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Fuselage Frame Lugs

Name: Structural Lugs & Aircraft Fuselage Frame Interfaces – Frigate
Price: 249.00 USD
Availability: InStock

Fuselage frame lugs are vital load-transfer points between longitudinal members and circumferential frames. Their design directly affects load path continuity, joint stiffness, and fatigue resistance within the fuselage shell.

Material Specification

Titanium 6Al-4V (Grade 5), Aluminum 7075-T7351, or Maraging Steel (AMS 6514)

Mounting Points/Hole Pattern

2–4 bolt holes (NAS/AN/MS standards), Clevis pin bore (Ø6–25mm, H7 tolerance)

Load Path Geometry/Bearing Area

Optimized fillet radii (5–10mm), Bearing area ≥2x pin diameter (Per MIL-STD-1312)

Load Capacity

Ultimate Tensile – 900–1,400 MPa, Bearing Strength – 1,200–2,000 MPa, Shear Load – 50–150 kN

Deflection Limits

≤0.2mm deflection @ design limit load, Natural frequency >100 Hz

Product Description

Poorly designed or machined lugs can create stress discontinuities, leading to localized overstress, fretting, and eventual crack initiation—compromising structural integrity over time.

Surface Treatment

Anodizing (Aluminum), Passivation (Titanium), Cadmium Plating (Steel, per AMS-QQ-P-416)

Dimensional Tolerances

±0.025mm (Bore diameter), ±0.05mm (Hole positions), Surface flatness ≤0.05mm

Non-Destructive Testing Requirements

Fluorescent Penetrant (FPI), Ultrasonic Testing (UT), X-ray (RT for welds)

Certification Standards

AMS 4911 (Ti-6Al-4V), BMS 7-260 (Aluminum), FAA 14 CFR §25.571, AS9100

Fatigue Life

10⁶ cycles @ 50% UTS (Validated per ASTM E466), S-N curve provided

Technical Advantages

Material integrity directly influences long-term service performance, especially under cyclic pressurization and maneuver loading. Aerospace-grade aluminum alloys such as 7050-T7451 and titanium alloys like Ti-6Al-4V are selected based on their fatigue crack growth thresholds, fracture toughness, and compatibility with adjacent structural elements. Grain flow orientation is preserved through die forging or precision closed-die methods to improve resistance to initiation fatigue. Material selection also considers the environmental operating envelope, including resistance to corrosion in high-humidity or salt-laden atmospheres, ensuring compatibility with dissimilar metals in hybrid assemblies.

Dimensional tolerances are maintained to strict aerospace standards, typically within ±0.01 mm on critical features such as bore diameter, face-to-face thickness, and hole center locations. Multi-axis CNC machining with tool path compensation and thermal stability monitoring ensures repeatable output across batch production. Final inspection utilizes contact coordinate measurement systems (CMM) with calibrated reference geometries to validate tolerance bands and geometric true position. Positional accuracy of holes relative to datum references supports seamless integration into pre-drilled airframe sections, eliminating field rework.

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Industry Applications

Primary Load Path Joints

Used at fuselage ring frame intersections to transfer axial and bending loads from longerons, floor beams, and keel structures.

Landing Gear Load Transfer Points

Integrated into lower fuselage structures to handle concentrated landing gear forces and distribute them into surrounding structural frames.

Wing-Fuselage Interface Brackets

Applied at wing box mating zones to provide rigid mechanical linkage between wing spars and fuselage frames under bending moments.

Pressure Bulkhead Attachments

Used in joints around aft or forward pressure bulkheads to maintain structural integrity under cabin pressurization load cycles.

Payload Integration Lugs

Support structural attachment of modular payload systems in military or cargo aircraft where high-load localized transfer is required.

Helicopter Pylon Mounting Nodes

Serve as mechanical interface between rotor pylon assemblies and upper fuselage structures subjected to torsional and dynamic loads.

Surface Treatment and Corrosion Mitigation

Surface durability is enhanced through post-machining treatments including anodizing, shot peening, and cadmium or zinc-nickel plating, selected based on the base material and the environmental exposure class of the fuselage zone. These treatments reduce surface micro-cracks, enhance compressive surface stress states, and prevent galvanic interaction with adjoining metallic assemblies. Peening coverage and intensity are qualified through Almen strip validation. Coating adherence is verified by salt spray resistance and thickness measurements in accordance with MIL and AMS specifications.

Fuselage frame lugs are subject to fatigue qualification protocols simulating millions of load cycles replicating operational stress spectra. Test specimens are instrumented with strain gauges and subjected to spectrum loading under hydraulic test rigs to validate predicted life performance. The fatigue design limit is established using crack initiation thresholds, and fracture mechanics analysis is conducted to assess damage tolerance. All testing is conducted per ASTM E466 and E647 standards, and data is correlated with FEA-predicted stress intensity factors (K-values) for certification evidence.

Having Doubts? Our FAQ

Check all our Frequently Asked Question

How does Frigate ensure bore concentricity in fuselage frame lugs used for fuselage frame joints?

Frigate uses multi-axis CNC machines with real-time positional feedback and thermal compensation to maintain concentricity below 0.01 mm. Bore alignment is verified using coordinate measuring machines (CMM) referenced to primary datums. This ensures the lug fits with bushings or pins without inducing eccentric loads. Consistent concentricity improves load distribution and enhances fatigue life of the assembled structure.

What makes Frigate’s fuselage frame lugs suitable for high-cycle fatigue environments?

Frigate fabricates lugs from aerospace-grade forgings with directional grain flow aligned to principal stress paths. Post-machining, the fuselage frame lugs undergo shot peening to introduce compressive surface stresses that resist crack initiation. Surface finishes are controlled within tight Ra limits to eliminate micro-notches. Each batch is fatigue-tested to validate endurance performance per MIL-STD-1530.

How does Frigate control metallurgical integrity during lug production?

Frigate sources pre-certified billets or forgings with full material test reports (MTRs) and ultrasonic inspection. Heat treatment is performed in AMS-compliant furnaces with controlled quench rates and validated cycle parameters. Microstructure is evaluated for grain size, phase distribution, and inclusions using ASTM E112 and E45. This ensures the fuselage frame lugs meet strength, ductility, and fracture toughness requirements.

What testing protocols does Frigate use for lugs installed in pressure bulkhead zones?

Frigate follows ASTM E1444 for magnetic particle inspection and AMS 2631 for ultrasonic evaluation on critical pressure zone lugs. Stress-corrosion susceptibility is tested using ASTM G47 or alternate environment simulation protocols. Load testing is performed using axial and shear rigs simulating aircraft pressurization cycles. All results are documented and traceable to the part’s unique ID.

How does Frigate support rapid design changes for custom fuselage frame lug requirements?

Frigate integrates CAD-driven CAM systems to quickly adapt geometry and toolpaths to revised customer drawings. Finite Element Analysis (FEA) is used to evaluate new designs for stress concentration and fatigue hot spots. Rapid prototype machining with in-house tooling minimizes lead time. Full PPAP and FAI documentation are generated within accelerated engineering cycles.

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LOCATIONS

Registered Office

10-A, First Floor, V.V Complex, Prakash Nagar, Thiruverumbur, Trichy-620013, Tamil Nadu, India.

Operations Office

9/1, Poonthottam Nagar, Ramanandha Nagar, Saravanampatti, Coimbatore-641035, Tamil Nadu, India. ㅤ

Other Locations

GENERAL ENQUIRIES

FRIGATE is a B2B manufacturing company that facilitates New Product Development, contract manufacturing, parallel manufacturing, and more, leveraging its extensive partner networks.

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