Stall strips
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A stall strip is a fixed aerodynamic device employed on fixed-wing aircraft to modify the airfoil used. They are usually factory-installed or, on rarer occasion, an after-market modification. Stall strips are almost always employed in pairs, symmetrically on both wings. In rare installations they are employed as a single strip on one wing to correct aberrant stall behaviour.
A stall strip alters the wing’s stall characteristics and ensures that the wing root stalls before the wing tips. This is usually as a result of initial aircraft flight testing which shows that the existing stall characteristics are unacceptable for certification.
In some cases, such as the American Aviation AA-1 Yankee, stall strips are planned to be used on the wing from the start. In the case of the AA-1 the left and right wings were identical, interchangeable and built on a single wing jig, thus the more traditional use of washout in the wing design was not possible.
Stall strips can be an alternative to washout in aircraft design or they can be used as well as washout to improve stall performance.
Stall strips typically consist of a small piece of material, usually aluminium, triangular in cross section and often 6-12 inches (15-30 cm) in length. It is riveted or bonded on the point of the wing’s leading edge, usually at the wing root. Here it acts to trip the boundary layer air flow at higher angles of attack, causing turbulent flow and air flow separation. This has the effect of causing the wing root to stall before the outer portions of the wing, ensuring a progressive outward stall and aileron control through the stall.
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