Torque Link Research Articles

On the mitigation of landing gear noise using a solid fairing and a dense wire mesh

A solid fairing and a wire-mesh fairing consisting of very fine wires and pores are numerically and experimentally investigated for the mitigation of landing gear noise. A slightly modified LAGOON landing gear and two configurations, one equipped with a solid fairing and the other with a wire-mesh fairing, are numerically simulated using the Improved Delayed Detached-Eddy Simulation (IDDES) in combination with the Ffowcs Williams and Hawkings (FW-H) analogy. Instead of resolving the detailed flow features through the wire mesh, a recently proposed numerical model is used to represent the effect of the wire-mesh fairing. The simulated flow fields and the far-field noise spectra are validated against the experiments conducted in an anechoic wind tunnel. The superiority of the recently proposed wire-mesh model over a classical wire-mesh model in modelling both the aerodynamic and aeroacoustic effects of the wire mesh is demonstrated. Results also show that the dense wire-mesh fairing functions very similarly to the solid fairing and that significant noise can be reduced through the installation of a solid fairing or a wire-mesh fairing upstream of the landing gears. For the baseline landing gear, the torque link and the brakes are identified noise sources. With the aerodynamic penalty of a 50% increase in drag, both fairings mitigate the pressure fluctuation on the torque link and brakes, resulting in the reduction of surface noise sources. The noise directivity shows that a solid fairing or a dense wire-mesh fairing contributes to a noise reduction of 4-6 dB in all radial directions. The findings in this study pave the way for the low-noise design of aircraft landing gears.

Structural Design Analysis Torque Links of Nose Landing Gear on Light Aircraft

Torque links are components of Nose Landing Gear on the designed lightweight aircraft, that connect between the inner and outer cylinders of an oleo-pneumatic shock strut. They prevent torsion or twisting between those components and vibrations at retractable nose landing gear, the safety of these components is very important, especially when landing aircraft. This paper studies the stress and deformation contours of the torque link design with variations of hole geometry to get the optimal design, with the lightest possible weight but still reliable and safe. The upper torque link is modeled as a simply supported beam with a moment on one end derived from impact force when landing. Maximum bending stresses occur in areas near holes and the connection part of the torque link. This analysis with a tetra mesh by changing the hole position and geometry. The final torque link design results in a weight reduction of up to 23.75% with a maximum stress is 157.4 MPa and displacement is 0.0166 mm. Torque link design optimization results are then modally analyzed, and four natural frequencies and the mode shape are done. The natural frequency of vibration of different mode shapes obtained ranges from 4.2259 kHz to 6.1319 kHz, and this is still below the limit of 0.1 kHz (around 6,000 rpm engine). Finally, the optimal design torque links were obtained, safe from static and dynamic loads with a Factor of Safety 1.78 (>1.5) according to the FAR-23 standard.

Effect of clearance position of torque link structure on nose landing gear shimmy

The clearance of the torque link will affect the stability of landing gear shimmy. In this paper, a six-degree-of-freedom mathematical model of dual-wheel nose landing gear shimmy including longitudinal bending and axial displacement of the strut is established. The shimmy characteristics of five different positions of clearance at the central connecting pin of the lower torque link and connection between the lower torque link and the inner cylinder of the strut are analyzed by bifurcation diagram, limit cycle and time history diagram. The results show that: there is a clearance on both sides of the head of the lower torque link, compared with the clearance exists only on one side (left or right), the range of the torsional shimmy of the nose landing gear is larger; when there is a clearance on one side (left or right) near 2 mm at the connection between the lower torque link and the inner cylinder of the strut, the torsional shimmy appears a period doubling phenomenon.

Fatigue life prediction of topologically optimized torque link adjusted for additive manufacturing

The torque link is part of the nose landing gear of aircraft. It prevents the piston from turning inside the cylinder of the shock absorber, enabling its up and down motion during the landing and take-off. As such, its structural integrity and life are crucial for aircraft safe operation, but because of complex geometry and variable loading conditions, its fatigue life estimation represents a real challenge. In this paper, fatigue lives of two different designs of the torque links of the light aircraft are evaluated by a numerical approach based on the improved FEM. Firstly, the fatigue life of the damaged torque link was assessed for actual load conditions. Then, improved torque links, obtained through topological optimization, were analyzed and their fatigue life was calculated. Finally, the numerical simulations of the additive manufacturing (AM) process of optimized torque links were carried out, and the fatigue life of these torque links, including residual stresses from AM, were estimated too. The obtained numbers of cycles in all cases were compared and discussed for all torque links cases. This is an advanced approach to fatigue life assessment of optimized printed 3D parts based on numerical simulations of both crack growth and AM process.

Evaluation of Joint Clearance Effects on the Shimmy of Nose Landing Gear

Through the establishment of a three-dimensional joint clearance model, the effects of joint clearances at different positions on shimmy stability are evaluated. In this paper, considering the radial, axial and coupling characteristics of joint clearance, the shimmy multibody dynamics (MBD) model is applied to different joints in the nose landing gear (NLG) transmission system. It is proposed to evaluate the influence of joint clearance on shimmy from two aspects of position factor and wear factor. The study found that different joint clearances have different effects on shimmy: the joint clearance between the NLG and fuselage has little influence on shimmy; the larger axial clearance of upper and lower torque link joint will cause the shimmy of the NLG, but the radial clearance has no effect on shimmy; while the joint clearance between turning sleeve and upper torque link, lower torque link and piston only works in the axial and radial coupling. The reasons for the different influence characteristics of each joint space are analyzed. Consequently, studying and summarizing the influence of different clearance on shimmy is of great significance for the design and maintenance of the NLG joints.

A Numerical Study of the Wind Speed Effect on the Flow and Acoustic Characteristics of the Minor Cavity Structures in a Two-Wheel Landing Gear

The landing gear is widely concerned as the main noise source of airframe noise. The flow characteristics and aerodynamic noise characteristics of the landing gear were numerically simulated based on Large Eddy Simulation and Linearized Euler Equation, and the feasibility of the simulation model was verified by experiments. Then the wind speed effect on the flow and acoustic characteristics of the minor cavity structures in a two-wheel landing gear were analyzed. The results show that the interaction of vortices increases with the increase of velocity at the brake disc, resulting in a slight increase in the amplitude of pressure fluctuation at 55 m·s−1~75 m·s−1. With the increase of speed, the obstruction at the lower hole of torque link decreases, and many vortical structures flow out of the lower hole and are dissipated, so that the pressure fluctuation amplitude of 75 m·s−1 almost does not increase relative to 55 m·s−1. The contribution of each part in the landing gear to the overall noise is as follows: shock strut > tire > torque link > brake disc. At the speed of 34 m·s−1~55 m·s−1, the contribution of each component to the total noise increases with the increase of speed, and the small components such as torque link and brake disc contribute more to the total noise. At the speed of 55 m·s−1~75 m·s−1, the increase of overall noise mainly comes from the main components such as shock strut and tire, and the brake disc and torque link contribute very little to the overall noise. It provides a reference for the further noise reduction optimization design of the landing gear.

Experimental study of realistic low–noise technologies applied to a full–scale nose landing gear

The landing gear system is the dominant airframe noise source for most modern commercial aircraft during approach. This manuscript reports the results from the ALLEGRA (Advanced Low Noise Landing (Main and Nose) Gear for Regional Aircraft) project. This project assessed the performance of several highly realistic low–noise technologies (LNTs) applied to a detailed full–scale nose landing gear (NLG) model in aeroacoustic wind–tunnel experiments. Four individual low–noise concepts tested, namely a ramp door spoiler, a solid wheel axle fairing, wheel hub caps, and multiple perforated fairings. Combinations and small variations of some of these LNTs were also evaluated. The use of multiple planar microphone arrays allowed for the application of 2D and 3D acoustic imaging algorithms to assess the location and strength of the noise sources within the NLG system in different emission directions for each configuration. The wheel axle, the inner wheel hubs, the steering pinions and the torque link were identified as the noisiest NLG elements. The solid wheel axle fairing was the most effective individual LNT, and it improved its performance when applied in combination with the ramp door spoiler and wheel hub caps, reaching overall noise reductions of more than 4 dBA.

Experimental characterization of a novel nose landing gear shimmy damper using a small-scale test rig

This paper presents the design and fabrication details of a small-scale testing system for characterizing a novel nose landing gear shimmy damper. This test rig is designed to simulate take-off and landing conditions of an aircraft nose landing gear in the laboratory environment. A roller drum is employed to simulate the forward speed of the aircraft on the ground, while an impact hammer mechanism is used to induce shimmy through a small initial tire slip. Weights can be used to induce vertical force exerted by the fuselage. The vibration signals are recorded using accelerometers, and processed numerically to obtain shimmy characteristics. A prototype of the novel shimmy damper designated as the Symmetric Torque Link Damper (STLD) is fabricated. The specifications of STLD are discussed in previous publications and summarized in the current paper. The experimental results including rotational vibration time histories, peak frequencies, and attenuation characteristics for the STLD are presented and compared with those of the baseline system without a shimmy damper, as well as with the built-in shimmy damper trends. Overall, this experimental work confirms the stability gain offered by the STLD, while it does not outperform the built-in damper in all scenarios. Instead, STLD has the attractive features of being retrofittable to existing landing gears and is symmetric in design, leading to an even distribution of dynamics loads on the gear. Furthermore, the testing apparatus presented in this work contributes to shimmy mitigation practice by offering a novel, yet simple, validation approach suitable for early prototype developments.

Structural design and optimization of a novel shimmy damper for nose landing gears

Passive vibration suppression devices known as shimmy dampers are vital in maintaining stability and safety of certain landing gears. Yet, systematic design, performance analysis, and optimization of such devices are rarely discussed in the literature. This paper presents structural design optimization of a novel shimmy damper for nose landing gears. This new design is a multifunctional mechanism integrating the shimmy damper into the torque link system of the nose landing gear. It features symmetric load distribution, and it can be tailored to existing nose landing gears. Here, the damper design concept is developed in the structural sense and optimized for the nose landing gear of a Piper Cheyenne aircraft. Dynamic loads from a representative shimmy scenario are employed in the analysis and design procedures. Utilizing equivalent static load method, topology optimization with transient loads is performed to obtain optimal material distribution satisfying the objective function and constraints. Flexible multibody dynamics analysis based on a high-fidelity finite element model is utilized in the analysis of design candidates and for validating the final design. To ensure adequate strength under the dynamic torque loads and to offer sufficient damping needed for stabilizing the nose landing gear, a three-piece torque link mechanism emerged through multiple design iterations guided by the topology optimization. Using numerical simulations, the final design is shown to satisfy the strength requirement while providing sufficient damper stroke. The results from the present study signal a vast potential in improving shimmy mitigation strategies by eliminating the need for costly redesigns of landing gears susceptible to shimmy.

Interaction of torque link freeplay and Coulomb friction nonlinearities in nose landing gear shimmy scenarios

Aircraft nose landing gears are known to be prone to shimmy oscillations, rooted mainly in inadequate design and maintenance. Being a highly nonlinear dynamical system, stable limit-cycles can arise for certain values of input parameters, which are both a nuisance to the occupants and a threat to the safety and integrity of the aircraft. Influence of different landing gear nonlinearities are discussed in differing depth in the literature, leaving the interaction and simultaneous effect of these nonlinearities mostly unexplored. In particular, Coulomb friction in the shock absorber is largely neglected or oversimplified, while it was shown in the authors’ previous work to have a substantial effect on the stability boundaries. In the present novel investigation, we further explore the significance of state-dependent Coulomb friction in the shock absorber in presence of rotational freeplay, which is another key nonlinearity of the landing gear systems. Using a representative high-fidelity Multi-Body Dynamic model and numerical solution scheme in the time domain, 3D shimmy maps and 2D stability boundaries are obtained and employed to understand the nonlinear phenomena of interest, contributing to more realistic performance estimation of nose landing gears in early design stages. Together with time histories of the limit-cycles, phase portraits, and frequency spectra for selected inputs, the stability maps showed that presence of freeplay leads to emergence of a new area in the stability map, characterized with low-amplitude rotational oscillations and zero steady-state lateral amplitude. Furthermore, with Coulomb friction and freeplay both being part of the model, the freeplay-induced area of the stability map vanishes, while the freeplay effect is still manifested in the frequency spectra and expansion of the rotational-dominant area. The sensitivity of the freeplay-induced changes to the magnitude of the torque link freeplay is also depicted and discussed, for cases with and without Coulomb friction.

Parametric study of a novel nose landing gear shimmy damper concept

Shimmy dampers are passive solutions for undesired shimmy vibration in aircraft landing gears. Although they mitigate shimmy to variable degrees, they can introduce weight, cost, and reliability penalties especially when added to existing landing gear systems. More effective and compact shimmy dampers with reduced maintenance effort and enhanced stability performance can then greatly contribute to light-weighting, as well as lowering the aviation risk and maintenance costs. Moreover, a robust performance analysis and characterization framework based on high-fidelity computational models is absent from the literature while it is essential to quantify the capabilities of a given damper. In this work, analysis of a novel shimmy damper concept is presented along with an effective methodology for evaluating the performance of shimmy dampers based on nonlinear shimmy amplitude maps and stability boundary plots. The new damper concept is suitable for installation on existing and new landing gears and features a multifunctional torque link member including an assembly of beam and damping units to suppress the undesired vibrations. The influence of torque link damper parameters is then thoroughly explored using the nonlinear Multibody Dynamics model of the nose landing gear employed for both generating the shimmy maps and time histories of the vibrations. The novel concept is shown to be capable of effectively mitigating the rotational shimmy given that the parameters are chosen appropriately based on the systematic approach laid out. The insights from the analysis are then distilled in the form of recommendation for designing next generation shimmy dampers. Moreover, the novel framework introduced for characterizing shimmy dampers offers great benefit to the shimmy suppression research and development practice.

Impacts of rice husk ash filler loading on curing, morphological characteristics and tensile properties of natural rubber/ethylene propylene rubber blends

Rice husk is an agro industrial waste that potentially used in biomaterial application. It contains high silica that could be utilized as a reinforcing filler to substitute commercially precipitated silica or other commercial fillers in rubber compounding application. This research studied the effect of rice husk ash (RHA) loading as reinforcing filler in Natural Rubber/Ethylene Propylene rubber (NR/EPR) blends. The effects were observed by applying 40, 50, 60, 70 phr of RHA filler in the rubber compounding for NR (100) and also for blending NR/EPR (70:30). The rubber compounding and vulcanization for the rubber compounding was conducted according to the ASTM D-3182. The results showed that RHA were successfully prepared and introduced as a new alternative filler for rubber industrial application. Based on the curing characteristics, the RHA loading influence slightly ts2, t90, ML, MH and cross link density on the NR blending with and without EPR addition. At the same RHA composition, the torque and cross link density of NR-EPR blending were much higher compared to only NR. RHA loading on NR with and without EPR composites caused a slight decreasing on tensile strength, elongation at break, and compression set. Conversely, the hardness of those composites tended to increase due to the RHA addition. The SEM micrographs provided additional evidences on the poor tensile properties as well as the matrix tearing and voids due to EPR addition into NR composites. To sum up, RHA may be used as an alternative filler for NR composites along with the EPR addition in order to improve compression set and hardness properties without losing tensile properties of the composites.

Noise Characterization of a Full-Scale Nose Landing Gear

This paper presents experimental results from a nose landing-gear test campaign. A highly detailed model of the nose section of a 90-seat configuration green regional aircraft concept was built and tested in an aeroacoustic open-jet wind tunnel at full scale. All of the landing-gear components, fixtures, and small details and associated structures such as the complete wheel bay, bay doors, and hydraulic dressings were included at full scale. This paper focuses on one element of the testing: that of component noise assessment. The dressings, wheels, torque link, steering pinion, bay doors, and then the main strut and drag stay were removed in succession, and an acoustic evaluation was performed at a range of velocities from to . In addition, hub caps were installed on the wheels, and their performance as a low-noise treatment is presented and assessed for efficacy. The landing gear, doors, and bay generated most noise in the frequency range between 120 and 400 Hz, but appreciable noise above the baseline was measured up to 10 kHz. The low- to midfrequency aerodynamic noise was found to scale with , as usual; however, the spectra at high frequencies collapsed perfectly when scaled to , confirming the fact that high-frequency noise is radiated from the turbulent flow surrounding small features. The total noise output of the landing-gear assembly differs from that of the sum of the components in isolation due to installation effects. The research in this paper studied these effects and the influence of the components on each other.

Prediction of landing gear loads using machine learning techniques

This article investigates the feasibility of using machine learning algorithms to predict the loads experienced by a landing gear during landing. For this purpose, the results on drop test data and flight test data will be examined. This article will focus on the use of Gaussian process regression for the prediction of loads on the components of a landing gear. For the learning task, comprehensive measurement data from drop tests are available. These include measurements of strains at key locations, such as on the side-stay and torque link, as well as acceleration measurements of the drop carriage and the gear itself, measurements of shock absorber travel, tyre closure, shock absorber pressure and wheel speed. Ground-to-tyre loads are also available through measurements made with a drop test ground reaction platform. The aim is to train the Gaussian process to predict load at a particular location from other available measurements, such as accelerations, or measurements of the shock absorber. If models can be successfully trained, then future load patterns may be predicted using only these measurements. The ultimate aim is to produce an accurate model that can predict the load at a number of locations across the landing gear using measurements that are readily available or may be measured more easily than directly measuring strain on the gear itself (for example, these may be measurements already available on the aircraft, or from a small number of sensors attached to the gear). The drop test data models provide a positive feasibility test which is the basis for moving on to the critical task of prediction on flight test data. For this, a wide range of available flight test measurements are considered for potential model inputs (excluding strain measurements themselves), before attempting to refine the model or use a smaller number of measurements for the prediction.

Control simulation of PMSM traction system of high speed train when passing neutral section

Purpose – In electric system of high-speed trains, neutral sections are set to balance the three-phase load. When passing neutral sections, the train should detach from the power supply for a short time. To permanent magnet synchronous motors (PMSMs) traction system, the voltage of DC link will increase quickly due to the back-EMF of PMSM during this time. Although the energy consumption braking method can be adopted to consume the feedback energy. It not only wastes energy, but also causes more speed drop of the train. The paper aims to discuss these issues. Design/methodology/approach – In order to get better performance when the train is under passing neutral section condition, a suitable control method is proposed, in which the torque command is set to zero and d-axis current order remains unchanged during passing neutral section. Based on a co-simulation model, the influences of this method on the PMSMs traction system are compared with that of traditional method, which is used in induction motors traction system. This model combines both control strategy and finite element model of motor, which can take the effects of magnetic saturation and power loss into consideration. Findings – In PMSMs traction system, PMSMs work as generators during neutral section, and charge to DC bus, which may cause over-voltage damage. Moreover, there would be strong torque shock at the moment of power cut-off. It is finally found that, with the suitable control method, the high-speed train can pass the neutral section with less speed drop, less torque shock and little DC link voltage rise. Originality/value – The control method proposed in this paper is easier to achieve and gets a better performance of PMSMs traction system in high-speed train compared with the traditional method. Furthermore, the co-simulation model is much closer to reality than the analytical model.

Effect of noise reducing components on nose landing gear stability for a mid-size aircraft coupled with vortex shedding and freeplay

In the pursuit of quieter aircraft, significant effort has been dedicated to airframe noise identification and reduction. The landing gear is one of the main sources of airframe noise on approach. The addition of noise abatement technologies such as fairings or wheel hub caps is usually considered to be the simplest solution to reduce this noise. After touchdown, noise abatement components can potentially affect the inherently nonlinear and dynamically complex behaviour (shimmy) of landing gear. Moreover, fairings can influence the aerodynamic load on the system and interact with the mechanical freeplay in the torque link. This paper presents a numerical study of nose landing gear stability for a mid-size aircraft with low noise solutions, which are modelled by an increase of the relevant model structural parameters to address a hypothetical effect of additional fairings and wheel hub caps. The study shows that the wheel hub caps are not a threat to stability. A fairing has a destabilising effect due to the increased moment of inertia of the strut and a stabilising effect due to the increased torsional stiffness of the strut. As the torsional stiffness is dependent on the method of attachment, in situations where the fairing increases the torsional inertia with little increase to the torsional stiffness, a net destabilising effect can result. Alternatively, it is possible that for the case that if the fairing were to increase equally both the torsional stiffness and the moment of inertia of the strut, then their effects could be mutually negated. However, it has been found here that for small and simple fairings, typical of current landing gear noise abatement design, their implementation will not affect the dynamics and stability of the system in an operational range (Fz≤ 50000N, V≤ 100m/s). This generalisation is strictly dependent on size and installation methods. The aerodynamic load, which would be influenced by the presence of fairings, was modelled using a simple vortex shedding oscillator acting on the strut. The stability boundary was found to remain unaltered by vortex shedding. Significantly however, the addition of freeplay in the torque link was found to cause shimmy over the more typical operating conditions studied here. Unlike the no-freeplay case, there was a suppressed stabilising effect of increased torsional stiffness of the strut caused by the presence of fairing. No interaction between the vortex shedding and the freeplay on the stability threshold was observed.

Effects of Freeplay on Dynamic Stability of an Aircraft Main Landing Gear

A study is made into the occurrence of shimmy oscillations in a dual-wheel main landing gear. Nonlinear equations of motion are developed for the system, and various effects are considered, including gyroscopic coupling, nonlinear tire properties, geometric nonlinearities, and fluid shock damping. Of particular interest in this study is the presence of freeplay: this is introduced as a lateral play at the apex of the torque link joints. Using bifurcation analysis methods, the dynamics of this system are explored as the forward velocity and loading force acting on the gear are varied. For the zero freeplay case, the system is found to be stable over its physical operating range with shimmy oscillations appearing only for extreme loading forces and speed. However, with the introduction of freeplay, shimmy may be observed over more typical operating conditions, and the resulting oscillations are found to scale linearly with freeplay magnitude. The parameter plane of forward velocity and loading force is then further subdivided into areas of different types of dynamics. With the inclusion of freeplay one observes the appearance of low-frequency and high-frequency shimmy oscillations, bistable behavior, and stationary solutions of nonzero yaw. Considering the desirable case in which no shimmy occurs, the set of allowable freeplay profiles that satisfy a conservative stability criteria is defined.

Landing Gear Aerodynamic Noise Prediction Using Building-Cube Method

Landing gear noise prediction method is developed using Building-Cube Method (BCM). The BCM is a multiblock-structured Cartesian mesh flow solver, which aims to enable practical large-scale computation. The computational domain is composed of assemblage of various sizes of building blocks where small blocks are used to capture flow features in detail. Because of Cartesian-based mesh, easy and fast mesh generation for complicated geometries is achieved. The airframe noise is predicted through the coupling of incompressible Navier-Stokes flow solver and the aeroacoustic analogy-based Curle’s equation. In this paper, Curle’s equation in noncompact form is introduced to predict the acoustic sound from an object in flow. This approach is applied to JAXA Landing gear Evaluation Geometry model to investigate the influence of the detail components to flows and aerodynamic noises. The position of torque link and the wheel cap geometry are changed to discuss the influence. The present method showed good agreement with the preceding experimental result and proved that difference of the complicated components to far field noise was estimated. The result also shows that the torque link position highly affects the flow acceleration at the axle region between two wheels, which causes the change in SPL at observation point.

Bluff body flow-induced noise control with sliding plasma actuators

Sliding plasma actuators were used to control the flow-induced broadband noise radiating from a bluff body. The structure consisted of a cylinder and a torque link that was installed on the lee side of the cylinder. The objective was to reduce the noise generated during the cylinder wake impinging on the torque link. By manipulating cylinder wake with the externally-imposed body force generated by the plasma actuators, the flow-structure interaction was reduced, leading to an attenuation of the broadband noise up to 3 dB in overall sound pressure level at a free stream speed of 30 m/s.

헬리콥터 착륙장치 복합재 토크링크 피로내구성에 대한 실험적 연구

This research work contributes to a study for the procedure and methodology to assess the fatigue durability for a composite torque link for helicopter landing gear, which was newly developed and fabricated by the resin transfer moulding technique to interchange with metal component. The simulated load spectrum anticipated to be applied to the torque link during its operation life was generated using an advanced method of probabilistic random process, and the fatigue durability was evaluated by the residual strength degradation approach on the basis of material test data. The full scale fatigue test was performed and compared with the analysis results.