Leading edge

Lore & Background

The structural leading edge may be equipped with one or more of the following: leading edge boots, leading edge cuffs, leading edge extensions, leading edge slats, leading edge slots, Krueger flaps, stall strips, and vortex generators. Associated terms are leading edge radius and leading edge stagnation point. Seen in plan the leading edge may be straight or curved. A straight leading edge may be swept or unswept, the latter meaning that it is perpendicular to the longitudinal axis of the aircraft. As wing sweep is conventionally measured at the 25% chord line an unswept wing may have a swept or tapered leading edge. Some aircraft, like the General Dynamics F-111, have swing-wings where the sweep of both wing and leading edge can be varied.

In high-speed aircraft, compression heating of the air ahead of the wings can cause extreme heating of the leading edge. Heating was a major contributor to the destruction of the Space Shuttle Columbia during re-entry on February 1, 2003. The term leading edge also applies to sailboats: when sailing into the wind, the dynamics that propel a sailboat forward are the same that create lift for an airplane. The term leading edge refers to the part of the sail that first contacts the wind. A fine tapered leading edge that does not disturb the flow is desirable since 90% of the drag on a sailboat owing to sails is a result of vortex shedding from the edges of the sail.

Reader's Guide

The leading edge is notable for its dual definition—aerodynamic and structural—which can diverge in flight regimes such as a tailslide, where the aerodynamic leading edge becomes the trailing edge while the structural leading edge remains unchanged. This distinction is fundamental to understanding wing behavior. The structural leading edge can host various devices—boots, cuffs, extensions, slats, slots, Krueger flaps, stall strips, and vortex generators—each modifying airflow or structural properties. Its planform can be straight or curved, with straight leading edges either swept or unswept; sweep is conventionally measured at the 25% chord line, so an unswept wing may still have a swept leading edge. Variable-sweep wings, as on the General Dynamics F-111, allow the leading edge sweep to change in flight. In high-speed flight, compression heating of the air ahead of the wings can cause extreme heating of the leading edge, a factor that contributed to the destruction of the Space Shuttle Columbia. The concept extends to sailboats, where the leading edge of the sail is the part first contacting the wind, and a fine tapered shape is desirable to reduce drag from vortex shedding, which accounts for 90% of sail-induced drag. Designers have experimented with aerodynamically shaped masts, rotating masts, wing masts, or mast-aft rigs to improve performance.