Auxiliary aerodynamic devices are used to improve lift, reduce drag, enhance controllability, or assist in deceleration during various phases of flight.
These devices can be divided into two primary categories: lift-augmenting devices and lift-decreasing devices. Lift-augmenting devices include trailing-edge flaps, leading-edge slats, and slots. Lift-decreasing devices include spoilers and speed brakes.
Lift-Augmenting Devices
Flaps are located on the trailing edge of the wing and can be extended to increase wing camber and, in some designs, wing area. This increases lift at lower airspeeds, improving takeoff and landing performance. These airfoils are retractable and fair into the wing contour. Others are simply a portion of the lower skin that extends into the airstream, thereby increasing drag and slowing the aircraft.
Leading-edge flaps, also referred to as slats, are movable airfoils that extend from and retract into the leading edge of the wing. When extended, they create a slot between the slat and the wing leading edge. Some aircraft have permanent slots built into the wing's leading edge. [Figure 1]
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| Figure 1. Types of wing flaps |
At low airspeeds, the slot directs high-energy air over the upper wing surface, delaying airflow separation and increasing lift. This improves low-speed handling characteristics and allows the aircraft to be controlled safely at speeds below the normal landing speed. At cruising speeds, both trailing-edge flaps and leading-edge slats are retracted into the wing to minimize drag. [Figure 2]
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| Figure 2. Wing slots |
Lift-Decreasing Devices
Lift-decreasing devices include spoilers and speed brakes. While spoilers primarily reduce lift and increase drag, speed brakes are designed primarily to increase drag and reduce aircraft speed. In some installations, there are two types of spoilers. The ground spoiler is extended only after the aircraft is on the ground, thereby assisting in the braking action. The flight spoiler assists in lateral control by being extended whenever the aileron on that wing is rotated up. When actuated as speed brakes, the spoiler panels on both wings raise up. In-flight spoilers may also be located along the sides, underneath the fuselage, or at the tail. [Figure 3]
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| Figure 3. Speed brake |
In some aircraft designs, the wing panel on the up-aileron side rises more than the wing panel on the down-aileron side. This provides speed-brake operation and lateral control simultaneously.
Other Aerodynamic Devices
In addition to lift-augmenting and lift-decreasing devices, aircraft may incorporate other aerodynamic features that improve efficiency, handling qualities, and stall characteristics.
Winglets
Winglets are near-vertical extensions attached to the wingtips that reduce the aerodynamic drag associated with wingtip vortices. By reducing induced drag, winglets improve fuel efficiency and increase aircraft range. Figure 4 shows an example of a Learjet 60 equipped with winglets.
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| Figure 4. Winglets on a Bombardier Learjet 60 |
Canard Wings
A canard aircraft is a fixed-wing aircraft configuration in which a small wing or horizontal airfoil is located ahead of the main lifting surfaces rather than behind them as in a conventional aircraft. The canard may be fixed, movable, or equipped with elevators. Examples of canard-configured aircraft include the Rutan VariEze and the Beechcraft Starship. [Figures 5 and 6]
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| Figure 5. Canard wings on a Rutan VariEze |
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| Figure 6. The Beechcraft 2000 Starship has canard wings |
Wing Fences
Wing fences are flat vertical plates attached to the upper surface of a wing. They reduce spanwise airflow and help prevent the entire wing from stalling simultaneously. Wing fences are commonly installed on swept-wing aircraft to limit airflow toward the wingtips at high angles of attack, improving low-speed handling and stall characteristics. [Figure 7]
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| Figure 7. Aircraft stall fence |