What’s with the rudder pedals?

So many times I return from a course and ask my wife (a non-pilot) – “guess what the pilot did?”. And she’ll knowingly reply “the pilot used the ailerons for what the rudder pedals are to be used for”.

Yes, again – so many times – yes!

In the late 1800’s people were using elevators and rudders to control pitch/altitude and rudders for turns in their gliders. It was Wilbur and Orville Wright who came up with the addition of banking the aircraft by wing warping. These three controls made the Wright Flyers very controllable and therefore very successful. One design that Wilbur and Orville built had the rudders and wing warping interconnected so that when one flight control was deflected in one direction, the other also moved in the direction of turn. This reduced their loss of control incidents tremendously. BUT, they found that at times it was preferable that these flight controls do not move in the same direction every time they were moved.

 So, when are the times that we need the rudder and the ailerons to move in opposite directions? Maybe two better questions are 1) what are the aileron’s to be used for and 2) what happens when they are used?

Ailerons are to be used to help keep the aircraft from drifting downwind during a crosswind takeoff or crosswind landing. Of course, if too much aileron is used for the nose of the aircraft will tend to turn into the wind. What happens when they are used in flight? Ailerons are also used to provide the bank for a turn. The aircraft begins a bank in the correct direction but the aileron that moves downward produces lift and more drag than the upward deflecting aileron causing the aircraft to yaw in the opposite direction slightly.

What does the rudder do in flight? First we should ask what a yaw damper does in flight. It dampens the yawing caused by turbulence and coordinates the flight controls when the ailerons are deflected to enter or roll out of a turn. If the aircraft has no yaw damper the pilot should provide these inputs.

Now what about landing with a crosswind? The pilot should approach the runway in a crab and sometime before touchdown should align the longitudinal axis of the airplane with the centerline of the runway. While straightening out the airplane with the centerline the aircraft will begin to drift downwind. This drifting is to be corrected by use of the ailerons. Crosswind landings are difficult for several reasons. I believe that landing in a gusting crosswind is the most difficult maneuver I’ve had to accomplish while flying – with one exception. The Aerostar is a pretty easy airplane to land in a crosswind, even if it is a gusting crosswind.

Why is a crosswind landing difficult?

  • As you become cross controlled (where the ailerons and rudder are moved in opposite directions i,e, the aircraft is uncoordinated) as pressure is applied to the downwind rudder pedal, the aileron needs to be moved in the opposite direction. As the aileron is applied to prevent the aircraft from drifting, this causes the additional rudder pressure to be applied to keep the longitudinal axis lined up with the centerline.
  • During some strong crosswind landings, the upwind main gear tire will contact the runway first, then the other main gear tire, and finally the nose gear tire. This is a challenging maneuver. For awhile the aircraft is somewhere between flying and taxiing.
  • On many aircraft, when the rudder pedal is pushed, the nose gear moves in the same direction so that when the nose gear wheel touches down it tends to steer the aircraft to the downwind side of the runway – sometimes pretty aggressively. Numerous aircraft have ended up off the runway during a crosswind landing procedure.
  • Gusty conditions. Gusty conditions means that the aircraft’s longitudinal axis will not be lined up with the centerline for very long periods of time. Gusty winds, trees or buildings blocking the wind at times during the landing phase make it so the pilot needs to keep adjusting the flight controls throughout the last portion of the final leg and the flare. Even after all three wheels are on the ground the wind still has an effect on the aircraft – especially high wing and lightweight aircraft so that the control yoke should be rotated in the direction of the wind more and more as the aircraft slows due to the ailerons becoming less effective at the slower speeds.

So, why do pilots stop using the rudders for yawing? Some of it is that in many airplanes pilots find that they can make a banked turn and barely be uncoordinated without using the rudder pedals to roll into or roll out of a turn so they give up using the rudders. Some fly aircraft with the yaw damper on throughout the flight and the yaw damper does at least as good a job in dampening yaw from turbulence as the pilot does so these pilots begin to leave their feet flat on the floor throughout a flight. Some aircraft like the tip tanked twin Cessna series actually start to roll shortly after yawing begins and this causes the pilot to think that he needs to correct this with aileron. Those who fly these aircraft should try correcting this yawing/rolling motion with ailerons and see how well this works, then use the rudder pedals and see how quickly the yawing/rolling motion stops.

Feel free to e-mail me with your thoughts on this post. I’m sure it could presented in a better manner. Also, take a look at the crosswind landing video this website has downloaded from YouTube – quite interesting. Could you handle these crosswinds?