NAS1921M05S04WU - Dassault OEM Blind Rivet

NAS1921M05S04WU – Dassault OEM Blind Rivet

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The NAS1921M05S04WU is a high-performance, flight-critical structural blind rivet, primarily utilized as an OEM fastener for Dassault Aviation airframes. As part of the NAS1921 series, this component is a "Bulbed Cherrylock" style fastener, engineered for applications where access to the "bucking" side of the structure is impossible. The NAS1921M05S04WU is specifically designed to provide high shear and tensile strength in thin-gauge materials, utilizing a mechanically locked spindle that ensures the rivet remains vibration-proof throughout the aircraft's pressurized flight cycles.

The "WU" suffix denotes a specialized finish or lubricant requirement typical of Dassault’s stringent corrosion-control and assembly standards. Unlike standard blind rivets, the NAS1921 series features a large, "bulbed" blind-side upset that provides a wide bearing surface, making it ideal for joining composite-to-metal or thin-skinned aluminum structures. This rivet is essential for structural repairs and assembly on Dassault Falcon business jets, where aerodynamic smoothness and structural weight-to-strength ratios are prioritized.

Key Features

• Mechanically Locked Spindle: Features a positive locking ring that prevents the mandrel from vibrating loose, ensuring the rivet maintains its structural integrity under the high-acoustic and mechanical vibrations of turbine operations.

• Large Bulbed Upset: During installation, the sleeve deforms into a broad, bulb-shaped footprint on the blind side, distributing the load across a wider area to prevent "pull-through" in thin or fragile materials.

• High-Strength Monel/Stainless Steel Construction: Manufactured from corrosion-resistant materials (typically Monel or A-286 CRES) to withstand the galvanic environment of the airframe without the need for additional wet-sealing in many applications.

• Universal Head Profile: The protruding head design provides a robust bearing surface for the primary structure, ensuring maximum joint clamp-up.

• Controlled Stem Break: Engineered for a clean flush-break, minimizing the need for secondary "shaving" or finishing operations, thus reducing maintenance man-hours.

Technical Specifications

• Part Number: NAS1921M05S04WU

• Manufacturer: Dassault OEM / Cherry Aerospace (Licensed)

• Fastener Type: Blind Rivet, Bulbed, Mechanically Locked Spindle

• Diameter: 5/32" (0.156 inch) nominal (denotes the "05" code)

• Grip Range: 0.188 – 0.250 inch (denotes the "04" code)

• Material (Sleeve): Monel (Nickel-Copper Alloy) or CRES

• Material (Mandrel): Stainless Steel

• Head Style: Universal (Protruding)

• Finish/Lubricant: Specialized "WU" code (Typically denotes a specific chemical conversion coating or dry-film lubricant per Dassault specifications)

• Governing Specification: NAS1921 / MIL-HDBK-5

Aircraft Compatibility

• Dassault Falcon Series: 10, 20, 50, 900, 2000, 7X, and 8X.

• Military Rafale/Mirage: Secondary structural applications.

• Note: Structural fasteners must be verified against the specific Dassault Structural Repair Manual (SRM) or Illustrated Parts Catalog (IPC) for the effectivity of your airframe serial number.

Applications

The NAS1921M05S04WU is utilized for Primary and Secondary Structural Fastening in "blind" areas. Specific applications include:

• Fuselage Skin Repair: Patching and doubling in areas where internal frames or systems prevent bucking bar access.

• Leading Edge Slat Assemblies: Securing components where high vibration resistance is required.

• Avionics Shelf & Bracketry: Providing high-strength attachment points within pressurized compartments.

Why Choose NAS1921M05S04WU?

Using the exact Dassault-specified NAS1921M05S04WU is critical for maintaining the fatigue-life certification of the airframe. Standard commercial rivets lack the interference-fit properties and the mechanical locking ring of the NAS1921 series. A non-conforming fastener may lead to "smoking rivets" (evidence of fretting) or localized structural cracking due to improper load transfer. The "WU" specification ensures compatibility with Dassault’s proprietary assembly lubricants, preventing stress corrosion cracking (SCC) in the fastener bore.

The mechanical performance of the NAS1921M05S04WU is rooted in the physics of plastic deformation and interference fitting. During the pull-cycle, the mandrel head is drawn into the rivet sleeve, causing it to expand and fill the hole entirely—a process known as hole-filling. This creates a "frictional lock" that assists in load transfer across the joint. As the mandrel reaches its predetermined break-load, the locking ring is "swaged" into the groove of the mandrel, creating a permanent, mechanical obstruction that prevents the mandrel from migrating. The Monel (Nickel-Copper) sleeve is specifically chosen for its galvanic compatibility with aluminum alloys; it possesses a mid-range electrochemical potential that minimizes the risk of bimetallic corrosion, which is essential for the long-term structural health of high-utilization turbine aircraft.

Note: This is a structural, flight-critical fastener. Installation must be performed using the correct Cherry Aerospace (or equivalent) pneumatic puller with the specified nose-piece for 5/32" NAS1921 fasteners. Verify hole size with a "Go/No-Go" gauge prior to installation. Installation must be performed by a certified A&P/IA mechanic in accordance with the Dassault Structural Repair Manual (SRM).

Documentation

• NAS1921 Standard - National Aerospace Standards Committee

• Cherry Aerospace - Cherrylock Bulbed Rivet Technical Data

• No public-facing Dassault proprietary "WU" lubricant specification was located; refer to the Dassault SRM for chemical compatibility.

Description:   Rivet, Blind
Part Number:   NAS1921M05S04WU


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