Editing Flight control surfaces (section)

==Control trimming surfaces==
{{main|Trim tab}}

Trimming controls allow a pilot to balance the lift and drag being produced by the wings and control surfaces over a wide range of load and airspeed.  This reduces the effort required to adjust or maintain a desired flight [[Aircraft attitude|attitude]].

===Elevator trim===

Elevator trim balances the control force necessary to maintain the correct aerodynamic force on the tail to balance the aircraft. Whilst carrying out certain flight exercises, a lot of trim could be required to maintain the desired angle of attack. This mainly applies to [[slow flight]], where a nose-up attitude is required, in turn requiring a lot of trim causing the tailplane to exert a strong downforce.  Elevator trim is correlated with the speed of the airflow over the tail, thus airspeed changes to the aircraft require re-trimming. An important design parameter for aircraft is the stability of the aircraft when trimmed for level flight.  Any disturbances such as gusts or turbulence will be damped over a short period of time and the aircraft will return to its level flight trimmed airspeed.

====Trimming tail plane====
Except for very light aircraft, trim tabs on the elevators are unable to provide the force and range of motion desired. To provide the appropriate trim force the entire horizontal tail plane is made adjustable in pitch. This allows the pilot to select exactly the right amount of positive or negative lift from the tail plane while reducing drag from the elevators.

====Control horn====
[[File:Mass Balancing ME Bf110.jpg|thumb|Mass balance protruding from an aileron used to suppress flutter]]
A control horn is a section of control surface which projects ahead of the pivot point.  It generates a force which tends to increase the surface's deflection thus reducing the control pressure experienced by the pilot. Control horns may also incorporate a [[counterweight]] which helps to balance the control and prevent it from [[Aeroelasticity#Flutter|fluttering]] in the airstream. Some designs feature separate anti-flutter weights.

(In radio controlled model aircraft, the term "control horn" has a different meaning)<ref>{{Cite web |url=http://www.pc-control.co.uk/servo_control.htm |title="Servo Control" |access-date=2012-10-23 |archive-date=2017-09-16 |archive-url=https://web.archive.org/web/20170916201805/http://www.pc-control.co.uk/servo_control.htm |url-status=dead }}</ref><ref>[http://www.modelaircraft.org/mag/FAQ/answers/faq-q28.htm Model Aircraft: control horn FAQ] {{Webarchive|url=https://web.archive.org/web/20130513083300/http://www.modelaircraft.org/mag/FAQ/answers/faq-q28.htm |date=2013-05-13 }}</ref>

====Spring trim====
In the simplest arrangement, trimming is done by a mechanical [[Spring (device)|spring]] (or [[Bungee cord|bungee]]) which adds appropriate force to augment the pilot's control input. The spring is usually connected to an elevator trim lever to allow the pilot to set the spring force applied.

===Rudder and aileron trim===

Most fixed-wing aircraft have a trimming control surface on the [[elevator (aircraft)|elevator]], but larger aircraft also have a trim control for the rudder, and another for the ailerons. The rudder trim is to counter any asymmetric thrust from the engines. Aileron trim is to counter the effects of the [[centre of gravity]] being displaced from the aircraft centerline. This can be caused by fuel or an item of payload being loaded more on one side of the aircraft compared to the other, such as when one fuel tank has more fuel than the other.