Longitudinal Balance, Stability and Control
A longitudinal stabilizer is used to maintain the aircraft in longitudinal balance, or trim: it exerts a vertical force at a distance so that the summation of pitch moments about the center of gravity is zero. The vertical force exerted by the stabilizer to this effect varies with flight conditions, in particular according to the aircraft lift coefficient and wing flaps deflection which both affect the position of the center of lift, and with the position of the aircraft center of gravity (which changes with aircraft loading). Transonic flight makes special demands on horizontal stabilizers, since the crossing of the sound barrier is associated with a sudden move aft of the center of lift.
An other role of a longitudinal stabilizer is to provide longitudinal static stability. Stability can be defined only when the vehicle is in trim; it refers to the tendency of the aircraft to return to the trimmed condition if it is disturbed. This maintains a constant aircraft attitude, with unchanging pitch angle relative to the airstream, without active input from the pilot. Since obtaining static stability often requires that the aircraft center of gravity be ahead of the center of lift of a conventional wing, a stabilizer positioned aft of the wing is then often required to produce negative lift.
The elevators serve to control the pitch axis; in case of a fully movable tail, the entire assembly acts as a control surface.
Read more about this topic: Stabilizer (aircraft)
Famous quotes containing the words stability and/or control:
“The message you give your children when you discipline with love is I care too much about you to let you misbehave. I care enough about you that Im willing to spend time and effort to help you learn what is appropriate. All children need the security and stability of food, shelter, love, and protection, but unless they also receive effective and appropriate discipline, they wont feel secure.”
—Stephanie Marston (20th century)
“We as a nation need to be reeducated about the necessary and sufficient conditions for making human beings human. We need to be reeducated not as parentsbut as workers, neighbors, and friends; and as members of the organizations, committees, boardsand, especially, the informal networks that control our social institutions and thereby determine the conditions of life for our families and their children.”
—Urie Bronfenbrenner (b. 1917)