Vertical stabilizer
Moving it allows the pilot to control yaw about the vertical axis, i.e., change the horizontal direction in which the nose is pointing.
[10] For taxiing and during the beginning of the take-off, aircraft are steered by a combination of rudder input as well as turning the nosewheel or tailwheel.
[citation needed] Changing the setting of a trim tab adjusts the neutral or resting position of a control surface (such as an elevator or rudder).
As the desired position of a control surface changes (corresponding mainly to different speeds), an adjustable trim tab will allow the operator to reduce the manual force required to maintain that position—to zero, if used correctly.
[citation needed] The vertical tail plays a determining role in yaw stability, providing most of the required restoring moment about the center of gravity when the aircraft slips.
[6] The airflow over the vertical tail is often influenced by the fuselage, wings and engines of the aircraft, both in magnitude and direction.
[6] Dihedral in the main wing and horizontal tail can also have a small effect on the static yaw stability.
[6] Propellers, especially when they are advancing so that their axis makes an angle to the freestream velocity, can affect the static stability of an airplane in yaw.
[1] When the aircraft slips to the right, the relative wind and side force on the vertical tail translate into an anti-clockwise moment in roll.
[6] In supersonic flight, the vertical tail becomes progressively less effective with increasing Mach number until the loss of stability may no longer be acceptable.
Extra area may be added by installing ventral fins (such as on higher-speed, later versions of the Vought F-8 Crusader), or folding-down wingtips (such as on the North American XB-70 Valkyrie).
An extreme case occurs with a departure from controlled flight, known as an upset, which in the context of fin and rudder is excessive sideslip.
[17] Clear air turbulence caused the failure of the complete fin and rudder assembly on a Boeing B-52 Stratofortress after which the pilots made a successful landing.
[19] A Lightning lost its fin due to interaction between aircraft in close proximity at low level when flying in formation at M 0.97, an aerobatic display routine.
The single fin on the Eurofighter Typhoon experiences buffet loads caused by burst vortices which originate from the canard and wing leading edges at high angles of attack.
[20] The McDonnell Douglas F/A-18 Hornet twin fins are subject to buffeting from the breakdown or bursting of the leading-edge extension (LEX) vortex in front of the tail.
[21] The addition of a LEX fence significantly reduces the buffeting and increases fin fatigue life.
Conventional rudders would have been inadequate for the SR-71 because excessive deflections would have been required for the engine-out case causing unacceptable trim drag.
The twin rudders may be used in the gear-down configuration for additional longitudinal control with toe-in or flare-out (McDonnell Douglas F/A-18 Hornet[28]).
[29] A twin tail may be either H-tail, twin fin/rudder construction attached to a single fuselage, such as North American B-25 Mitchell medium bomber or Avro Lancaster, or twin-boom where the rear airframe consists of two separate boom structures each with one single fin and rudder joined by a horizontal stabiliser, such as North American Rockwell OV-10 Bronco or Armstrong Whitworth AW.660 Argosy transport.
The Lockheed Constellation used three fins to give the airplane the required vertical stabilizer area while at the same time keeping the overall height low enough so that it could fit into hangars for maintenance.
The top part of the vertical fin on the North American A-5 Vigilante folds to the side due to the hangar deck height restriction.
[30] Some Formula 1 teams utilized a vertical stabilizer as a way to disrupt the airflow to the rear wing reducing drag, the most radical system being the "F-duct" found in the 2010 McLaren MP4-25 and Ferrari F10.
On demand by the driver, this system diverted air from a duct in the front of the car through a tunnel in the vertical fin onto the rear wing to stall it and reduce drag on the straights on which downforce was not needed.
