Stabilizer (aeronautics)
A horizontal stabilizer is used to maintain the aircraft in longitudinal balance, or trim:[3] it exerts a vertical force at a distance so the summation of pitch moments about the center of gravity is zero.
[6] This maintains a constant aircraft attitude, with unchanging pitch angle relative to the airstream, without active input from the pilot.
The upwash and downwash associated with the generation of lift is the source of aerodynamic interaction between the wing and stabilizer, which translates into a change in the effective angle of attack for each surface.
The influence of the wing on a tail is much more significant than the opposite effect and can be modeled using the Prandtl lifting-line theory; however, an accurate estimation of the interaction between multiple surfaces requires computer simulations or wind tunnel tests.
Stabilators are also found in many supersonic aircraft, where a separate elevator control would cause unacceptable drag.
[8] Most airliners and transport aircraft feature a large, slow-moving trimmable tail plane which is combined with independently-moving elevators.
In the Boeing 737, the adjustable stabilizer trim system is powered by an electrically operated jackscrew.
Some earlier three-surface aircraft, such as the Curtiss AEA June Bug or the Voisin 1907 biplane, were of conventional layout with an additional front pitch control surface which was called "elevator" or sometimes "stabilisateur".
Instead wing sweep and dihedral can provide a similar degree of directional stability, while directional control is often effected by adding drag on the side of the aircraft the aircraft is to be turned towards, either in the form of spoilers or split ailerons.
On some aircraft, horizontal and vertical stabilizers are combined in a pair of surfaces named V-tail.
In this arrangement, two stabilizers (fins and rudders) are mounted at 90–120° to each other,[note 1] giving a larger horizontal projected area than vertical one as in the majority of conventional tails.
