In addition to primary structural and control components, aircraft wings often incorporate aerodynamic devices designed to improve performance, handling, and efficiency. Winglets, vortex generators, stall fences, and gap seals are all common wing features. The following sections provide an overview of these common wing features and their functions.
Winglets
A winglet is a vertical extension at the tip of a wing that resembles a small vertical stabilizer. It is an aerodynamic device designed to reduce the drag created by wing tip vortices in flight. Usually made from aluminum or composite materials, winglets can be designed to optimize performance at a desired speed. [Figure 1]
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| Figure 1. A winglet reduces aerodynamic drag caused by air spilling off of the wing tip |
Vortex Generators
Vortex generators are small airfoil sections usually attached to the upper surface of a wing. [Figure 2]
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| Figure 2. Vortex generators |
They are designed to energize the boundary layer and delay airflow separation over the wing and control surfaces. Usually made of aluminum and installed in one or more spanwise rows, the vortices created by these devices mix higher-energy air into the boundary layer, helping it remain attached to the wing surface at higher angles of attack. They can also be found on the fuselage and empennage. Figure 3 shows the unique vortex generators installed on a Symphony SA-160 wing.
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| Figure 3. The Symphony SA-160 has two unique vortex generators on its wing to ensure aileron effectiveness through the stall |
Stall Fences
A stall fence is a chordwise barrier installed on the upper surface of a wing to restrict the spanwise flow of air. During low-speed flight, this helps maintain chordwise airflow and reduces the tendency for airflow to migrate spanwise, thereby delaying tip stall and improving stall characteristics. Usually made of aluminum, the fence is a fixed structure most common on swept wings, which naturally promote spanwise airflow across the wing. [Figure 4]
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| Figure 4. A stall fence aids in maintaining chordwise airflow over the wing |
Gap Seals
Often, a gap can exist between the stationary trailing edge of a wing or stabilizer and the movable control surface(s). At high angles of attack, high-pressure air from the lower wing surface can leak through this gap. The result can be turbulent airflow, which increases drag.
There is also a tendency for lower-surface airflow to enter the gap and disrupt the upper wing surface airflow, which in turn reduces lift and control surface responsiveness. Gap seals are commonly used to maintain smooth airflow across these gaps. Gap seals can be made of a wide variety of materials ranging from aluminum and impregnated fabric to foam and plastic. Figure 5 shows some gap seals installed on various aircraft.
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| Figure 5. Gap seals promote the smooth flow of air over gaps between fixed and movable surface |