The ability of an airplane to return to its original orientation after a gust of wind or an unexpected bit of turbulence, without the pilot intervening, is called stability. Another way to think about the stability is the ability of the plane to fly itself! The small airplanes used at local airports are very stable; they are good for both beginning pilots and the more experienced pilots who use them for transportation. They are very easy to fly and very forgiving of pilot mistakes. Commercial aircraft are moderately stable; pilots pay attention and fly them, but the planes are built so that they turn smoothly and don't upset the passengers. Some military aircraft, especially fighters, aren't very stable at all. This makes the aircraft much more complicated to fly, but gives the pilot maximum maneuverability. This could be very important in an aerial dogfight!

The pilot can change the motion of an airplane by redirecting, increasing, decreasing, or eliminating the various forces on the aircraft. The ability to do this is called control. Using control surfaces such as the rudder, ailerons, elevators, or spoilers, the pilot changes the way the forces of flight act on the airplane and causes it to change its direction. The pilot can change the lift amount by changing the angle of attack, the angle the plane flies with respect to the air flow. He or she can change the lift direction by turning the plane. The drag can be changed by using the control surfaces to change the shape of the wings. And, lastly, the pilot can change the thrust by throttling the engines up or down. In an emergency, some planes can also dump fuel to lighten the weight. Thus, all four forces of flight can be changed by controls.

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Last modified: Sun Aug 2 11:53:00 PDT 1998

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