Flight controls
Primary flight controls

Are controls which movement causes a rotation about one of the three axes of the aircraft, causing a change in the aircraft’s flightpath or attitude. The elevator, rudder and ailerons are considered to be the primary flight controls. The primary flight controls in a manually controlled system are reversible. This means that a force applied to the controls is a force which moves the control surface, and also a force which moves the control surface will move the pilot’s controls. This means that the air pressure on the control surface can be felt in the pilot’s controls. When the flight controls are fully power operated this is not the case and is called irreversible. This means that if there is a force moving the control surface this will not move the control columns, and there will be no natural feel on the controls.

Because of this there will need to be an artificial feel unit installed in a fully powered or irreversible control system. This artificial feel unit should apply force to the cockpit controls in proportion to the control deflection and in proportion to the aircraft’s speed.

This artificial feel system will also work with a trim system, but this works different than a normal trim surface does. In the figure in the annex you can see how the trim of the artificial feel unit works. A movement of the trim wheel will result in a movement of the electric trim actuator, and so the control surface, but not in the movement of the control column (this is for elevator control). It is different for aileron and rudder trim.

Elevator trim: zero force position of the control column does not change (control column/horn/stick does not move)
Aileron trim: zero force position changes (control wheel turns in the direction of the trim)
Rudder trim: zero force position changes (pedals move in the direction of the trim)