Also called flap peening or flap peen — the same process, governed by AMS 2590.
Flapper peening is a manual peening process using a rotary tool fitted with flexible flaps coated with tungsten carbide or sintered steel particles. The operator applies the tool tangentially to the surface at a controlled rotation speed (2,000-5,000 rpm) and constant pressure.
The mechanical effect is equivalent to conventional shot peening: surface plastic deformation, generation of residual compressive stresses, fatigue life improvement. What makes flapper distinctive is its ability to operate in complex geometries, confined areas, or directly on the aircraft during line maintenance — where an automated peening booth cannot be used.
Flapper peening is specified by AMS 2590 (Rotary Flap Peening of Metal Parts). Process qualification requires an Almen-strip intensity curve, renewed operator qualification and batch-level traceability of flapper heads.
Flapper peening — also commonly called flap peening in shop-floor usage and specifications — refers to the same process: both terms are interchangeable. Kronos also supplies flap peening machines, rotary tools and consumables (carbide flaps, mandrels) in addition to execution and training.