By Leslie Caubble, CFI/IGI
“Step on the ball!”
“Stay coordinated!”
“More right rudder!!”
It’s a rite of passage for pilots-in-training to hear these words come from their flight instructor repeatedly. The airplane rudder is one of the most misunderstood of the primary flight controls. Yet the rudder is one of the most important and one of the most under-utilized.
The rudder’s most important function is controlling the yaw of the aircraft, which moves the nose of the plane left and right. The yaw of the airplane rotates around its vertical axis. The pilot can control the yawing of the plane by inputs on the rudder pedals. Before we get into some scenarios when rudder use is important, let’s dig deeper into what the rudder is.
Where is the rudder?
The rudder is a movable flight control which is mounted on the trailing edge of the vertical stabilizer on the back of the airplane. Some new student pilots think the rudder and vertical stabilizer are the same thing. The vertical stabilizer is a vertical fixed part of the plane’s empennage. The rudder is a movable piece that’s attached to the vertical stabilizer. The vertical stabilizer isn’t considered a flight control like the rudder because the pilot cannot control it.
How does the rudder work?
If you think about how flaps change the trailing edge of the wings, the rudder works the same way as it changes the trailing edge of the vertical stabilizer. As the pilot pushes the rudder pedals in the front of the plane, cables are connected to the rudder through the fuselage, which moves it left and right. When it is deflected, the angle of attack of the vertical stabilizer changes. As air flows over it, a force like lift results, and the tail is pulled in the opposite direction of the deflection.
To make a simple illustration, think of the vertical stabilizer and rudder together as a wing. But instead of an upward force of lift on a wing, it’s a horizontal force pushing the tail of the plane causing the nose of the plane to move left and right.
Why is the rudder so important?
The main job of the rudder is to counteract adverse yaw and keep the aircraft coordinated. Simply put, if the pilot doesn’t give correct and timely inputs to the rudder, the airplane won’t be pointed in the direction it’s supposed to. This can lead to some potentially dangerous situations, especially if you’re low in the traffic pattern. To better understand rudder use, let’s look at some situations from take-off to landing where you’ll want to have your feet “dancing” on the rudder pedals.
TAXIING
The rudder is vitally important before you even leave the ground. One of the first things a pilot learns is how to steer an aircraft on the ground while taxiing. The pilot controls the throttle to create thrust. As the propeller spins, it creates a slipstream that strikes the rudder. The pilot uses the rudder pedals to control the direction the plane taxis. In calm wind conditions, you don’t even have to touch the yoke to taxi. This is a big learning curve for new pilots that have been using a steering wheel to drive!
TAKEOFF
We’ve been cleared for takeoff, and now you’re lined up on the centerline of the runway. As you increase the power to full throttle, you use the rudder to maintain longitudinal direction and stay on the centerline. Correct rudder use here is evident, because if you don’t apply right rudder you’ll see how quickly your plane wants to travel left and off the runway.
Now we’ve rotated and in the air. Take off and climb out are when you’ll hear your CFI famously say, “More right rudder!” Why is this? Every airplane with a propeller creates a left-turning tendency called P-factor. When the plane is in a climb at high power, the center of lift of the propeller is shifted to the right. This causes the nose of the plane to yaw to the left. To counteract this, the pilot presses on the right rudder pedal to control the yaw of the nose back to the right until the longitudinal direction is straight again.
There are other reasons the nose wants to yaw to the left at high power settings. These are called left turning tendencies and include P-factor, spiraling slipstream, torque, and gyroscopic precession. If you’d like to dive deeper into all of these, check out Chapter 5 (Aerodynamics) in the PHAK (Pilot’s Handbook of Aeronautical Knowledge).
COORDINATED TURNS
Another big job of the rudder is to maintain coordination in a turn. When an airplane starts a turn, there is more lift, and therefore, more drag created in the raised wing. Because of the increased drag, the nose of the plane wants to yaw in the direction of the lifted wing. This is called adverse yaw. A pilot needs slight rudder to offset the adverse yaw. Will the plane turn without rudder? Yes, it can, but the nose will be yawing around and the turn won’t be coordinated.
Uncoordinated turns cause skidding or slipping turns and can lead to stall-spin situations. This is especially dangerous at low altitudes, such as in the traffic pattern, where there’s not enough altitude to recover from a spin.
APPROACH AND LANDING
Now we’re approaching the airport and ready to land. On final, as power is low or even idle, the P-factor is reversed, and the nose wants to yaw slightly to the left. However, it’s not nearly as pronounced as on takeoff. Just something to be aware of! A pilot might have to use more aileron inputs, especially if it’s bumpy and the aircraft is getting moved around. When aileron input is added to counteract this, just remember that adverse yaw is in play, so some slight rudder will be needed.
As you approach to land, your eyes look down the centerline to the end of the runway. You’ll notice that the nose may not be lined up on centerline. The pilot will need to input correct rudder to maintain correct longitudinal direction. This is especially vital during crosswind landings. If the plane lands with the wheels at an angle (called side-loading), at best it will wear down the sidewalls of the tires. At worst, it could completely damage the wheels/gear and cause an accident.
How do I know that rudder input is needed?
Now you know what the rudder is, how it works, and the main situations you want to use it properly. One indication of being uncoordinated is a feeling of sideways force in your seat. In some aircraft, this feeling is more pronounced. However, the manufacturers of most light trainers have made excellent designs where it’s not as easily noticed. Another way that uncoordinated flight is indicated is with the inclinometer at the bottom of the turn coordinator instrument. (If your plane has a PFD this looks like an arrow over a line that moves at the top of the display.)
The “ball” looks like a miniature level that you’d use in construction. If the ball slides to the left, you need to input more left rudder. If it slides to the right, you need more right rudder. The goal is to have the ball always centered. This is what your CFI means when they say, “Step on the ball!”
As you begin to fly more advanced aircraft, such as a multi-engine or tailwheel aircraft, proper rudder use becomes even more important. Make it a goal to give the rudder the respect it deserves, and don’t fly sloppy. It will set you apart as an aviator, not just a pilot, and keep you flying safely.
By Leslie Caubble, CFI/IGI
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