Main Landing Gear Research Articles

Comparative Research on Landing and Rollout Characteristics of Skid-Equipped and Wheeled Aircraft

Skid landing gear is a specialized landing device known for its compact structure and lightweight. However, current research on the dynamic characteristics of skid-equipped aircraft on concrete runways is limited, which raises uncertainties about its practical applications. To address this gap, a general aircraft model based on a modular concept is first constructed, considering the coupling effects of aerodynamic, buffer, and ground forces. On this basis, the differences in motion characteristics between skid-equipped and wheeled aircraft are compared in detail. Then, the impact of various factors on the landing characteristics of skid-equipped aircraft is analyzed, such as initial longitudinal velocity, pitching angle, and friction coefficient of skid. Simulation results show that the lack of buffering capability provided by tires results in a 10.57% increase in overload for skid-equipped aircraft and a 15.39% decrease in the efficiency of the main landing gear buffer. Notably, the initial pitching angle has a critical impact on the landing overload of skid-equipped aircraft. Due to the significant differences in the mechanical properties of the landing gears, the skid-equipped aircraft without nose wheel steering ability is a statically unstable system during the rollout phase. The intervention of asymmetric disturbances would pose a serious threat to the rollout safety.

Impact of operator characteristics on landing gear ground manoeuvre occurrences

Abstract The variability in ground manoeuvre occurrences for aircraft landing gear is intrinsically linked to the airport geometries served by aircraft in-service and consequently, the cyclic loads that landing gear carry are driven by the route network and characteristics of aircraft operators. Currently, assumptions must be made when deriving fatigue load spectra for aircraft landing gear, which may fail to capture the operator characteristics, potentially leading to design conservatism. This paper presents the enhanced characterisation of ground turning manoeuvres within the Automatic Dependent Surveillance-Broadcast (ADS-B) trajectories for six narrow-body aircraft across a full-service carrier (FSC) and a low-cost carrier (LCC) fleet. The methodology presented within this paper employs ADS-B latitude and longitude information to overcome limitations of previous approaches, increasing the rate of correct manoeuvre identification within ADS-B trajectories to 77% of flights from the 50% rate achieved previously. When characterising the ground manoeuvres across 3,000 flights, significant differences in manoeuvre occurrences were observed between individual aircraft within the LCC fleet and between the FSC and LCC fleets. The occurrence of tight and pivot turns were shown to vary across the six aircraft with six and eight fatigue-critical turns being performed by the FSC and LCC fleet for every 10 flights performed. In addition, it was observed that the direction of fatigue critical turns is biased in specific directions, suggesting that individual main landing gear assemblies will accumulate fatigue damage at an increased rate, leading to greater justification for operator-specific spectra and structural health monitoring of aircraft landing gear.

Automated packing and piping in an Airbus A320 main landing gear bay: an industrial development case study

The packing of given hydraulic equipment together with the hydraulic piping is a challenging design task. Both the hydraulic domain and the geometry domain are highly intercoupled as the packing determines the exact location of the connection points and tangents for the pipes but also defines the installation spaces for the equipment to be positioned which needs to be taken into account as an obstacle during the piping process. For the industrial case study, a mounting rack in an Airbus A320 main landing gear bay is used, where seven pieces of equipment should be packed and 22 pipes should be routed. In the first part of the study, the packing was done manually, assisted by automated routing, while the hydraulic piping was generated automatically. In the second part of the study the packing was automatized as well. For the automated packing process, a particle multi swarm optimisation was used. As objective function a pipe length minimization was implemented, which uses the Dubins Path as a pipe approximation. Constraints taken into account are the collision-free nature of the equipment and its placement on a plate inside the plates borders. The automated packing workflow was used to generate different variants of which for two a pipe work was generated exemplarily. Due to the model-based systems engineering approach, no further interaction in terms of the definition of the connection points, tangents and the installation space is necessary. This demonstrates that an automated packing and piping process in an industrial context using industrial geometries is now feasible.

Automated pipe design in 3D using a multi-objective toolchain for efficient decision-making

Abstract Pipe design in 3D is typically characterized by competing objectives, since the different design objectives, such as the reduction of length, weight, number of bends, manufacturing cost, and overall angle sum, are examples for such competing design goals, where one goal is often at the expense of the other. The origin of these competing design goals lies in the highly coupled problems of finding a permissible and collision-free pipe path in a complex 3D geometry and the physical properties of the path found. Because of the complex physics and geometry, these couplings are highly non-linear and mostly accessible via simulation only. The underlying pipe design optimization problem can thus not be solved explicitly and is tackled instead with a multi-disciplinary search procedure. Since the trade-offs between different competing evaluation objectives are often not known in advance, an automated design space exploration can be performed to generate different pipe designs, leading to well-informed design decisions by human experts. Such a design space exploration is shown and discussed using the pipework in a mounting rack in an Airbus A320 main landing gear bay. A total of 144 valid designs are generated, out of which the best in each criteria and the pareto-optimal solutions are automatically selected. Compared to the manually created Airbus A320 series solution, up to $10.4\%$ of the pipe length or up to $16.9\%$ of the bends can be saved using the same fixings and connection points, demonstrating both the feasibility and the industrial applicability of the automated toolchain.

Analysis of the Synchronized Locking Dynamic Characteristics of a Dual-Sidestay Main Landing Gear Retraction Mechanism

As an advanced design technology for large wide-body airliners, the three-dimensional (3D) dual-sidestay (DSS) landing gear retraction mechanism can share the ground loads transferred by the landing gear, reducing the load on the wings. However, the addition of a strut system may significantly impact the synchronous locking performance of the landing gear with extremely high sensitivity. To study this impact pattern, both a rigid–flexible-coupling dynamic model of DSS landing gear considering joint clearance and node deviation and a synchronous locking test platform are established in this paper, and the simulation model is validated through the experimental results. Based on the simulation model, this paper conducts a detailed study on the influence of different node deviations and joint clearance on the synchronous locking dynamic characteristics of the DSS landing gear. The results show that, as the node deviation increases, the locking of the lock link gradually lags until one side cannot be fully locked; the structural clearance has a smaller impact on the synchronous locking of the landing gear. The feasible region of parameters satisfying the synchronous locking condition is given, which provides a basis and support for the parameter design of dual-sidestay retraction mechanisms.

Design, structure analysis and shock control of aircraft landing gear system with MR damper

This study proposes a new magneto-rheological aircraft main landing gear (MRAMLG) system and comprehensively treats from a mathematical modelling to drop testing for the evaluation of the landing efficiency. A mathematical model is formulated based on specifications and requirements of existing small aircraft Oleo type landing gear system. To ensure structural stability of the landing gear components such as main trust, column and trunnion, a transient structural analysis is carried out using the finite element method (FEM) and a fatigue life is analysed based on empirical formulas and the rainflow-counting (RC) algorithm. Subsequently, a novel controller is formulated to enhance the landing efficiency by integrating the time delay model and 3-stage hysteresis regulator. In the synthesis of the controller, a desired force model based on the energy law is added to accurately track the desired yield stress needed for the desired field-dependent force. In this work, the proposed control algorithm is named as the model-based force-tracking (MBFT) controller. To evaluate the landing efficiency or shock struct efficiency (SSE) of the proposed MRAMLG, an experimental apparatus for drop test is designed and manufactured by considering a dummy (sprung) mass of 640–720 kg at the maximum sink speed of 3 m s−1. The sink speed represents the rate of descent of the MRAMLG’s tire just before it touches the ground. It is demonstrated from simulation and experiment that the SSE with the MBFT controller is higher than 83% across various landing conditions with different sprung mass and sink speed, while the conventional controllers, proportional-integral and skyhook, compared to MBFT, do not show consistent performance depending on the sprung mass and sink speed.

Vibration Response Analysis of a Main Landing Gear System for High In-Flight Dynamic Loadings

The prediction of aircraft vibrations is necessary for identifying possible design optimization points of each on-board system. In this context, the authors investigated the dynamic response of a Main Landing Gear (MLG) conceived for a fast helicopter when exposed to flight vibrations arisen from the engine propellers. The research activity falls within the Racer program of Clean Sky 2 framework, which aims to develop a novel high-speed rotorcraft. Relying on Airbus Helicopters operative requirements, this paper deals with the numerical procedure description of the MLG dynamic response assessment (resonance frequencies, accelerations amplitude, generalized masses) with respect to the expected in-flight vibrations levels. In particular, an equivalent combined load (sine and random spectrum) based on the normal modes and the corresponding modal mass distribution is employed for investigating the relevant effects on structural endurance. The central themes focus on the possible numerical modelling strategies and vibration loads analysis, which led safely to the qualification. This method could allow for performing sensitivity dynamic analyses in case of further design stiffness or weight changes.

Experimental Structural Validation of a Landing Gear System for High-Speed Helicopter Applications

The design and technological demonstration of a Landing Gear architecture were addressed for Airbus fast rotorcraft end application within the Clean Sky 2 Racer project. Numerical activities including advanced modelling approaches were carried out to substantiate the feasibility of structural concepts in compliance with industrial standards and CS-29 applicable airworthiness requirements. In order to demonstrate the goodness of design strategies, a true-scale prototype was manufactured and tested for demonstrating its capability to withstand static loads representative of the limit and ultimate cases expected in service. The paper will focus on the qualification of the Nose and Main Landing Gear systems. Sizing process was validated and verified by test whose results allowed for validating/calibrating the FE model. In such a way, the design database could count on a reliable tool available for analysing the effect of any further load condition change.

Development of Novel Wear Equation of AA7050/SiC-Steel Interface for High Temperature Application

AA7050 aluminium alloy used for the main landing gear link was reinforced with SiC particles utilizing stir casting and uniform dispersion of reinforced particles was analyzed through SEM with EDS mapping. Wear test were performed on pin on disc apparatus by varying the process parameters and experimental runs were designed using response surface methodology. The influence of SiC particles on wear resistance at high temperatures was explored and the findings led to the development of a novel wear equation. The hardness of composites increased due to impediments of dislocation movement, and it declines with an increase in temperature owing to a reduction of Pierls stresses. The formation of a Mechanically Mixed Layer (MML) enhances wear resistance with the inclusion of reinforced particles, and the breakdown of this layer swifts the wear from moderate to severe. The mode of wear was a combination of shearing and abrasive at room temperature, shearing and adhesive until the temperature 200ᵒC, and plastic deformation when the temperature exceeded 200 °C, which was confirmed by worn surface morphology.

Vibration Qualification Campaign on Main Landing Gear System for High-Speed Compound Helicopter

Vibrations in helicopters have strong implications for their performance and safety, leading to the increased fatigue of components and reduced operational efficiency. As helicopters are designed to land on several types of surfaces, the landing gear system dissipates the impact on the ground and maintains stability during landing and take-off. These vibrations can arise from a variety of sources, such as aerodynamic loads, mechanical imbalances, and engine instabilities. In the present work, the authors describe the vibration qualification process of the main landing gear tailored to fast helicopters within the Clean Sky 2 Racer program. The method entails devising preliminary load sets that deform the structure in its key excited mode shapes to assess stresses and address the experimental campaign. A full-scale prototype model is then tested for sine sweep and random vibrations as per the Airbus Helicopter requirements in order to reach the final qualification and acceptance stage. Although the discussion centers on a landing gear structure, the described process could be extended to other critical equipment as well.

A probabilistic approach for acoustic emission based monitoring techniques: With application to structural health monitoring

It has been demonstrated that acoustic-emission (AE), inspection of structures can offer advantages over other types of monitoring techniques in the detection of damage; namely, an increased sensitivity to damage, as well as an ability to localise its source. There are, however, numerous challenges associated with the analysis of AE data. One issue is the high sampling frequencies required to capture AE activity. In just a few seconds, a recording can generate very high volumes of data, of which a significant portion may be of little interest for analysis. Identifying the individual AE events in a recorded time-series is therefore a necessary procedure for reducing the size of the dataset and projecting out the influence of background noise from the signal. In this paper, a state-of-the-art technique is presented that can automatically identify cluster the AE events from a probabilistic perspective. A nonparametric Bayesian approach, based on the Dirichlet process (DP), is employed to overcome some of the challenges associated with this task. Additionally, the developed model is applied for damage detection using AE data collected from an experimental setup. Two main sets of AE data are considered in this work: (1) from a journal bearing in operation, and (2) from an Airbus A320 main landing gear subjected to fatigue testing.

Application of Topology Optimization Method for Unmanned Aerial Vehicle Nose Landing Gear Fork

İniş takımı uçağın en önemli bileşenlerinden biridir. Uçağa gelen yükleri karşılamak, iniş anında darbeyi sönümlemek ve uçağın taksi yapmasına izin vermek iniş takımının görevleri arasındadır. İniş takımı, ana iniş takımı ve burun iniş takımından oluşur. Ana iniş takımı ve burun iniş takımı da kendi içinde alt bileşenlerden oluşur. Bu çalışmada burun iniş takımı alt bileşenlerinden olan çatal parçası için optimizasyon çalışması yapılmıştır. Optimizasyonun amacı, performansı ve tasarımı iyileştirmek, hafifletmek, talaş miktarını ve proses enerjisini azaltmaktır. Çatal parçasının optimizasyon çalışması için gerekli sınır koşulları verilerek, analiz ANSYS Workbench programında gerçekleştirilmiştir. Optimizasyondan sonra, analiz çalışmasında oluşan gerilme ve deformasyonlar optimizasyon öncesi sonuçlarla karşılaştırılarak çatal yapısı doğrulanmış ve yapısal değişiklikler oluşturularak ağırlık azaltılmıştır.

Toward Airframe Noise Reduction for Passenger Aircraft

Airframe noise is one of the main noise sources of the latest passenger aircraft during the approach phase. To demonstrate noise reduction technology based on unsteady Computational Fluid Dynamics (CFD) and wind tunnel tests, JAXA conducted flight tests using the JAXA Experimental Aircraft "Hisho" in 2016 and 2017 in cooperation with industries in Japan. The noise data obtained from flyover noise source measurements successfully showed consistent characteristics with the noise reduction designs for the flaps and the main landing gear. The noise measurement data from the flight test 2017 were used to validate the wind tunnel tests and CFD used in the design phase. Subsequently, the research activities proceeded towards the research and development targeting regional jet aircraft, aiming for practical application in passenger aircraft. This paper overviews these research activities toward developing airframe noise reduction technology for passenger aircraft.

Predicting the Remaining Useful Life of Light Aircraft Structural Parts: An Expert System Approach

This paper introduces an expert system approach for predicting the remaining useful life (RUL) of light aircraft structural components by analyzing operational and maintenance records. The expert system consists of four modules: knowledge acquisition, knowledge base, inference, and explanation. The knowledge acquisition module retrieves data from mandatory records, such as aircraft logbooks and mass and balance sheets. The knowledge base stores specific remaining useful lives (SRULs) for different load profiles that are determined using numerical strength analysis. The inference module utilizes the Palmgren-Miner rule to estimate the accumulated fatigue damage of the structural component based on the input data and the knowledge base. Lastly, the explanation module links the accumulated damage to the maintenance program and suggests the appropriate maintenance action. The Cessna 172R main landing gear leg is utilized as a case study, demonstrating the variance of RUL depending on the operating conditions. The objective of this approach is to enhance light aircraft maintenance decision making and advance operational safety.

Design optimisation and experimental verification of a UAV’s landing gear buffer

The landing gear is a critical aircraft system that absorbs the kinetic energy of the vertical load and reduces the aircraft’s impact at touchdown. This paper proposes a hybrid optimisation method for further optimising the buffer performance of a mature UAV’s main landing gear. This method combines a propagation (BP) neural network method with a genetic algorithm (GA). A landing gear dynamics simulation model is established based on the software LMS Virtual.Lab Motion, and validate the model with tests. The optimisation model is established using a BP neural network and solved using a genetic algorithm. The maximum vertical load, the efficiency coefficient of buffer, and the efficiency coefficient of buffer system are used as the optimisation targets. The air chamber initial gas pressure, initial volume of buffer, and diameter of main oil hole are selected as the optimisation parameters, and the values after optimisation are 148 MPa, 165.2 mL, and 3.17 mm, respectively. The results show that the efficiency coefficient of buffer is increased by 3.7% and the efficiency coefficient of buffer system is increased by 1.13% and the maximum vertical load decreased by 0.6%, which indicated that the hybrid optimisation method is effective for landing gear buffering performance.

Linear and Nonlinear Models for Drop Simulation of an Aircraft Landing Gear System with MR Dampers

In this study, our focus is on the drop test simulation of an MR (Magnetorheological) damper-based main landing gear (MRMLG), aiming to explore multi-degree-of-freedom (DOF) dynamic models during aircraft landing. Three different 6-DOF dynamic models are proposed in this work, and their drop performances are compared with results achieved by commercial software. The proposed models include a nonlinear aircraft model (NLAM); a linearized approximated aircraft model (LAAM) linearizing from the nonlinear equations of motion in NLAM; and a fully approximated aircraft model (FAAM) which linearizes the MRMLG’s strut force model. In order to evaluate the drop performance of the aircraft landing gear system with MR dampers, a 7-DOF aircraft model incorporating the nonlinear MRMLG was formulated using RecurDyn. The principal comparative parameters are the coefficient of determination (R2) for the system response of each model with the RecurDyn model and root mean square error (RMSE), which is the ensemble of CG displacement data for each model. In addition, the ensemble of time series data is created for diverse drop scenarios, providing valuable insights into the performance of the proposed drop test models of an aircraft landing gear system featuring MR dampers.

Evaluation of aircraft random vibration under roughness excitation during taxiing

The assessment of runway smoothness or roughness is intimately tied to the vibrational response of aircraft during taxiing. In this study, employing the pseudo excitation method (PEM) based on random vibration analysis, we unearthed the relationship between the random vibrations of five distinct aircraft types and runway irregularities. Initially, we established two three-dimensional (3D) models of aircraft taxiing vibration and derived the response output under roughness excitation. Subsequently, we employed MATLAB to analyze the power spectral characteristics of the vibrational response in different parts of the aircraft. Lastly, we examined the effects of taxiing speed, aircraft type, runway roughness, and lift on the aircraft's vibration. Our findings indicate that the distribution of vibration power spectral density (PSD) exhibits multiple peaks, correlating with the degrees of freedom of the aircraft. We further note that the frequency that aligns most closely with the response peak should be the focus of investigation. High-frequency excitation impacts the pilot and nose landing gear more significantly than the passenger and main landing gear. Absent the consideration of lift, increased taxiing speed amplifies the impact of roughness excitation on aircraft taxiing safety. Larger aircrafts are more sensitive to long-wave roughness. With lift in consideration, all aircraft types exhibit a speed sensitivity to vibration, which should be the primary concern in runway roughness evaluations.

Structural Optimization of the Lower Door of the Main Landing Gear of an Aircraft

In this paper, the topology optimization algorithm is used to optimize the main structure of the main landing gear lower door of an aircraft by combining the structural strength, structural stiffness, and processing technology [1-2]. Considering the balance of structural weight, structural strength, and material distribution, the structural topology optimization design result with reasonable structure, good manufacturability, and moderate weight is finally obtained.

Vibration Response Law of Aircraft Taxiing under Random Roughness Excitation

Understanding the vibration response patterns of aircraft taxiing under runway roughness excitation is crucial for aircraft design and runway performance evaluation. In this paper, we establish pavement roughness models for both asphalt and concrete surfaces, taking into account their unique structural characteristics. We construct a six-degrees-of-freedom aircraft model using multi-rigid-body system dynamics theory and employ the pseudo-excitation method to examine the influence of pavement roughness types on the steady vibration response of aircraft taxiing at constant speeds. Furthermore, we analyze the non-stationary vibration response patterns of aircraft during takeoff and landing taxiing using the method of instantaneous frequency response function with space frequency. Lastly, we explore the effect of stochastic structural parameters on aircraft vibration response using the Monte Carlo method. Our findings reveal that the roughness power spectrum differs between asphalt and concrete pavements, and the established roughness models in this paper demonstrate a strong fit (R2 > 0.95). The type of pavement roughness has a relatively minor impact on the power spectral density distribution of the aircraft vibration response, suggesting that the same roughness model can be used for both asphalt and concrete pavements when high accuracy is not required. The power spectral density distribution of aircraft vibration response varies across different motion attitudes, with the vibration response during landing being significantly larger than that during takeoff. Among the aircraft structural parameters, the randomness of the sprung mass has the most substantial effect on the aircraft vibration response, potentially causing the variation coefficient of dynamic load on the front landing gear to exceed 0.11. Tire stiffness comes next, which can lead to the variation coefficient of dynamic load on the main landing gear reaching 0.07. The results have a guiding role in optimizing aircraft structure design and ensuring pavement performance.

Characterization of Slat Noise Radiation from a High-Lift Common Research Model

A test campaign was conducted in the open-jet test section of the NASA Langley Research Center’s 14- by 22-Foot Subsonic Tunnel on a 10%-scale semispan version of the High-Lift Common Research Model incorporating a leading-edge slat, a trailing-edge flap, and removable high-fidelity main landing gear. Computational simulations were used to support the model development, provide important information such as load distributions along the high-lift elements, and aid in the design of noise reduction devices. Aerodynamic and far-field acoustic measurements were obtained on baseline and acoustically treated model configurations using an ensemble of time-averaged and unsteady surface pressure sensors paired with a traversing 97-microphone phased array viewing the pressure side of the airframe. A deconvolution method incorporating corrections for shear layer acoustic wave decorrelation was employed to determine the locations and strengths of relevant noise sources along the span of the slat and in the vicinity of the flap edges and landing gear. The main goal of the test campaign was to use the surface pressure and array data to evaluate the effectiveness of various slat noise reduction concepts. It was found that slat-gap fillers produced significant broadband noise reduction with minimal aerodynamic performance penalties for all Mach numbers and airfoil angles of attack that were investigated. The test campaign clearly demonstrated the noise reduction benefits that can be obtained by applying appropriate treatments to leading-edge slats on commercial transport-class aircraft.