What It Looks Like

Next time you go to the airport, look closely at the leading edges of the wings on various airplanes, especially high-performance models. You may find long, narrow, triangular-shaped wedges attached to some of the leading edges. These are called stall strips.

The short explanation of the purpose of a stall strip is to "force" an aerodynamic stall. But wait a minute - airplanes aren't supposed to stall, or, to state it more precisely, pilots aren't supposed to allow an airplane to stall except in a controlled training situation or when performing aerobatics in a properly certificated and equipped airplane. That begs the question of why an airplane manufacturer would attach devices to the wing leading edge that have the effect of forcing the wing to stall.

Here's why: For safety's sake, the most desirable stall pattern is one that begins in the root region of the wing, close to the fuselage. If the wing root stalls before the outboard portion of the wing at stall-producing high angles of attack, the ailerons remain effective, and the pilot can maintain roll control. Also, turbulent air resulting from a stall in the wing root area buffets the empennage and aft portion of the fuselage, giving the pilot an unmistakable warning that the wing is indeed stalling and the nose needs to be lowered immediately. Finally, the loss of downwash behind the wing root can provide a stable nose-down pitching moment for positive recovery from the stall.

If the aerodynamic stall begins at the wing tips and progresses inboard toward the wing root, the pilot likely will experience sudden wing drop with little or no warning buffet, no nose-down pitching moment, and no aileron effectiveness.

So, if the wing is going to stall, it ought to do so in the root area first. Stall strips help to make sure that is the case. The strips cause an aerodynamic stall-separation of airflow over the wing-to occur at a lower angle of attack than if the strips were not in place.

The length and location of stall strips is determined through extensive flight testing by the manufacturer. Once the optimum configuration is set, the strips are permanently attached to the leading edge and are not to be removed.