High-lift device
In
Purpose
The size and lifting capacity of a fixed wing is chosen as a compromise between differing requirements. For example, a larger wing will provide more lift and reduce the distance and speeds required for takeoff and landing, but will increase drag, which reduces performance during the cruising portion of flight. Modern passenger jet wing designs are optimized for speed and efficiency during the cruise portion of flight, since this is where the aircraft spends the vast majority of its flight time. High-lift devices compensate for this design trade-off by adding lift at takeoff and landing, reducing the distance and speed required to safely land the aircraft, and allowing the use of a more efficient wing in flight. The high-lift devices on the Boeing 747-400, for example, increase the wing area by 21% and increase the lift generated by 90%.[1]
Types of device
Flaps
The most common high-lift device is the flap, a movable portion of the wing that can be lowered to produce extra lift. When a flap is lowered this re-shapes the wing section to give it more camber. Flaps are usually located on the trailing edge of a wing, while leading edge flaps are used occasionally. There are many kinds of trailing-edge flap.
Simple hinged flaps came into common use in the 1930s, along with the arrival of the modern fast monoplane which had higher landing and takeoff speeds than the old biplanes.
In the split flap, the lower surface hinges downwards while the upper surface remains either fixed to the wing or moves independently.
Travelling flaps also extend backwards, to increase the
Slotted flaps comprise several separate small airfoils which separate apart, hinge and even slide past each other when deployed. Such complex flap arrangements are found on many modern aircraft.[2] Large modern airliners make use of triple-slotted flaps to produce the massive lift required during takeoff.
Slats and slots
Another common high-lift device is the slat, a small aerofoil shaped device attached just in front of the wing leading edge. The slat re-directs the airflow at the front of the wing, allowing it to flow more smoothly over the upper surface when at a high angle of attack. This allows the wing to be operated effectively at the higher angles required to produce more lift. A slot is the gap between the slat and the wing.[3] The slat may be fixed in position, with a slot permanently in place behind it, or it may be retractable so that the slot is closed when not required. If it is fixed, then it may appear as a normal part of the leading edge of a wing, with the slot buried in the wing surface immediately behind it.
A slat or slot may be either full-span, or may be placed on only part of the wing (usually outboard), depending on how the lift characteristics need to be modified for good low speed control. Slots and slats are sometimes used just for the section in front of the ailerons, ensuring that when the rest of the wing stalls, the ailerons remain usable.
The first slats were developed by
Modern systems, like modern flaps, can be more complex and are typically deployed hydraulically or with servos.[4][5][6]
Boundary layer control and blown flaps
Powered high-lift systems generally use airflow from the engine to shape the flow of air over the wing, replacing or modifying the action of the flaps.
Another approach is to use the airflow from the engines directly, by placing a flap so that it deploys into the path of the exhaust. Such flaps require greater strength due to the power of modern engines and also greater heat resistance to the hot exhaust, but the effect on lift can be significant. Examples include the
Leading edge root extensions
More common on modern
Co-Flow Jet
A Co-Flow Jet (CFJ) wing has an upper surface with an injection slot after the leading edge and a suction slot before the trailing edge, to augment lift, increase the stall margin and reduce drag. CFJ is promoted by the mechanical and aerospace engineering department of the University of Miami. For a hybrid-electric
See also
- Boundary layer control
- Circulation control wing
- Chine (aircraft)
References
Notes
- ^ Colin Cutler (November 19, 2014). "16 Little Known Facts About The Boeing 747". www.boldmethod.com. Retrieved March 22, 2016.
- ^ Taylor 1990, p. 337.
- ^ Kermode, A.C. Mechanics of flight, 8th Edn., Pitman, 1972
- ^ Taylor 1990, p. 346
- ^ Taylor 1990, p. 399.
- ISBN 9780521021289.)
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: CS1 maint: location (link - ^ Graham Warwick (Jan 21, 2019). "The Week In Technology, Jan. 21-26, 2019". Aviation Week & Space Technology.
Bibliography
- Taylor, John W.R. The Lore of Flight, London: Universal Books Ltd., 1990. ISBN 0-9509620-1-5.