trailing edge

The trailing edge is the rear boundary of any airfoil, where the upper and lower surfaces meet and air flow finally departs the wing. In fixed-wing aircraft, this is typically a sharp line running spanwise (tip to root), though on some designs it may be slightly rounded or fitted with a beveled or knife-edge profile. On a typical transport wing, the trailing edge sits 15 to 20 percent of the wing's chord length back from the leading edge, though this ratio varies with airfoil design and speed regime.

The trailing edge must be kept in precise aerodynamic condition because flow separation occurs there first. Any damage, dent, or misalignment creates a discontinuity that trips vortex shedding and increases drag; severe damage can cause flutter or stall behavior at lower angles of attack than designed. For this reason, most maintenance schedules specify periodic inspection and measurement of trailing edge shape, especially after impact or hard landings.

Flaps, tabs, and hinged surfaces

The trailing edge is where moveable flight control surfaces attach: trailing edge flaps, ailerons, and elevators hinge along the trailing edge line. These control devices typically occupy 25 to 40 percent of the span or chord. The gaps and fairings around these surfaces are critical worry points; worn hinge brackets, loose fasteners, or missing seal tape allow air to leak into cavities, raising drag and reducing control authority. On high-speed aircraft, trailing edge cove pressure can drop enough to cause local Mach effects or noise problems if gaps are too large.

Materials at the trailing edge reflect speed and stress. On aluminum aircraft, the trailing edge skin is often 0.025 to 0.063 inches thick and may be skins riveted to a spar or to a structure of thin ribs and stringers. Composite aircraft trailing edges are typically laminated carbon or glass fabric in a resin matrix, with core material (foam or honeycomb) sandwiched between outer plies. Both types are prone to fatigue cracking and delamination in the bond line where the upper and lower skins meet.

Repair or replacement of a trailing edge section requires careful attention to aerodynamic shape. Trailing edge is typically not field-welded or hot-riveted on pressurized aircraft because the assembly is thin and close to fuel tanks; bonded patches or scarf-joint repairs are more common. Post-repair, trailing edge shape is verified using edge finders, depth gauges, or laser scanning to ensure the repaired section matches the original airfoil profile within tolerance, usually 0.06 inches or tighter depending on the operator's standards.