RE Museum - Power-assisted controls

Power-assisted aircraft controls
On modern aircraft, the controls are power assisted, operating by hydraulic pressure. This gives the force needed to move control surfaces against the airflow at high speed. Most modern planes fly on autopilot - an automatic control system often nicknamed `George' - for much of the time.

This is computer-controlled from data fed in by measuring instruments that sense changes in conditions, such as wind speed, deviation and pitch. Once the autopilot has been set for a particular course, height and speed, it will manipulate the throttle and control surfaces as necessary.

Taking off and landing

Takeoff and landing are the two most critical flight manoeuvres. Because the plane must be travelling more slowly, the wings develop less lift.
To increase the lift at low speeds, the wings have other control surfaces - flaps at the rear and slats at the front. The flaps extend out and down on tracks, and as they extend they increase the wing area and exaggerate its camber, increasing the lift.

The slats, fitted on the leading edge of the wings, are movable curved surfaces. When they open, they improve the airflow around the wing, again increasing the lift.

After the plane has touched down, the problem is not to increase lift, but to kill it. This is done by means of spoilers (or speed brakes) - hinged surfaces usually located in front of the flaps. They are opened immediately on landing and hinge upwards at right-angles to the wing. This increases drag, breaking up the airflow over the top of the wings so that the wing loses all its lift. Initial braking is effected by applying reverse thrust - a jet engine has a mechanism that can deflect the exhaust gases forward.

Once the plane is travelling slowly enough, the pilot applies the wheel brakes.

Read More: How Jets Work