Wing-Mounted Control-Surface Layout

Chapter 3 introduces a host of wing-mounted control surfaces (e. g., aileron, flap, slat, spoilers, and trim tabs), none of which are sized in this book; however, geometry from current designs is extracted and their placement should be earmarked. Control surface sizing is accomplished after the wing is sized and is addressed in subsequent design phases.

Flaps and slats are wing components that are selected for field-performance demands to generate high lift. In general, the more demanding aircraft-performance requirements, the more sophisticated are the high-lift devices, which are progres­sively more complex and therefore more expensive (see Section 3.12). Associated incremental lift gains by each type are shown in Figure 3.21. In general, a single – or double-slotted Fowler action flap suffices for the majority of civil transport aircraft. The simpler types are less costly to manufacture and are used in low-speed, low-cost smaller aircraft, usually compensated by the relatively larger wing area.

The aileron span is about a third of the wing span at the extremities. Ailerons and flaps are hinged aft of the rear spar for up and down movements; provision for them should be made during the conceptual design phase. On some designs, flap tracks are used to support the flaps traveling outward to increase lift. A flaperon serves as both a flap and an aileron.

Flaps are positioned behind the wing rear spar (about 60 to 66% of the chord) and typically run straight or piecewise. Flaps take up about two thirds of the inner wing span. It is apparent that designers must have a good knowledge of the inter­nal structural layout to configure an aircraft. Chapter 15 provides information on aircraft structure pertaining to the aircraft-configuration study.

Not all aircraft have wing spoilers; however, aircraft with speed over Mach 0.6 generally have spoilers. These are installed close to the aircraft CG line to mini­mize pitch change. Spoilers also act as air brakes. The differential use of spoilers is for lateral control and they are referred to as spoilerons. This book does not size spoilerons or air brakes but schematically earmarks their position on the wing.

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