stabilizer

The vertical stabilizers, vertical stabilisers, or fins, of aircraft, missiles or bombs are typically found on the aft end of the fuselage or body, and are intended to reduce aerodynamic side slip and provide direction stability. It is analogous to a skeg on boats and ships.
On aircraft, vertical stabilizers generally point upwards. These are also known as the vertical tail, and are part of an aircraft's empennage. This upright mounting position has two major benefits: The drag of the stabilizer increases at speed, which creates a nose-up moment that helps to slow down the aircraft that prevent dangerous overspeed, and when the aircraft banks, the stabilizer produces lift which counters the banking moment and keeps the aircraft upright at the absence of control input. If the vertical stabilizer was mounted on the underside, it would produce a positive feedback whenever the aircraft dove or banked, which is inherently unstable. The trailing end of the stabilizer is typically movable, and called the rudder; this allows the aircraft pilot to control yaw.
Often navigational radio or airband transceiver antennas are placed on or inside the vertical tail. In all known trijets (jet aircraft with 3 engines), the vertical stabilizer houses the central engine or engine inlet duct.
Vertical stabilizers, or fins, have also been used in automobiles, specifically in top level motor sports, with the concept making a resurgence in both Formula 1 and Le Mans Prototype racing.
A few aircraft models have a ventral fin under the rear end. Normally this is small, or can fold sideways, to allow landing. Both the North American X-15 supersonic/hypersonic experimental aircraft, and the late World War II German twin-engined Dornier Do 335 heavy fighter used differing forms of the cruciform tail stabilizing surface format.

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