Manual Process — Hard-to-Reach Areas — 24/7 AOG

Flapper
Peening

Processes — Flapper Peening

Manual peening using flexible flaps. Ideal for hard-to-reach areas, localized repairs, on-wing line-maintenance interventions. AMS 2432 / AMS 2546 compliant.

Applicable standards

SAE J442SAE J443AMS 2546

Related industries

How it works

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 2432 (manual shot peening) and AMS 2546 (aerospace flapper peening). Process qualification requires an Almen-strip intensity curve, renewed operator qualification and batch-level traceability of flapper heads.

Typical applications

Landing gear sockets and cavities

Fatigue initiation zones hard to reach with conventional shot peening. Applicable on removed or assembled parts.

Aircraft structural repairs (Major Repair)

After adding doublers, patches or crack repair — peening applied within the repair file.

AOG — on-wing intervention

Aircraft on Ground: immediate repair of critical zones on an aircraft on the tarmac or in a hangar. Our AOG team is on call 24/7.

Wing underside and composite-adjacent zones

Controlled peening near composites where a conventional blaster is not admissible.

Life restoration after operational use

On military structures (armored vehicles, fighter aircraft) after intensive missions, before returning to operation.

Repair of cracks detected during scheduled inspection

After detection and mechanical rework of a crack, local peening to delay re-initiation.

Parameters by material

Parameter	Typical value
Flapper rotation speed	2,000 to 5,000 rpm
Flapper diameter	8, 12 or 16 mm depending on zone
Zone exposure time	30-120 s depending on target intensity
Equivalent Almen intensity	6 to 14A
Minimum coverage	100% (visual check, 10× loupe)

Flapper peening is effective on most aerospace alloys: aluminum (2024, 7075), titanium (Ti-6Al-4V), steels (300M, 4340, stainless), superalloys (Inconel under specific conditions). Flapper configuration (grit, binder) is selected according to the material.

Frequently asked questions

Does flapper peening produce the same residual stresses as automated shot peening?+

Yes, at equivalent stress depth. SAE studies (J2277, J2597) and Airbus/Boeing qualifications show that flapper peening reaches the same compressive residual stress levels as conventional shot peening for equivalent Almen intensities.

What is the minimum qualification for a flapper-peening operator?+

SAE J2277 level 2 minimum, with additional flapper-peening qualification. Kronos operators are all level 2 or level 3, with AOG field experience and multi-OEM exposure.

Can flapper peening be done on composite?+

Not directly on composite. However, flapper is ideal on metallic structure adjacent to composite, thanks to its precise control that avoids particle projection.

How long does a typical AOG flapper-peening intervention take?+

For an aerospace AOG, between 4 and 12 hours of net treatment depending on the zone. End-to-end lead time (travel + intervention + documentation): 24 to 48 hours from the call.

How is intensity controlled in flapper peening?+

Through an Almen strip exposed at the start and end of the intervention, under the same parameter conditions as the actual treatment. Saturation is established upstream for every tool/material/target-intensity combination.

FlapperPeening