What Are Those Sharp Things On The Wing?
If you've ever preflighted an airplane, you probably noticed small wedge-shaped strips on the front of the wing. They're called stall strips, and they're a pretty important part of a wing's design.
Stall strips create a more controlled stall across the wing, as well as increased wing buffeting before a full stall occurs. So how do they work? It starts with something called the stagnation point.
The Stagnation Point
When air approaches the leading edge of your wing, it divides. Some air flows over the top of the wing, and some flows under the bottom. The spot where the airflow splits is called the "stagnation point."
When your wing is at a low angle of attack (AOA), the stagnation point is on the leading edge, and when your wing is at a high angle of attack, the stagnation point moves below the leading edge.
How The Stall Strip Helps
Stall strips begin working when your wing is at a high angle of attack. Because the stagnation point is on the underside of the wing, air flows up and around the leading edge, making its way over the top of the wing. With no stall strip, airflow can stay attached to the wing as this happens.
But since the stall strip is sharp, airflow can't stay attached as easily, and it starts to separate from the wing before your wing reaches the critical AOA and stalls. This causes an "early" stall directly behind the strip, and prior to the entire wing stalling.
Stall strips are typically fairly small, and placed near the root of the wing (next to the fuselage). The idea behind their location is simple: you want your wing to begin stalling in a desirable location, which is typically the root. When the root of the wing stalls first, you still have aileron roll control in the stall's early stages (wing washout also contributes to this, and we cover that here).
Buffet Warning
There's an added benefit to stall strips: wing buffeting. Because the small section of wing behind the strip stalls before the rest of the wing, you'll feel a buffet from airflow separation several knots before you actually stall. It's a good addition to your stall warning indicator.
Do Your Wings Have Them?
The next time you head out to the airport, check out the leading edges of the airplanes on the ramp. You'll find almost every kind of aircraft with stall strips, from training airplanes to corporate jets. And when you see them, you'll know exactly what they're used for too.
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