airflow. This means that if no other pilot inputs are made the left wing comes up, the right wing goes down and the sailplane comes out of the bank. That is, there is no quick tendency for the sailplane to go into a spin. Don’t get me wrong. You can still get yourself in trouble with a slip if you do not enter and exit the slip correctly. However, the slip can be a good tool to use for either correcting for crosswinds or for increasing your rate of descent without gaining airspeed. It should also be noted that to the student slips do not seem “natural.” Students are not inclined to want to point the nose of the sailplane away from the direction of the turn so they are much less likely to unintentionally slip in the traffic pattern.

On the lighter side I’ll tell you that when I was learning to fly I was so bad in the traffic pattern at trying to push the nose around with the rudder that my instructor told me I should start every turn in a slip. That way when I tried to “rudder” the plane around the turn I would simply move to coordinated flight or at least pass through it on my way to a skidding turn. Seriously, work very hard at avoiding skidding turns especially in the traffic pattern. Keep the string straight! Remember that if you need to turn faster the only correct way is to bank steeper.

Fly Safely and Have FUN!!

Frank Reid