Krueger flap

Unlike slats or droop flaps, the main wing upper surface and its leading edge is not changed.

Also, when deployed, Krueger flaps result in a much more pronounced blunt leading edge on the wing, helping to achieve better low-speed handling.

[2] The Krueger flaps developed for the Boeing 747 were constructed from fiberglass material and were designed to be intentionally distorted into a much more efficient aerofoil section on deployment.

[7] The flap was added to prevent wing stall with an extreme attitude take-off with the tail dragging on the runway, a scenario that had caused two de Havilland Comet accidents.

[10] The left wing was modified to include a 6.7 m-span glove section supporting a variable-camber Krueger flap to be deployed during landing, protruding just ahead of the leading edge.

The test flights were supported by the European airline group TUI AG and conducted jointly with NASA as part of the agency’s Environmentally Responsible Aviation (ERA) program.