Terms in this set (104)

-Slots operate by allowing the high static pressure air beneath the wing to be accelerated through a nozzle and injected into the boundary layer on the upper surface of the airfoil (Figure 3-6). As the air is accelerated through the nozzle, its potential energy is converted to kinetic energy. Using this extra kinetic energy, the turbulent boundary layer is able to overcome the adverse pressure gradient and adhere to the airfoil at higher AOAs. There are generally two types of slots, fixed slots and automatic slots.
-Fixed slots are gaps located at the leading edge of a wing that allow air to flow from below the wing to the upper surface. High pressure air from the vicinity of the leading edge stagnation point is directed through the slot, which acts as a nozzle converting the static pressure into dynamic pressure. The high kinetic energy air leaving the nozzle increases the energy of the boundary layer and delays separation. This is very efficient and causes only a small increase in drag.
-Slats are moveable leading edge sections used to form automatic slots. When the slat deploys, it opens a slot. Some slats are deployed aerodynamically. At low AOA, the slat is held flush against the leading edge by the high static pressure around the leading edge stagnation point. When the airfoil is at a high AOA, the leading edge stagnation point and associated high pressure area move down away from the leading edge and are replaced by a low (suction) pressure which creates a chordwise force forward and actuates the slat. Other automatic slots are deployed mechanically, hydraulically or electrically.
-A plain flap is a simple hinged portion of the trailing edge that is forced down into the airstream to increase the camber of the airfoil.
-A split flap is a plate deflected from the lower surface of the airfoil. This type of flap creates a lot of drag because of the turbulent air between the wing and deflected surface.
-A slotted flap is similar to the plain flap, but moves away from the wing to open a narrow slot between the flap and wing for boundary layer control. A slotted flap may cause a slight increase in wing area, but the increase in lift is insignificant.
The fowler flap is used extensively on larger airplanes. When extended, it moves down, increasing the camber, and aft, causing a significant increase in wing area as well as opening one or more slots for boundary layer control. Because of the larger area created on airfoils with fowler flaps, a large twisting moment is developed. This requires a structurally stronger wing to withstand the increased twisting load and precludes their use on high speed, thin wings.
-Leading edge flaps are devices that change the wing camber at the leading edge of the airfoil. They may be operated manually with a switch or automatically by computer. Leading edge plain flaps are similar to a trailing edge plain flap. Leading edge slotted flaps are similar to trailing edge slotted flaps, but are sometimes confused with automatic slots. Often the terms are interchangeable since many leading edge devices have some characteristics of both flaps and slats.
-The lift distribution on the rectangular wing (λ = 1.0) is due to low lift coefficients at the tip and high lift coefficients at the root. Since the area of the highest lift coefficient will stall first, the rectangular wing has a strong root stall tendency. This pattern provides adequate stall warning and aileron effectiveness. This planform is limited to low speed, light-weight airplanes where simplicity of construction and favorable stall characteristics are the predominating requirements.
-A highly tapered wing (λ = 0.25) is desirable from the standpoint of structural weight, stiffness, and wingtip vortices. Tapered wings produce most of the lift toward the tip and have a strong tip stall tendency.
-Swept wings are used on high speed aircraft because they reduce drag and allow the airplane to fly at higher Mach numbers. They have a similar lift distribution to a tapered wing, and therefore stall easily and have a strong tip stall tendency. When the wingtip stalls, the stall rapidly progresses over the remainder of the wing.
-The elliptical wing has an even distribution of lift from the root to the tip and produces minimum induced drag. An even lift distribution means that all sections stall at the same angle of attack. There is little advanced warning and aileron effectiveness may be lost near a stall. It is also more difficult to manufacture than other planforms, but is considered the ideal subsonic wing due to its lift to drag ratio.
-The elliptical wing has an even distribution of lift from the root to the tip and produces minimum induced drag. An even lift distribution means that all sections stall at the same angle of attack. There is little advanced warning and aileron effectiveness may be lost near a stall. It is also more difficult to manufacture than other planforms, but is considered the ideal subsonic wing due to its lift to drag ratio.
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