Aero-Tips!

A good pilot is always learning -- how many times have you heard this old standard throughout your flying career? There is no truer statement in all of flying (well, with the possible exception of "there are no old, bold pilots.")

Aero-News has called upon the expertise of Thomas P. Turner, master CFI and all-around-good-guy, to bring our readers -- and us -- daily tips to improve our skills as aviators. Some of them, you may have heard before... but for each of us, there will also be something we might never have considered before, or something that didn't "stick" the way it should have the first time we memorized it for the practical test.

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Aero-Tips 06.25.06

Trim your airplane for level flight in smooth air. Take your feet off the rudder pedals, then move the controls to bank the wings (left or right). Watch carefully to where the airplane's nose points. In many designs the nose will swing in the direction opposite wing bank. You've just seen the effect of adverse yaw.

Adverse yaw results from the drag of deflected ailerons. Say you move the controls to the right-the right aileron goes up, and the left aileron goes down. The "spoiler" effect of the raised right aileron reduces lift on that side and banks the wing to the right, but the lowered left aileron creates more drag that tends to resist the turn. The draggier the aileron (based on airplane type) the more pronounced the resulting yaw away from the direction of turn.

In some airplanes -- especially antique, tailwheel types -- there may be so much "aileron drag" that you can steer the airplane on the ground using adverse yaw. This can actually be helpful taxiing, taking off and landing in a crosswind.

Overcoming adverse yaw

Of course properly using the rudder overcomes this effect, by moving the airplane's nose back in the direction of the turn. The amount of rudder deflection needed will vary with the airspeed, power setting and the specific airplane type -- part of the fun of checking out in a new type of airplane is learning how to maintain perfect rudder coordination.

There are a couple of design philosophies that help minimize adverse yaw:

• Frise ailerons are hinged so that the leading edge of an upward-deflected aileron extends downward beneath the wing. This creates drag on the up-aileron to counter that created by the down-aileron. The tradeoff: more total drag, causing reduced airplane performance.
• Differential ailerons are rigged so ailerons do not deflect downward as far as they do upward. There's less drag created by the down-aileron, so less adverse yaw results. Drawback: reduced aileron effectiveness and lower roll rate.
• Aileron/rudder interconnects in some airplanes couple the aileron and rudder controls so a movement of one creates a movement of the other. Bank the airplane with ailerons and the rudder will displace enough to compensate for adverse yaw. Shortcomings: the effect is precise through a small range of airspeeds, power settings and bank angles. These interconnects also encourage "feet on the floor" flying, leading to sloppiness in flight regimes needing active rudder input and when the interconnect-acclimatized pilot flies an airplane requiring more rudder control.

Aero-tip of the day: Actively use whatever rudder input is necessary to overcome adverse yaw.

FMI: Aero-Tips