Definition
A high-lift device mounted on the leading edge of a wing that hinges forward and down from the underside to extend the effective curvature and area of the wing's front edge at low airspeeds. Krueger flaps increase the wing's maximum lift coefficient and stall angle of attack, allowing slower approach and takeoff speeds. They are typically found on larger transport-category aircraft and are deployed in conjunction with trailing edge flaps during takeoff and landing.
Plain English
A panel on the front edge of the wing that swings forward and down to make the wing curvier and bigger when the airplane is flying slowly. This lets the airplane keep flying safely at slower speeds during takeoff and landing.
Context Anchor
Seen in discussions of wing design, high-lift devices, takeoff, landing, and slow-flight handling.
Derivation
Named after Werner Krueger, the German aerodynamicist who developed the design in the 1940s while working at the Aerodynamische Versuchsanstalt in Göttingen. The spelling 'Kreuger' is a common variant of 'Krueger' seen in some FAA materials.
Why Pilots Care
They allow the wing to produce sufficient lift at lower airspeeds, reducing takeoff and landing distances and lowering stall speed.
Grounding Statement
Picture a panel near the front underside of the wing swinging out to make the wing act larger and more curved when the airplane is moving slowly.
Intuition Check
Do not read “leading” as “most important” here. It means the front edge of the wing, the part that reaches the air first.
Example Sentence 1
On the Boeing 747, the inboard Krueger flaps extend during takeoff to lower the stall speed and shorten the takeoff roll.
Example Sentence 2
On short-field takeoffs, deploying the leading edge flaps allowed the airplane to become airborne at a lower groundspeed.