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.") It's part of what makes aviation so exciting for all of us... just when you think you've seen it all, along comes a scenario you've never imagined.

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Aero-Tips 03.18.06

Add power and you need right rudder to track a straight line. Raise the nose to climb and you need right rudder to maintain coordinated flight. Why specifically do you need right rudder? Are there any times when left rudder is required to track a straight line?

Feel the Force

What’s correctly called the "left-turning tendency" of propeller-driven airplanes stems from four interrelated forces:

1. Torque reaction. For every action there’s an equal and opposite reaction. As internal engine parts and the propeller rotate one direction, the airplane tends to roll the other. Many airplanes have engines mounted slightly off center to help compensate.
2. Corkscrew effect. Air off the propeller corkscrews around the fuselage and, in most designs, impacts the left side of the vertical stabilizer, pushing it right and the airplane’s nose left.
3. Gyroscopic loading. A rotating propeller is like a gyroscope. Spinning gyros exert force at 90? to the plane of rotation, which in airplanes means a yaw to the left.
4. P-factor. Asymmetric loading of the propeller means more thrust is created on the down-moving, right propeller blade. This added force drives the airplane’s nose to the left.

Adding power increases all four factors. Raising the nose increases factors (3) and (4). Add power and raise the nose at the same time, like in a go-around or missed approach, and it’ll take careful rudder control to avoid turning to the left.

Left Rudder?

Are there times when it takes left rudder for coordinated flight? Sure. Reduce power to idle, or put the nose of the airplane down, and it’ll take left rudder to keep the turn coordinator’s ball centered. This is obvious in a Cessna 172 in a descent, or any airplane practicing Lazy 8s. Another case when left rudder is required for coordination is when the airplane out of rig, not terribly unusual as the fleet ages.

And of course, if the engine and propeller rotates the other way, as in most European-designed engines like that in an Australian friend’s Tiger Moth biplane, all the factors drive the airplane’s nose to the right, requiring left rudder for coordination.

Aero-tip of the day: Do what it takes to keep the ball in the center, but you can usually predict which foot will have to do most of the work.

FMI: Aero-Tips