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 and prevent dangerous overspeed; and when the aircraft banks, the stabilizer produces lift which counters the banking moment and keeps the aircraft upright in the absence of control input. If the vertical stabilizer was mounted on the underside, it would produce a positive feedback whenever the aircraft dives or banks, 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.