buffet

Buffet is the rapid, rhythmic vibration transmitted through an aircraft's structure when airflow separates from the wing surface during a stall or near-stall condition. The pilot feels it as a shaking or rumbling, typically in the control stick or yoke, though it can be felt throughout the cabin. It serves as an aerodynamic warning: the wing is no longer generating smooth lift, and the aircraft is approaching a dangerous flight regime.

The phenomenon occurs because smooth airflow over a wing is necessary for generating lift through pressure differential. As the aircraft slows or pitches up too steeply, the angle of attack exceeds the wing's critical value, usually between 15 and 20 degrees depending on the aircraft type and loading. The boundary layer separates from the upper surface, creating a turbulent wake. This separation is not steady; vortices form and break away intermittently, creating oscillating forces that propagate through the airframe.

Detection and Measurement

Pilots recognize buffet as a distinctive shaking that is harder and faster than turbulence from weather. Modern aircraft have buffet onset indicators and stick shakers, mechanical devices that vibrate the control column to alert pilots when approached stall speed is near. In the maintenance hangar, buffet characteristics are verified during envelope expansion testing of new aircraft types, where instrumented test flights map the speed and altitude at which buffet begins for different configurations and weights.

Buffet intensity varies with airspeed, altitude, weight, and center of gravity. At high altitudes where air is thin, buffet onset speed may be very close to the aircraft's maximum speed, creating a narrow flight envelope. Some aircraft experience transonic buffet, caused by shock waves forming on the wing at high subsonic speeds, which is a different aerodynamic phenomenon but produces similar vibration.

Ground crews and flight test engineers monitor buffet margins as part of performance validation. Excessive or premature buffet can indicate control surface damage, rigging errors, or contamination such as ice or insect residue on the leading edge. Buffet complaints from flight crews are taken seriously because they suggest the aircraft is operating closer to its aerodynamic limits than intended.