Landing Gear System Research Articles

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.

MBFHA: A Framework for Model‐Based Functional Hazard Assessment for Aircraft Systems

AbstractTo address growing system complexity in the aerospace industry, a Model‐Based Systems Engineering (MBSE) approach has been increasingly adopted for the development of aircraft systems. This calls for a corresponding approach for performing safety assessment to maintain consistency between the system and safety domains. One of the key safety assessment processes for aircraft development is the Functional Hazard Assessment (FHA). The purpose of this paper is to build upon previously published works and introduce the MBFHA framework which describes the language, method, and tool needed for implementing a model‐based approach to performing FHA and integrating it into MBSE activities. A customised FHA profile is introduced for the modelling language, an overall workflow along with processes for FHA report and safety requirements generation is presented for the method, and a list of tool constraints is provided. A proof‐of‐concept is subsequently presented using safety data for the landing gear extension and retraction system of a generic business aircraft.

Aircraft landing gear system with magnetorheological shock strut: Performance evaluation via drop test

This work presents a magnetorheological (MR) damper applicable to the landing gear system in the aircraft. The proposed MR landing gear (MRLG) is modeled as a two degrees of freedom (2-DOF) system for the drop performance evaluation. A mathematical model of the governing equations is then formulated considering a flow path whose pressure depends on the major and minor losses. The flow path of MR fluid is composed of annular orifice and bypass as the required damping force for compression and extension is much different, and relief valve operates in conformity with the motion direction of the piston rod. An entry region is added to guarantee precise controllability of the field-dependent damping force. In addition, the magnetic intensity and total loss coefficient are estimated using magnetic analysis and computational fluid dynamics tools, respectively. It is demonstrated from the drop test based on the Federal Aviation Regulation (FAR) Part 23 that the shock struct efficiency (SSE) of the proposed MRLG can be increased from 42% at zero current to 84% at 1 A, and the agreement between simulation and experimental results is excellent showing similar pneumatic force, strut force, and jerk behavior which validates the accuracy of the proposed model.

Shimmy analysis of light weight aircraft nose wheel landing gear

This paper presents mathematical modeling and analysis of shimmy oscillations for a light weight airplane single wheel nose landing gear. Shimmy is a self-excited oscillation which occurs usually on the nose wheel landing gear assembly during ground maneuvers which is governed by the dynamic characteristics of the landing gear and tires. Shimmy oscillation may lead to reduce the fatigue life of the landing gear and fuselage structure. So, the study of dynamic response and stability boundaries of landing gear plays crucial role while designing of airplanes. In earlier studies of vehicle shimmy only 3 degrees of freedom (DOF) considered such as torsional mode, lateral bending mode and tire lateral deformation. In this work along with above mentioned DOF, two more additional DOF introduced such as axial vibration of strut and tire in order to include the effect of vertical dynamics on shimmy model. Gyroscopic coupling effect also included in the model to study its influence on shimmy. Analysis carried out to determine critical velocity region for occurrence of shimmy and to investigate the effectiveness of ground unevenness on the landing gear system for two different runway conditions such as flat runway and random roughness runway. The results are more helpful to study significant interaction between the different parameters of landing gear and to represent stability boundaries.

Structural Analysis of the Nose Landing Gear of a Fighter Aircraft

The landing gear, which is one of the most important mechanical systems in aircraft, is the structure that is exposed to landing loads, one of the most important and critical loads that the aircraft is exposed to throughout its life cycle. In addition to the fact that the landing gear system must have high strength to these loads, long life, high performance, low volume, minimum weight, and low cost are important criteria. For this purpose, the optimum design is created by making a structural analysis using the landing gear finite element method. The main purpose of this study is to analyze the strength criteria by performing the structural analysis of the nose landing gear of a fighter aircraft. For the design, the most critical static and dynamic loads in the landing condition were calculated and applied as vertical, side, and drag forces. The displacement and stress values obtained as the final result by using metallic materials such as Aluminum 7075 T6 alloy, Titanium Ti-6Al-4V alloy, PH13-8Mo, 300M Steel, SAE 1035, and AISI 4340 steel alloy in the nose landing gear fork, torque links, side stay arms, and main strut were compared. The safety of the parts was examined from the results of the analysis. CAD drawings were made using Siemens NX and ANSYS SpaceClaim program. Structural analysis was applied with the ANSYS Workbench program, which uses the finite element method.

Structural optimization and fatigue life analysis of landing gear upper lock

The upper lock is a key component of the landing gear system, and its fatigue life affects its service life and reliability. In this paper, the modal analysis, random vibration analysis, and fatigue life calculation are carried out for the upper lock. According to the analysis results, the upper lock structure is optimized, and the optimization scheme is proposed. The natural frequency, stress, and fatigue life are analyzed, and the scheme meets the design requirements. Finally, the optimized structure is verified to be reasonable and feasible through experiments.

Rancang Bangun Alat Peraga Up Lock Box Pada Nose Landing Gear Pesawat ATR 72 Untuk Media Pembelajaran

Abstract - Airplane is a very important mode of transportation, one of which is ATR aircraft. In this study, the type of aircraft used was the ATR 72-600 aircraft. One of the safety factors that need to be considered on aircraft is the landing gear system. The landing gear system regulates the wheel system on the aircraft for landing and also taking off. Given the importance of ensuring that the plane's wheels are securely locked or not, an up lock box system is needed on the landing gear. In the Up Lock Box system, it is not directly visible from the outside so that the working mechanism is not widely known. This study aims to determine the workings of the up lock box nose teaching aid system on the landing gear and to make a trial up lock box nose teaching aid on the landing gear. The research method begins with a literature study, then looks for design references, namely from the ATA 32 training manual. After that, make a design using the image of the up lock box from the ATR 72 aircraft, assemble the demonstran tool, calibrate and test the demonstran tool. The conclusions in this study are, how the up lock box teaching aids work in accordance with the up lock box working concept in the training manual, the results of the design and manufacture of props accompanied by modifications, as well as the test results on up lock box props in accordance with the up lock work concept box. The size of the props that have been made has a length of 37.8 cm and a width of 16.2 cm.

Fuzzy control of a landing gear system with oleo-pneumatic shock absorber to reduce aircraft vibrations by landing impacts

PurposeThe purpose of this paper is to control a landing gear system with an oleo-pneumatic shock absorber with the fuzzy controller.Design/methodology/approachThe landing gear system with an oleo-pneumatic shock absorber is modeled mathematically. A fuzzy controller is designed for reducing aircraft vibrations. Stroke velocity and main mass velocity parameters were used to decide variable gas pressure with the fuzzy controller.FindingsThe fuzzy controller, designed according to stroke velocity and main mass velocity, reduces aircraft vibrations by the landing impacts. The controller can provide strong robustness because it shows similar good performance for different descent speeds.Research limitations/implicationsThis study was carried out through simulations in a computer environment and has not been experimentally tested in a real environment. In addition, signal and measurement delays are not taken into account. In future models, the effects of these signal delays can be added, and the controller can be tested on a real model.Originality/valueIn this study, to the best of the authors’ knowledge, for the first time, the gas pressure for the landing gear system using an oleo-pneumatic shock absorber was controlled by a fuzzy controller that adjusts the stroke velocity and the main mass velocity. Although the oleo-pneumatic shock absorber model contains high nonlinearities, the designed fuzzy controller gave successful results as robust.

Structural FEM Analyses of a Landing Gear Testing Machine

The “Electro-mechanical Landing gear system Integration for Small Aircraft” (E-LISA) research project has the objective of developing an innovative “iron bird”, a testing facility dedicated to executing tests on an innovative landing gear of a small aircraft. This document presents the structural analyses of this complex testing machine performed with the Finite Element Method (FEM). Key purposes of these numerical simulations were the quantifications of the stress and displacement fields under the loading conditions foreseen for the machine. A modal analysis was performed with the aim of calculating eigenvalues and eigenvectors useful to provide an assessment of the structural dynamic response. The most critical mode shapes and the related frequencies were calculated, and the potentially critical rotational speeds were quantified. Finally, the Peak Stress Method (PSM) was adopted to quantify the fatigue resistance of the most critical weldments and an infinite fatigue life was assessed for the most critical one. The design of the machine, which is currently under manufacturing, was validated by the structural analyses presented here.

The Optimization of Civil Aircraft Product Option Selection Considering the Economy Response with an Improved Non-Dominated Sorting Genetic Algorithm

To serve customized option selection for civil aircraft, a mathematical product option selection optimization model combined with an Improved Non-dominated Sorting Genetic Algorithm for decreasing aircraft fleet maintenance cost was investigated. For airlines, considering the economy and reliability in customized option selection is the most intuitive way to improve aircraft performance to generate the optimal formation configuration. Product option selection usually takes certain indicators as constraints (reliability and economy) to meet and maximize performance through equipment selection (the selected parameters include mean time between failures, price, etc.). To describe the customization needs of airlines by a mathematical model and find the optimal decision through an algorithm, a multi-objective, mathematical product option selection optimization model response with reliability parameters as a decision variable, maintainability as a link, and aircraft fleet maintenance and availability as an objective function is established to serve aircraft option selection in this paper. Next, the multi-objective genetic algorithm is used to solve the model, and the convergence, distribution and fitting accuracy of the objective functions are analyzed. Eventually, the landing gear system is used to verify the effectiveness of the model and method. After optimization, the aircraft fleet maintenance cost is reduced by 20.71%, and the availability is increased by 2.576%. Through the mathematical optimization model, the product configuration is provided for the development of the customization option selection project.

Validation of the safety requirements of the landing gear using fault tree analysis

We analyze the functionality of the landing system of a regional aircraft in the extension and cruise flight modes and validate safety requirements through the fault tree analysis. The main landing gear system is captured in the electromechanical–fluidic domain and system behavior is abstracted in an elementary hydraulic circuit. The functional representation is then constructed into a fault tree which allows analysis of the failure propagation originating at different branch terminals, for instance, at the main landing gear actuator which extends the gear and holds it retracted during the cruise, door actuator, door uplocks, and hydraulic power supply. Each component is assigned a failure probability. Each failure mode is abstracted as a top-level event having a probability of failure and through Boolean combinations of component failures in the lower branches. Two reliability aspects considered are the availability to fully lower the landing gear and the integrity of inadvertent gear or door extension while cruising. Architectural changes through undercarriage system reconfiguration and component redundancy have been exploited to improve system failure rates. The analysis determines the overall system failure rate against the flight cycles. The process is agile to accommodate design changes with the evolution of architecture during the systems engineering lifecycle.

Electromechanical Actuator Design and Control Strategy for UAV Landing Gear

UAV is becoming more and more prevalent not only in the military field but also in the civilian field, whose flight safety and performance is of top concern. The landing gear system is undoubtedly a determining factor in UAV taking off and landing. In recent days, the all-electric trend in UAV design is not irreversible. As a result, the hydraulic actuator is replaced by EMA in the landing system. The electromechanical actuator for UAV landing system is designed in this paper. The detailed actuator system design is introduced in the beginning. And then communication protocol between the actuator system and the flight control computer is presented, serving as the basis of control strategy, which is the main content to study. The control strategy mainly deals with normal landing and emergency landing process. At last, the conclusion part summarizes its applications. The EMA devised in this paper and its corresponding control strategy provide a new idea in the landing system design of UAV.

Simulation of Runway Irregularities in a Novel Test Rig for Fully Electrical Landing Gear Systems

The E-LISA research project, under way within the Clean Sky 2 framework, has the objective of developing an innovative iron bird dedicated to executing tests on the landing gear of a small aircraft transport equipped with an electro-mechanical landing gear and electrical brake. Such tests include the simulation of complete landing procedures under different operating conditions such as runway friction, presence of periodical defects along the runway, variable aircraft weight, and approach speed. To this end, the iron bird requires novel solutions in both its architecture and its control scheme. This paper details an innovative solution that is being implemented in the E-LISA iron bird to enable the execution of tests on a landing gear, reproducing the effects of any type of runway irregularity. First, the rig architecture is presented in detail, with particular care toward the hybrid position/force control system that manages its operations. Then, a simulation model is introduced with the objective of verifying the control system stability and the test rig capability to reproduce on the test articles the effects produced on the landing gear leg of periodical runway irregularities. Simulations results are presented, highlighting the stability of the proposed control scheme and providing a preliminary assessment of the system performances.

Landing gear disassembly sequence planning using multi-level constraint matrix ant colony algorithm


 
 
 The life cycle of most complex engineering systems is greatly a function of maintenance. Generally, most maintenance operation usually requires the removal of failed part. Disassembly sequence planning is an optimization program that seeks to identify the optimal sequence for the removal of the failed part. Most studies in this area usually, use single constraint matrix while implementing varied complex algorithm to identify the optimal sequence that saves time associated with carrying out maintenance operation. The used of single constraint matrix typically has the drawback of computer higher storage requirement as well as time consumption. To address this problem, this study proposes Multi-Level Constraint Matrix Ant Colony Algorithm (MLCMACA). MLCMACA efficiency was validated using complex aircraft landing gear systems in comparison with genetic algorithms. The result shows MLCMACA superior performance from the perspective of reduced search time and faster tracking of optimal disassembly sequence. Hence is recommended for handling of disassembly sequence planning problems.
 
 

Investigation of random runway effect on landing of an aircraft with active landing gears using nonlinear mathematical model

Random runway roughness effect on the dynamic response of an aircraft with landing gears has been investigated using nine degree of freedom nonlinear mathematical model. The developed mathematical model incorporates nonlinear characteristics of air spring stiffness, landing gear damping, tire stiffness and damping of the oleo pneumatic main landing gears and nose gear. Equation of motion for aircraft and each landing gear have been written considering heave, pitch, roll of aircraft and three vertical motions of landing gears respectively for landing response analysis. The equations for longitudinal motion of each landing gear are also written from the mathematical model will be helpful for longitudinal dynamics. The aircraft touchdown and roll on with variable decent velocities on Grade E random runway represented by nonstationary random process. The excitation of different grades of random runway can be considered as stationary random process when the aircraft landing at constant sink velocity. This work mainly focused on finding the dynamic responses of the aircraft such as heave, pitch, roll acceleration, vertical forces and all the three landing gears vertical vibration levels while landing on random runways. The active landing gear system performance is compared with passive landing gear system by numerical simulation in MATLAB/SIMULINK. The investigation using nonlinear model predicted that the effect of active control landing gear provides significant reduction in vibration levels and vertical reactions during landing at various vertical velocities on random runways. To validate the above mathematical model a multi-body dynamics (MBD) model has been simulated in ABAQUS/CAE and the dynamic responses of landing gear forces are compared with those obtained from the nonlinear mathematical model. The nonlinear model responses are also compared with the results of other authors. This study is more useful to adopt active control landing gear in the aircraft to reduce the landing loads transmit on aircraft structure and landing gears due to landing impact. The reduction of vibration levels and vertical forces by the active system increase the fatigue life of landing gears and structural life of airframe.

METERING PIN DIAMETER OPTIMIZATION OF AN AIRCRAFT LANDING GEAR SHOCK ABSORBER

One of the most important components of an aircraft is the landing gear. In today`s modern landing gears, mostly oleo-pneumatic shock struts are used. Analytically, landing gear can be modeled as a mass-spring-damper system. The model used in the study included landing gear components such as the oleo-pneumatic shock strut, tire and wheel. Furthermore, a tapered metering pin was added to model in order to control the area of the orifice by which hydraulic oil flows during the act of landing impact force. Landing gear design usually aims to minimize two elements which are vertical acceleration and displacement of aircraft mass. The impact force during landing is indicated by vertical acceleration. Displacement of shock absorber should be minimum to decrease the size, weight and space needed for the landing gear system. An optimization problem was defined to minimize those two parameters within the range of given inputs. For this purpose, a composite objective function was created to include and optimize the two output parameters simultaneously with equal weight. Among many inputs, metering pin hub and tip external diameters were selected as variables for the optimization and other inputs were kept constant. For the optimization study, genetic algorithm method was coupled with the Matlab/Simulink model of the landing gear model. After some iterations, solution was converged to determine the two diameters of the metering pin where the vertical acceleration and displacement of aircraft mass are minimized as an objective. At the end of optimization process, vertical acceleration of aircraft mass was reduced from 2.433 g to 1.7828 g (-36.47%) within the given constraint of 2 g maximum. Displacement of aircraft mass X1 was increased from 0.2982 m to 0.3682 m (+23.47%) which is in an acceptable limit of 0.4 m.

A New Design Model of an MR Shock Absorber for Aircraft Landing Gear Systems Considering Major and Minor Pressure Losses: Experimental Validation

This work presents a novel design model of a magnetorheological (MR) fluid-based shock absorber (MR shock absorber in short) that can be applied to an aircraft landing gear system. When an external force acts on an MR shock absorber, pressure loss occurs at the flow path while resisting the fluid flow. During the flow motion, two pressure losses occur: the major loss, which is proportional to the flow rate, and the minor loss, which is proportional to the square of the flow rate. In general, when an MR shock absorber is designed for low stroke velocity systems such as an automotive suspension system, the consideration of the major loss only for the design model is well satisfied by experimental results. However, when an MR shock absorber is applied to dynamic systems that require high stroke velocity, such as aircraft landing gear systems, the minor loss effect becomes significant to the pressure drop. In this work, a new design model for an MR shock absorber, considering both the major and minor pressure losses, is proposed. After formulating a mathematical design model, a prototype of an MR shock absorber is manufactured based on the design parameters of a lightweight aircraft landing gear system. After establishing a drop test for the MR shock absorber, the results of the pressure drop versus stroke/stroke velocity are investigated at different impact energies. It is shown from comparative evaluation that the proposed design model agrees with the experiment much better than the model that considers only the major pressure loss.

Semi-Active Control for a Helicopter with Multiple Landing Gears Equipped with Magnetorheological Dampers

Due to their extensive use in various applications, helicopters need to be able to land in a variety of conditions. Typically, a helicopter landing gear system with skids or passive wheel-dampers is designed based on only one critical touchdown condition. Thus, this helicopter landing gear system may not perform well in different landing conditions. A landing gear system with magnetorheological (MR) dampers would be a promising candidate to solve this problem. However, a semi-active controller must be designed to determine the electrical current applied to the MR damper to directly manage the damping force. This paper presents a new skyhook controller, called the skyhook extended controller, for a helicopter with multiple landing gears equipped with MR dampers to reduce the helicopter’s acceleration at the center of gravity in off-normal landing attitude conditions. A 9-DOF simulation model of a helicopter with multiple MR landing gears was built using RECURDYN. To verify the effectiveness of the proposed controller, co-simulations were executed with RECURDYN and MATLAB in different initial pitch and roll angles at touchdown. The main simulation results show that the proposed controller can greatly decrease the peak and rms acceleration of the helicopter’s center of gravity compared to a traditional skyhook controller and passive damper.

쿼드콥터의 험지 착륙을 위한 적응형 랜딩 시스템 연구

In this paper, we propose an adaptive four-leg landing system for a quadcopter to enable stable landing on inclined surfaces or rough terrain while maintaining its attitude. A rotorcraft has a disadvantage in that it must have a flat ground for landing because the existing landing gear system is fixed and cannot be changed according to ground conditions. The proposed adaptive landing system makes it possible for a quadcopter to operate in various environments with minimal sensors. For this purpose, a four-leg landing system with two degrees of freedom having a two-link structure was manufactured. Through kinematic analysis of the landing leg, the coordinates of the joint and end-effector were identified, and an equation for horizontal control was established. When landing on the slope, the ground surface was detected using force sensors, attached at the end of each leg. Adaptive landing control was performed according to the roll and pitch values of the inertial measurement unit sensor mounted on the quadcopter. The proposed system was pre-validated in the simulation environment of Matlab Simulink. The superiority of the proposed system was verified experimentally in various environments. In an indoor environment, the effectiveness of the system was verified in a situation where it landed at a constant speed using a testbed. Finally, the system stability was verified through flying and landing of the quadcopter in an outdoor environment.

Robust force and displacement control of an active landing gear for vibration reduction at touchdown and during taxiing

In this paper, a new approach is proposed to control the dynamic response of a landing gear system subjected to runway force, both on heavy landing conditions and at the taxiing process. The mathematical model of the system is used in a way that covers nonlinear dynamics characteristics of landing gear and nonlinear/nonaffine property of the external actuator. The operation of the landing gear system and its components are described briefly. The desired control system includes two different interior loops for displacement and force control. The inner loop determines the actuator force and the outer loop performs the displacement control. A lumped uncertainty is considered in both displacement and force control loops that represent uncertainties including parametric errors, measurement noises, unmodeled dynamics, disturbance due to runway excitation, and other disturbances. The direct method of Lyapunov is utilized for asymptotic stability analysis of the robust nonlinear control system (RNCS). This system is simulated in MATLAB software and the performance of the proposed controller is analyzed exactly. Besides, the results are compared with a passive system and conventional PID control. The comparison indicates that RNCS works better and more precisely. This method can reduce vibrations at touchdown and taxiing and effectively overcome uncertainty and provide well aircraft handling by decreasing the changes in tire force.