The vertical stabilizer on a plane is designed to stabilize the left-right motion of the aircraft. While most aircraft use a single stabilizer, some models, such as the Lockheed C-69 Constellation use multiple, smaller stabilizers.
The vertical stabilizer on a plane tail is the aerodynamic surface that must provide sufficient directional equilibrium, stability, and control. Its sizing is determined by critical conditions as minimum control speed with one engine inoperative (for multi-engine airplanes) and landing in strong crosswinds.
The airborne minimum control speed VMC is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that engine still inoperative and maintain straight flight with an angle of bank of not more than 5° . The airborne minimum control speed may not exceed 1.13 times the reference stall speed. Thus, it affects the takeoff field length, which must be kept as low as possible otherwise payload could be reduced when the aircraft is operating on short runways. The VMC involves large rudder angles dr to keep a small angle of sideslip b. See Figure 1 left. This requires a certain vertical tail area for a given rudder effectiveness t, which must be the ighest possible to keep control authority at 25° or more of rudder deflection