Physiology, Head Position, and Aiming Reference

One major difference between piloting a plane and driving a car is that the car generally travels in the direction that the driver points it, where an airplane can and often does travel in a different direction than it is pointed.

When a plane’s direction of travel is different from the direction it is “aimed” it is in a “crab” or is moving sideways as well as forward.

Often, the crab is intentional, and sometimes quite harmless, however during landing, at the point of “touchdown”, if the plane is not aimed in the same direction as it is traveling, there will be a significant and often dangerous side loading of the landing gear, and sometime a loss of directional control.

One common experience is the typical tricycle gear trainer, where the student is sitting in the left seat and incorrectly lines the plane up with the runway using the center of the cowl or propeller. As is shown in the figure below, the pilot’s perception is incorrect and in fact, the plane is crabbed to the left.  (Solution---change the reference aiming point to one to the left of the propeller an equal amount as the pilot’s head is to the left of the center of the plane. )  The CFI will likely be telling the student to indut “more right rudder” and the student will be a bit perplexed thinking he is aiming correctly

A similar problem can occur in tail wheel planes with centerline seating. Most common in this case is a student who “leans right” and whose head is positioned to the right of the plane’s centerline. As shown in the figure below, the plane is crabbed to the right.

In the side by side seating tricycle gear plane—it is impractical for the pilot to move his head to the center of the plane, but in the tail wheel plane—that is the most common “correction”.  Hence, pilots that “lean right” will often hear the CFI barking “sit up straight—quite leaning right”.  (By the way—since the student who leans right will always sense the plane is more left than actual, he will often make inputs to rudder and aileron to move the plane to the right.)

This issue is also present if one focuses on "ten and two" rather than just the "gun sight" focus on the centerline. 

The situation is complicated when/if the student suffers from a relatively common condition called “scoliosis” or curvature of the spine. The figure below shows a curvature that leads to a lower right shoulder.

This condition is present to some degree in millions of people. As most men realize when a tailor adjusts their suit, our bodies are not symmetrical—one arm is usually longer than the other and one leg is usually shorter than the other.

Scoliosis develops normally during puberty and tends to get a bit worse in old age. If the person tries to lower the one shoulder to level out his frame, often there is discomfort.  Especially for more senior men whose spinal discs have normal age related degeneration. Hence, people with scoliosis tend to “adapt” to functioning with their body leaning toward the lower shoulder, causing the head to be a bit off center.

Two of my CFI’s were obviously attempting to “correct” my tendency to lean right, leading to a great amount of frustration.

Upon reflection, I performed the following analysis. (The engineer in my could not resist the "analysis" of this "problem". ) First a picture of me standing straight in front of a mirror. Since I am taking a photo of my mirror image, right and left are reversed—note my wedding ring on my left hand.

You will note my right shoulder is one inch lower than my right, even though I am otherwise standing erect.

 Now, complicate that with the position of the pilots hands on a typical tail wheel plane with stick in right hand and throttle in left.

Some pilots will place their hand on the throttle, but keep their elbow low to reduce the “tilt” but many pilots will rest their forearm on the window sill, raising their left shoulder. Both pilots above are leaning right. (As is the pilot in the next photo.)

The issue can be exaggerated in a Cub vs a Champ in that the Cub's throttle is a bit higher and further rearward than the Champ's.

  

The first picture is me. The other two are very skilled, high time "famous" tail wheel pilots. The photos are captures from their Youtube videos.

There are two ways to compensate for this—move your head, tilt your seat, or change your reference. Changing the reference to a point on the cowl to the right of center to match the amount your head is leaning right is similar to what the left seat pilot has to do in the tricycle gear plane.

Obviously, moving your head to be perfectly aligned with the centerline of the plane is the most ideal—like aiming a rifle with open sights---but those that use a rifle scope know that the scope is offset from the barrel and allows accuracy simply by insuring that the aiming line is perfectly parallel with the barrel.

So, if you are most comfortable “leaning” a bit, simply “adapt” to flying the plane by making a small adjustment to your reference point/s and “sight picture”.