by W D Adkins

Created on: April 27, 2008   Last Updated: May 05, 2008

If you've ever watched pilots performing acrobatic stunts, you know they do some amazing and complicated maneuvers. Yet, no matter how complex they are, all the movements of the plane can be described in terms of just four types of motion. The first, when the aircraft is flying straight and level, is forward motion, or airspeed. But airplanes don't just travel in straight and level paths; they move in three dimensions. The remaining three types of motion are movement around the aircraft's three axes of rotation: the longitudinal axis, the lateral axis, and the vertical axis. Anytime an aircraft rotates around one of these axes, it changes the way the air flows over the aircraft's surface, causing it to turn, climb, roll, and so forth.

You can think of the longitudinal axis as an imaginary line running from the aircraft nose to its tail, passing through the center of gravity. When one wing goes up and the other goes down, the airplane is rotating around the longitudinal axis, and this kind of motion is called roll.

The lateral axis can be visualized as a line from wingtip to wingtip, again passing through the center of gravity and perpendicular to the longitudinal axis. If the aircraft starts to climb, the nose goes up and the tail drops, so the aircraft rotates around the lateral axis. Pilots call this kind of rotation pitch.

The vertical axis is much the same, except it is straight up and down, passing through the center of gravity at right angles to the other two axes. When the aircraft's nose swings to the left or right, it is rotating around the vertical axis, which is called yaw.

The important and interesting thing about rotating an aircraft around its axes of rotation is that this is how pilots control the aircraft. To understand how this works, first you need to know what is meant by aircraft stability. Aircraft are carefully designed to be as stable as possible. If the equilibrium (balance of forces) on the aircraft is disturbed, it always tends to return to its original equilibrium. Anytime the pilot wants to turn or perform any other maneuver, a force of some sort must be applied.

There are three basic types of control surfaces that pilots use to do this: ailerons, rudder, and elevators. Each is moved to change the way the air hits the aircraft as it flies, producing a particular force on some part(s) of the aircraft.

The ailerons are located on the trailing edge of the wings. To turn the aircraft to the left, the pilot will raise the left aileron and lower

• 1
• 2
• Next Page >>