Roll control by spoilers

Spoilers are small surfaces which are designed to spoil the flow over a wing and thus reduce its lift. They normally take the form of small hinged plates which, when deployed, project up into the flow on the top surface of the wing.

ailerons

Fig. 10.10 Spoilers, ailerons and flaps on a Boeing 747

Spoilers were originally used as a means of producing drag to slow an air­craft down. They were also fitted to gliders, in order to control descent rate on approach, shorten the landing run and to ensure that once landed, the aircraft stayed down. Nowadays, spoilers are fitted to most large aircraft, being used differentially (deployed on one wing and retracted on the other) to provide roll control, or collectively (deployed simultaneously on both wings) to provide a means of increasing drag and reducing lift. Figure 10.10 shows the spoiler and aileron locations on a Boeing 747 ‘Jumbo’.

Since spoilers are often used in combination with ailerons in a complicated way, and may only operate under certain flight conditions, some degree of automation is necessary in the spoiler control mechanisms. A good description of the use of spoilers on large aircraft is contained in Davies (1971).