The Axes of an Airplane
Airplanes do not move like cars! Cars only move in two dimensions: you can drive forwards or backwards, or you can turn left or right. Airplanes can do all of this, and they also move in a third dimension: they can go up or down!
Stand up where you are. Imagine that there is a pole that goes through your stomach, joining your belly button and your back. How would you move around this pole if someone pushed you? You would roll to your left or to your right, depending on how you were pushed. This pole is an "axis". An axis is an imaginary line that an object can move around. There are three of them, and they all have different names. The one going from your belly button to your back is called the "longitudinal axis". A movement around the longitudinal axis is called rolling.
Now imagine a pole running through your body from your left side to your right side. If someone pushed you, you would flip forward, head over heels, as if you were doing a summersalt. This axis is called the "lateral axis". A movement around the lateral axis is called "pitching".
Finally, imagine a pole that goes down through the top of your head, all the way to your toes. The only way to move around this axis is to spin around, as if you were doing an about turn. This axis is called the "vertical axis" because it goes from top to bottom. You may also hear it called the "normal axis". A movement around the vertical axis is called "yaw".
On an airplane, these axes are the same. The longitudinal axis runs from the nose of the airplane to the tail. The lateral axis runs from the left wing tip to the right wing tip. The normal (or vertical) axis runs from the top of the airplane, to the bottom of the airplane.
The place where all three of the axes cross is called the centre of gravity.
You will remember from previous sections that the movement of the airplane is controlled by three main control surfaces: the rudder, the elevator, and the ailerons. The rudder causes the airplane to yaw around the vertical axis. The elevator causes the airplane to pitch around the lateral axis, and the ailerons cause the airplane to roll around the longitudinal axis.
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