The leading-edge droop flap is a device on the

leading edge The leading edge is the part of the wing that first contacts the air;Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 305. Aviation Supplies & Academics, 1997. alternatively it is the foremost edge of an airfoil sectio ...

of aircraft wings designed to improve airflow at high angles of attack. The droop flap is similar to the

leading-edge slat A slat is an aerodynamic surface on the leading edge of the wing of a fixed-wing aircraft. When retracted, the slat lies flush with the rest of the wing. A slat is deployed by sliding forward, opening a slot between the wing and the slat. Air from ...

and the

Krueger flap Krueger flaps, or Krüger flaps, are lift enhancement devices that may be fitted to the leading edge of an aircraft wing. Unlike Leading-edge slat, slats or leading-edge droop flap, droop flaps, the main wing upper surface and its leading edge is ...

, but with the difference that the entire leading edge section rotates downwards, whereas the slat and Krueger flap are panels which move away from the wing leading edge when it is deployed.Norris & Wagner (2005), pp.67-68

Location

A leading-edge droop flap comprises the rounded front part of a wing, in movable form. The

Airbus A380 The Airbus A380 is a very large wide-body airliner, developed and produced by Airbus until 2021. It is the world's largest passenger airliner and the only full-length double-deck jet airliner. Airbus studies started in 1988, and the pr ...

has droop flaps between the fuselage and each inboard engine, at the leading edge of the thickest part of each wing. Early variants of the

Hawker Siddeley Trident The Hawker Siddeley HS-121 Trident (originally the de Havilland DH.121 and briefly the Airco DH.121) is a British airliner produced by Hawker Siddeley. In 1957, de Havilland proposed its DH.121 trijet design to a British European Airways (BEA ...

had two droop flaps on the outboard of each wing and a

on the section closest to the fuselage.''Flight International'' 29 June 1972, p.933
retrieved 7 March 2014

Use and effect

Droop flaps function with other high-lift devices on an aircraft to increase the camber of the wing and reduce the

stalling speed In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack exceeds its critical value.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', p. 486. Aviation Supplies & Academics, 1997. ...

. On the Airbus A380, the first stage of lift device selection deploys the droop flaps (called ''droop noses'' by Airbus) and leading-edge slats located further out on the wing; with the main flaps starting to extend when the second stage is selected. The variable sections on the A380 may be drooped to a position 22 or 25 degrees lower than their stowed position.Norris & Wagner (2005), p.155 Another function of droop flaps on the A380 is to change the stall characteristics of the wing. The A380's designers found that the airflow between the engines was separating from the wing surface prior to the airflow between the engine and the fuselage, an undesirable characteristic. Adding droop between the engine and the fuselage fixed the problem; whereas using a leading-edge slat would not have done so because of the gap (or slot) created between a slat and the wing when a slat is deployed.Norris & Wagner (2005), p.67

Aircraft with droop flaps

Airbus A350 The Airbus A350 is a flight length, long-range, wide-body twin-engine airliner developed and produced by Airbus. The initial A350 design proposed in 2004, in response to the Boeing 787 Dreamliner, would have been a development of the Airbu ...

Dassault Falcon 20 The Dassault Falcon 20 is a French business jet developed and manufactured by Dassault Aviation. The first business jet developed by the firm, it became the first of a family of business jets to be produced under the same name; of these, both t ...

Mikoyan-Gurevich MiG-23 The Mikoyan-Gurevich MiG-23 (; NATO reporting name: Flogger) is a variable-sweep wing, variable-geometry fighter aircraft, designed by the Mikoyan, Mikoyan-Gurevich OKB, design bureau in the Soviet Union. It is a third-generation jet fighter, ...

Northrop F-5 The Northrop F-5 is a family of supersonic light fighter aircraft initially designed as a privately funded project in the late 1950s by Northrop Corporation. There are two main models: the original F-5A and F-5B Freedom Fighter variants, and th ...

References

Notes

Bibliography