What Are Those Sharp Things On The Wing?
If you’ve ever preflighted an airplane, you likely noticed small wedge-shaped strips on the front of the wing. These are called stall strips, and they play a crucial role in a wing’s design.
Stall strips contribute to a more controlled stall across the wing and increase wing buffeting before a full stall occurs. So, how do they work? It all starts with the concept of 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, while 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. However, when the wing is at a high AOA, the stagnation point shifts below the leading edge.
How The Stall Strip Helps
Stall strips come into play when your wing is at a high AOA. Since the stagnation point is on the underside of the wing, air flows upward and around the leading edge, eventually reaching over the top of the wing. Without a stall strip, airflow can remain attached to the wing during this process.
But because the stall strip is sharp, airflow has a harder time adhering, and it starts to detach from the wing before the wing reaches the critical AOA and stalls. This results in an “early” stall directly behind the strip, before the entire wing stalls.
Stall strips are typically quite small and are placed near the root of the wing (next to the fuselage). The idea behind their location is simple: you want the wing to stall in a desirable area, which is usually the root. When the root stalls first, you still have aileron roll control in the early stages of the stall (wing washout also contributes to this, and we’ll cover that here).
Buffet Warning
There’s an additional benefit to stall strips: wing buffeting. Because the small section of wing behind the strip stalls earlier than the rest of the wing, you’ll experience a buffet from airflow separation a few knots before the actual stall. It’s a valuable addition to your stall warning indicator.
Do Your Wings Have Them?
The next time you’re at the airport and look at the leading edges of the airplanes on the ramp, you’ll find that almost every type of aircraft has stall strips, from training airplanes to corporate jets. And once you see them, you’ll understand exactly what they’re for.
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