Flight Training - December 2011 - 29

In other words, whether making climbing turns right or left at full power, a slight amount of right rudder will be held almost all the time except when rolling left.
LEVEL FLIGHT FORCES. Fortunately, all the

forces we’ve discussed almost disappear in level flight because the engineers have compensated for them in the airframe design, mainly by offsetting vertical surfaces. However, every single time the ailerons are deflected (normally for turns), there will be unbalanced lift on the wings, left and right. This happens even when just fighting turbulence, and especially when rolling into turns. If there is unbalanced lift, there is unbalanced drag, so the wing with the most lift (outside wing in a turn, which has down aileron), will have the most drag, and it will try to lag behind the other one. When it does that, it yaws the nose toward the high wing (outside of turn). So, rudder into the turn is needed, but only when the ailerons are deflected. As soon as the ailerons are neutralized, while in the turn, lift on the wings is balanced (if it wasn’t balanced it would continue to roll), so drag is balanced and no more rudder is needed. When the turn is completed, outside aileron and rudder go in together and the turn is completed.

lot of left rudder will be needed to keep the ball in the center, and a little will be needed the rest of the time. If turning right, without power, the airplane already wants to yaw right from P-factor, so, while the ailerons are deflected, no right rudder is likely to be needed. Then, while in the gliding right turn, a little left rudder may be needed to keep the ball in center.
RUDDER CHANGES WITH ANGLE OF ATTACK. Here’s an important factor that

almost no one talks about: Adverse yaw increases with angle of attack. This is a simple fact of geometry: As the airplane is slowed down, a higher angle of attack is required to maintain level flight. This tilts the lift vector back while the vertical vector that opposes gravity has to be at least long enough to keep the airplane in the air. The result is the drag vector that completes the triangle becomes longer. As the airplane is slowed for approach, and then slowed more for touchdown, the adverse yaw skyrockets.

So, if you’re trying to turn slightly to realign an airplane on the centerline during flare, much more rudder than normal is needed to keep the ball in the center and the nose ahead of the airplane. This is one of the foremost causes of touching down crooked. In most flight regimes, the rudder is there to control yaw, which is another way of saying it is there to keep the ball in the middle (slips notwithstanding). This sounds simple but, in reality, it is one of the most complex, overarching statements in aviation. However, if you master rudder usage, you’ll find that you have flying an airplane licked and you’ll be a smoother, more efficient pilot.
Budd Davisson is an aviation writer/photographer and editor. A CFI since 1967, he teaches about 30 hours a month in is Pitts S2-A Special. Visit his website (www.airbum.com).

Wind direction

RUDDER DURING THE APPROACH. Remember that P-factor on takeoff? Well, it’s still there on landing approach, but in reverse because the nose is down and power reduced. The efficiency of the airplane on approach will be greatly determined by how well the ball is kept centered. That, in turn, is determined by how good of a job we do in canceling out the yaw caused by P-factor at all times during the descent. If it’s a power-on approach, the P-factor’s turning effects will be minimal. However, as soon as the power is brought all the way back, the nose is going to go right and the ball left. The degree of both of these actions will be determined by the size of the propeller in relation to the airplane and whether it is a constant-speed prop. The cure is a little left rudder. Now, however, think about the turns. The nose is trying to go right, so in a gliding left turn, while rolling into the turn, a

APPLY RIGHT RUDDER

Wind direction

COORDINATED FLIGHT

RUDDER MUST BE APPLIED on the ground to keep the nose going straight down the runway. This is because the pedals control the steering, just like the wheel in a car. But soon after takeoff, compensating for wind should be done with a crab angle. Applying only rudder to keep the nose straight would result in a sideslip.

DECEMBER 2011 FLIGHT TRAINING

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Flight Training - December 2011

Table of Contents for the Digital Edition of Flight Training - December 2011