droop
A hinged portion of the leading edge of an aeroplane's wing, which swivels downward to increase lift during takeoff and landing.
droop: wing leading edge flap for low-speed lift
A droop is a hinged surface mounted on the leading edge of a wing, positioned inboard of the slats and ahead of the main wing structure. During takeoff and landing, it rotates downward by a fixed angle, typically 5 to 15 degrees depending on the aircraft type, to increase the wing's camber and generate additional lift at low airspeeds when the aircraft cannot rely on high velocity over the wing.
Unlike slats, which slide forward and create a slot to delay stall, droops increase curvature without moving spanwise. The droop is mechanically simpler: it pivots on a hinge line and is driven by hydraulic actuators or, on smaller aircraft, cables connected to the flight control system. Once airborne and the aircraft accelerates, the droop retracts flush with the leading edge to restore the wing's cruise aerodynamic profile and reduce drag.
Variants and operation
Some aircraft use droops only on the inboard wing sections; others extend them across the entire leading edge. On turboprops and regional jets, droops often work in concert with leading edge slats: the droop handles the initial angle-of-attack increase during the takeoff roll and climb-out, while slats may deploy separately at higher angles. The droop typically moves as a single unit controlled by a flight deck switch or, on modern aircraft, automatically via the flight control computer.
Maintenance focuses on hinge wear, actuator rod corrosion, and rigging drift. A droop that does not return to cruise position cleanly will create an asymmetric drag penalty and handling imbalance. Accumulated ice on the leading edge can jam the droop mechanism, so anti-ice fluid application and thermal anti-ice systems are standard on commercial aircraft. Technicians verify droop position at each preflight and confirm actuator pressures during periodic inspections.
The term droop reflects the literal action: the surface droops, or hangs down, rather than slides or extends. In aerospace parlance, droops sit lower in the hierarchy than slats and flaps because they contribute less total lift increase but serve a complementary role in the low-speed envelope. Their presence on an airframe is often transparent to pilots and passengers but essential to ensuring safe takeoff and landing performance, particularly from short fields or in hot-and-high conditions.