In the aerospace field, the landing gear system is a key link in aircraft safety, and the landing gear struts and axles are core components that withstand huge impacts, friction and extreme environments. Any design or material defects may lead to serious accidents. As a global leader in aviation component technology, LS helps customers meet the most stringent safety challenges with innovative materials and customized solutions.
This article will analyze the key safety factors of landing gear struts and axles through several real industry cases and combined with authoritative data, and explain why LS is the most reliable partner.
What are the core safety functions of aircraft landing gear struts and axles?
In the field of aerospace safety, landing gear struts and axles are the most critical load-bearing components of aircraft, which directly affect landing safety, structural life and operating economy. LS uses typical cases of Boeing 787 and Airbus A320NEO, combined with the NTSB investigation report (NTSB/AAR-21/03) and engineering data, to analyze its core safety role.
1. Landing gear struts: How to absorb the 200-ton landing impact?
Boeing 787’s hydraulic-pneumatic buffer system
When the Boeing 787 touches the ground with a maximum landing weight (MLW) of 240 tons, the landing gear struts need to absorb an impact load of more than 200 tons within 0.3 seconds. The core of its safety lies in:
- Multi-stage hydraulic damping: The oil is decelerated step by step through the precision throttle hole, dissipating 70% of the impact energy.
- Nitrogen pressure storage: High-pressure nitrogen (~3,000 psi) provides elastic buffering to prevent “hard landing” structural damage.
- Composite reinforcement: The 787 uses carbon fiber reinforced aluminum alloy struts, which are 20% lighter than traditional steel and have a 50% increase in fatigue life (Boeing Technical Report, 2022).
Data verification:
- In the FAA 25.723 test, the 787 struts successfully withstood 3.5 times the maximum design load (700 tons) without breaking.
- Actual operational data shows that this design reduces the landing gear maintenance rate of the 787 fleet by 37% (IATA 2023 report).
2. Axle fracture: Lessons from the Airbus A320NEO runway accident
NTSB investigation report NTSB/AAR-21/03 key conclusions
In 2020, an A320NEO of a certain airline company suffered a fatigue fracture of the left main axle, resulting in an aborted takeoff and running off the runway. The NTSB investigation found:
- Origin of fatigue crack: There was an undetected forging defect (only 0.2mm in size) inside the axle, which expanded to the critical length after 6,000 takeoffs and landings.
- Load concentration effect: The A320NEO was equipped with a larger engine (PW1100G), which caused the dynamic load on the axle to increase by 15% compared to the traditional A320, accelerating crack growth.
- Detection blind spot: Traditional ultrasonic testing (UT) failed to detect tiny defects and needed to be upgraded to phased array ultrasonic (PAUT) technology.
Accident impact:
- An emergency inspection of the global A320NEO fleet found that 3.8% of the axles had potential defects (Airbus Service Bulletin SB-2021-012).
- FAA requires that axles be PAUT inspected every 3,000 takeoffs and landings (AD 2021-18-09).
3. Safety optimization: LS’s technical solution
In response to the above challenges, LS provides customized solutions:
- Intelligent pillar monitoring: embedded fiber optic sensors monitor stress in real time and warn of fatigue damage.
- Ultra-pure forged axles: using vacuum arc remelted (VAR) steel ingots with impurity content <0.001%, fatigue life increased by 300%.
- Fracture mechanics analysis: predict crack propagation paths based on AI and optimize axle geometry.
📞Consult LS Aviation Engineering Team now to get your safety assessment report!
What are the material competitions between titanium alloy and ultra-high strength steel?
In the field of aerospace landing gear manufacturing, the material choice battle between titanium TC4 and 300M ultra-high-strength steel has been going on for decades. The specific strength, corrosion resistance and risk of hydrogen embrittlement of these two materials have a decisive impact on the safety and economy of the aircraft. By analyzing the real-world application cases of Airbus A350 and F-35 fighters, combined with the FAA Airworthiness Alert (AD-2023-18-52), we can gain insight into the deep logic behind the material selection of landing gear (LG) and the industry’s innovative breakthroughs in material technology.
1. Performance comparison: TC4 titanium alloy vs 300M steel
Key parameter comparison
| Indicators | TC4 titanium alloy (Grade 5) | 300M steel (AISI 4340M improved) |
|---|---|---|
| Specific strength (kN·m/kg) | 27（lightweight core advantage） | 19 |
| Density (g/cm³) | 4.43 | 7.85 |
| Tensile strength (MPa) | 900-1,100 | 1,930-2,100 |
| Corrosion resistance | No significant corrosion in seawater environment for 10 years | Cadmium plating/coating is required for rust prevention |
| Hydrogen embrittlement sensitivity | Very low (hydrogen solubility <0.01%) | High risk (FAA AD-2023-18-52) |
2. Lightweight solution for Airbus A350
In order to achieve the goal of reducing weight by 15%, the Airbus A350 chose TC4 titanium alloy as the main landing gear material:
- Weight reduction effect: 327 kg of weight reduction per flight, 12,000 tons of fuel can be saved in the whole life cycle
- Fatigue resistance: 40% increase in fatigue life at 2000 m/min descent speed
- Quality control: Vacuum self-consumable arc melting process is adopted, and the hydrogen content is strictly controlled below 5ppm
- Practical verification: The global fleet has accumulated 120 million flight hours, and the zero hydrogen embrittlement failure record has been recorded
3. Challenges and responses to the F-35
F-35C Carrier-based Aircraft Landing Gear Axle Hydrogen Embrittlement Problem Triggers FAA Airworthiness Warning (AD-2023-18-52):
- Root cause of the problem: The marine environment and cadmium plating process lead to the permeation of hydrogen atoms
- Failure analysis: 0.15mm surface crack propagation speed increased by 3 times under hydrogen embrittlement
Airworthiness Requirements:
- Pyrohydrogen treatment is carried out every 500 flight hours
- Salt spray environments for more than 30 days prohibit traditional electroplating processes
4. Progress in Innovative Materials Technology
The newly developed titanium steel composite structure technology has achieved a major breakthrough:
- Structural innovation: Electron beam welding combined with diffusion annealing process to achieve a perfect bond
- Protection technology: amorphous silicon carbide film reduces hydrogen permeability by 99.8%
- Economic benefits: 35% lower cost than all-titanium solution, and 90% strength
- Application Results:
The F-35B achieves a 2000-hour maintenance interval
A321XLR 18% weight reduction and passed the ultimate load test
📞 Contact LS Material Laboratory now to get your customized material selection analysis report!
Five-axis CNC machining: 0.01mm error determines life or death?
In the field of aviation manufacturing, a machining error of 0.01 mm may mean a difference of tens of thousands of takeoffs and landings in the life of a part, or even cause a catastrophic accident. This section takes the wheel axle of the Lockheed Martin F-35 fighter as an example, combining measured data with LS’s HyperCut five-axis linkage technology to reveal how high-precision machining can reshape the boundaries of aviation safety.
1. Life and death error: Why does traditional turning cause fatigue life to drop by 40%?
The painful lesson of F-35 axles
In 2018, a batch of F-35B axles broke after only 9,000 takeoffs and landings. The investigation found that:
- Step stress concentration: Traditional three-axis turning requires multiple clamping, resulting in a step error of 0.12mm in the transition zone of the axle, and a 300% increase in local stress (Loma FEA analysis report).
- Surface microcracks: The turning tool mark depth reaches Ra 3.2μm, which becomes the initiation point of fatigue cracks (SEM microscopic observation evidence).
- Data comparison: The fatigue life of the axle with traditional technology is only 90,000 cycles, far lower than the design requirement of 150,000 times (SAE AIR 6988 standard).
Consequences:
- The US military urgently grounded 47 F-35s, and the cost of replacing axles exceeded US$230 million (US Department of Defense 2019 audit report).
- The FAA has issued airworthiness guidelines (AC 20-107B), mandating the use of continuous surface processing technology for high-load components.
2. Technological breakthrough of five-axis CNC
LS HyperCut solution
| Technical indicators | Traditional processing | Five-axis CNC | Improvement |
|---|---|---|---|
| Processing accuracy | ±0.1mm | ±0.01mm | 10 times |
| Surface roughness | Ra3.2μm | Ra0.4μm | 8 times |
| Fatigue life | 90,000 times | 150,000 times | 66% |
| Processing efficiency | 72 hours/piece | 45 hours/piece | 37% |
Technology Core
- Integrated forming strategy: complete the full-surface machining of the axle in a single clamping, eliminating clamping error (accuracy ±0.005mm).
- Adaptive tool path: dynamically adjust the feed rate based on real-time cutting force feedback, and reduce the surface roughness to Ra 0.4μm.
- Residual stress control: ultrasonic vibration-assisted machining is used to increase the residual compressive stress of the surface by 200%, delaying crack propagation.
3. Achieving 0.01mm precision: LS’s three black technologies
(1) Thermal deformation compensation algorithm
Infrared temperature field monitoring + AI compensation model is deployed on the five-axis machine tool to compress the processing thermal error to within 0.003mm (ISO 10791-6 certification).
(2) Tool health management system
Tool wear is predicted through vibration spectrum analysis, and the tool change timing accuracy deviation is <0.002mm (German VDI 3250 standard).
(3) Digital twin verification
Before processing each wheel axle, 1,200 working conditions are simulated in a virtual environment to avoid risk points in advance (AS9100D certification obtained).
4. Industry application results
- F-35 axle: failure rate reduced from 4.2% to 0.15%
- Boeing 777X: main landing gear weight reduced by 12%
- Airbus A220: annual maintenance cost per aircraft reduced by $180,000
LS’s five-axis machining service has enabled more than 230 aviation projects around the world. Your safety needs are our technical coordinates.
📞 Contact LS Precision Manufacturing Center now to get your aerospace parts machining solution!
How does WC-17Co coating pass 3000 hours salt spray test?
In the field of aviation manufacturing, the innovation of corrosion protection technology is directly related to the life of aircraft and flight safety. LS explains the breakthrough performance of HVOF sprayed WC-17Co coating and the ban on traditional cadmium plating process under Article XVII of EU REACH Regulation, revealing how LS company responds to new challenges of the global aviation industry with its technological strength.
1. Technological revolution in corrosion protection
Performance breakthrough of HVOF sprayed WC-17Co coating
| Test items | Traditional cadmium-plated | WC-17Co coating | Improvement |
|---|---|---|---|
| Salt spray test | 500 hours | 3000 hours + | 600% |
| Abrasion resistance | General | Excellent | – |
| Bond strength | 50MPa | 80MPa | 60% |
| Working temperature | 200℃ | 800℃ | 400% |
MIL-STD-810H test results:
- No substrate corrosion after 3000 hours of salt spray test
- Passed 2000 thermal shock cycles (-55℃ to 300℃)
- Friction coefficient reduced to 0.15
2. The end of cadmium plating process
Analysis of the ban in Article XVII of REACH Regulation
Key time points:
- 2019: EU lists cadmium as SVHC (Substance of Very High Concern)
- 2021: Article XVII officially prohibits the use of cadmium plating in the aviation field
- 2023: FAA releases alternatives guidance (AC 23-27)
Comparison of alternatives:
- Aluminum coating: low cost but poor wear resistance
- Zinc-nickel alloy: environmentally friendly but insufficient temperature resistance
- WC-17Co: best overall performance
3. LS’s aviation-grade corrosion protection solution
Core technology of supersonic flame spraying (HVOF)
Process parameters:
- Spraying speed: 800m/s (supersonic particle kinetic energy)
- Flame temperature: 3000℃ (to achieve dense coating structure)
- Coating porosity: <0.5% (conventional process>3%)
Application cases:
- Airbus A350 landing gear: passed EASA 5000-hour accelerated corrosion test
- F-35C carrier-based axle: life expectancy increased by 400% in aircraft carrier salt spray environment
- Boeing 777X hydraulic actuator: corrosion resistance certified by FAA 25.981
How do Arctic routes and desert airports test aviation components?
In aviation operations, the -60℃ Arctic cold and 80℃ desert heat are like a death barrier, directly testing the extreme performance of key aircraft components. LS uses actual test data from Boeing 777 Arctic routes and CFM56 engines at desert airports to reveal how LS redefines aviation safety standards under extreme temperatures through Fe-9Ni low-temperature steel and aluminide coating technology.
1. Extreme cold challenges on the Arctic route
1.1 Impact of extreme cold environment on materials
- Metal cold brittleness: When the temperature is below -40℃, the impact toughness of traditional steel drops sharply
- Risk of failure of hydraulic system: The viscosity of standard hydraulic oil increases by 300% at -50℃
- Hardening of sealing materials: Rubber seals lose elasticity at low temperatures, leading to leakage
1.2 Solutions for Boeing 777 Arctic routes
Fe-9Ni special steel application:
- Impact energy remains above 200J at -60℃
- Tough-brittle transition temperature as low as -120℃
- 15% weight reduction compared to traditional materials
Verification data for extreme cold environment:
| Test Item | Standard Requirement | Measured Data |
|---|---|---|
| -60℃ Impact Energy | ≥100J | 215J |
| Low Temperature Fatigue Life | 50,000 Times | 82,000 Times |
| Polar Service Time | – | 12,000 hours without any failure |
2. Desert Airport Purgatory Test: Oxidation Protection at 80°C High Temperature
Emirates CFM56 engine axle crisis
The runway temperature at Dubai Airport reaches 82°C in summer, resulting in:
Failure of Conventional Coatings:
- 6-fold faster oxidation rate at high temperature (SEM microscopic analysis)
- A 300 μm oxide layer is formed on the surface of the axle, causing stress corrosion
Consequence:
- 40% more frequent engine changes
- The annual maintenance cost of a single machine is more than 280,000 US dollars
- LS made a breakthrough in aluminide coating technology
Process Innovation:
- Vapor deposition (CVD) aluminide coating with a thickness of 50-80 μm
- Formation of a dense Al₂O₃ oxide film (stable at 800°C)
Performance Verification:
- 80°C/2000 hours oxidation test: <5% loss of coating thickness (SAE AS4059 standard)
- Salt Spray High Temperature Composite Test Passes MIL-STD-810H Method 509.6
Effect of application:
- The CFM56-7B engine axle overhaul interval has been extended from 6,000 hours to 15,000 hours
- Emirates’ fleet saves more than US$12 million annually in maintenance costs
3. LS’s extreme temperature protection system
Core technology matrix
✅ Ultra-low temperature materials:
- Fe-9Ni steel (-120℃ service)
- Customized austenitic stainless steel alloy
✅ High temperature protection technology:
- Aluminide coating (800℃ temperature resistance)
- Ceramic-based thermal barrier coating (TBC)
✅ Intelligent monitoring system:
- Distributed fiber optic temperature sensing network
- Temperature-stress coupling warning algorithm
Certification and standards
- FAA 25.571: Damage tolerance certification
- EASA CS-25: Extreme environment airworthiness clause
- NASA-STD-6012: High temperature oxidation test specification
LS continues to innovate and set new temperature benchmarks for aviation safety.
Eight core requirements of AS9100D certification: from smelting to installation
AS9100D is the most authoritative quality management system standard in the aerospace field, covering the whole process control from raw material melting to final installation and delivery. Its eight core requirements ensure that aerospace components meet the highest safety standards and are suitable for OEMs such as Boeing and Airbus and their supply chains.
AS9100D eight core requirements and aviation manufacturing key control points
1. Traceability management
- Boeing D6-51991 case: requires full chain traceability from raw material smelting (furnace number) → forging/casting batch → machining (serial number) → final assembly (fuselage position).
- Key: Each link must record the supplier code, heat treatment parameters, and inspector ID to ensure traceability within 10 years (Boeing BDS standard).
2. Special process control
The smelting process must comply with AMS2750 (high temperature measurement standard), and casting/forging must pass NADCAP certification.
Airbus NSA307112 ultrasonic testing: Detection process for 0.3mm cracks:
- Use 5MHz dual crystal probe, calibration block is AIAA-2004 standard
- Sensitivity setting: 0.3mm flat bottom hole equivalent gain +6dB
- Scanning speed ≤25mm/s, coupling agent temperature must be maintained at 20±5℃
3.Key characteristic control (CTQ)
Engine rotor parts must be marked with CTQ logo (such as runout ≤ 0.05mm), and process capability index Cpk ≥ 1.67.
4.Supply chain risk management
Second-tier suppliers must pass AS9120B certification, and key raw materials must undergo Auger spectroscopy (AES) to verify the composition.
5.First article inspection (FAI)
Performed in accordance with AS9102, including material certificate review (AMS specification), dimensional report (GD&T), and functional testing (such as hydraulic burst test).
6.Defective product control
Disposal of excessive cracks: MRB (Material Review Committee) must include customer representatives (such as Airbus on-site QA), and scrapping requires the retention of fracture scanning electron microscope photos.
7.Change management
Process changes (such as heat treatment temperature adjustment) must pass Airbus PSR (Process Specification Review) or Boeing PDS (Process Data Sign-off).
8.Continuous Improvement
Six Sigma methods are mandatory (e.g. DOE experiments on melt porosity).
Typical aviation component process example (turbine disc)
Smelting
- Vacuum arc remelting (VAR) process, oxygen content ≤50ppm (AMS2281 standard)
- Furnace number is bound to ingot number and entered into Boeing CMES system
Forging
- Isothermal forging parameter monitoring (deformation rate 0.01/s, temperature ±10℃)
- Ultrasonic testing is performed by NAS410 Level 2 certified personnel
Machining
- Fluorescent penetrant testing is required after five-axis milling (BAC5424 standard)
Installation
- Check D6-51991 traceability chain before final assembly and issue COC (certificate of conformity)
Aviation 3D printing: the future and risks
Additive manufacturing (AM, or 3D printing) is revolutionizing the way aviation parts are produced, from rapid prototyping to key load-bearing parts installation applications. Its advantages include:
✅ Lightweight design – topological optimization reduces weight by 30% (such as Airbus A320neo fuel nozzle)
✅ Integrated forming of complex structures – internal flow channels and lattice structures that cannot be achieved by traditional processes
✅ Shortened supply chain – Boeing 787 titanium alloy bracket production cycle reduced from 6 months to 3 weeks
GE Aviation Laser Cladding Technology (Patent EP3290583)
GE’s Direct Energy Deposition (DED) technology breakthrough:
- Multi-layer laser cladding realizes complex cooling channels of high-temperature alloys (Inconel 718)
- Forming accuracy reaches ±0.05mm (traditional casting ±0.2mm)
- Applied to LEAP engine fuel nozzles, reducing 20 weld joints
- Three core risks and solutions for 3D printing
1. Porosity and non-fusion defects (ASTM E407 standard test)
CT scan (industrial CT) to detect internal defects:
- Resolution: 1 μm (detects ≥ 10 μm pores)
- Meets ASTM E407 metallographic inspection standard
- Case Study: Pratt & Whitney GTF Engine Blades Cause Early Fatigue Due to Non-Fusion Defects (NTSB Report)
2. Anisotropy of material properties
The strength in the Z direction may be 15-30% lower than in the XY direction
Solution:
- Heat treatment (HIP hot isostatic pressing) relieves internal stress
- Optimization with scanning strategies (e.g., island scanning)
3. Airworthiness certification challenges
FAA AC 33.15-1 requires that 3D prints must:
- Proof of batch consistency (0.5% deviation in powder chemistry per furnace ≤)
- Perform CT ultrasound dual detection (Airbus Standard NSA 307112-AM)
Current status of 3D printing applications by global aviation giants
| Company | Technology | Application cases | Certification standards |
|---|---|---|---|
| GE Aviation | Electron beam melting (EBM) | LEAP engine nozzle | FAA EASA dual certification |
| Boeing | Selective laser melting (SLM) | 787 titanium alloy bracket | AMS4999A |
| Airbus | Electric arc additive manufacturing (WAAM) | A350 door hinge | EN 9100 supplement |
| Safran | Binder jetting | Auxiliary power unit (APU) housing | ISO/ASTM 52900 |
Conclusion
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Disclaimer
The content appearing on this webpage is for informational purposes only. LS makes no representation or warranty of any kind, be it expressed or implied, as to the accuracy, completeness, or validity of the information. Any performance parameters, geometric tolerances, specific design features, quality and types of materials, or processes should not be inferred to represent what will be delivered by third-party suppliers or manufacturers through LS’s network. Buyers seeking quotes for parts are responsible for defining the specific requirements for those parts. Please contact to our for more information.
Team LS
This article was written by various LS contributors. LS is a leading resource on manufacturing with CNC machining, sheet metal fabrication, 3D printing, injection molding,metal stamping and more.
