Aircraft Nose Landing Gear Research Articles

Structural Strength Analysis and Optimization of Commercial Aircraft Nose Landing Gear under Towing Taxi-Out Conditions Using Finite Element Simulation and Modal Testing

In the field of civil aviation, the nose landing gear is a critical component that is prone to damage during taxiing. With the advent of new technologies such as towing taxi-out and hub motors, the nose landing gear faces increasingly complex operational environments, thereby imposing higher performance demands. Ensuring the structural safety of the nose landing gear is fundamental for the successful application of these technologies. However, current research on aircraft nose landing gear under these new conditions is somewhat lacking, particularly in terms of reliable analysis models for real-world scenarios. This study focuses on a typical Class C aircraft, specifically the B-727 model, for which a finite element model of the nose landing gear is developed. Modal testing of the aircraft’s nose landing gear is conducted using the impact hammer method, and the results are compared with those from the simulations. The experimental data indicate that the error range for the first seven natural frequencies is between 0.23% and 9.27%, confirming the high accuracy of the developed landing gear model. Furthermore, with towing taxi-out as the primary scenario, a dynamic model of the aircraft towing system is established, and an analysis on the structural strength and topological optimization of the nose landing gear under various conditions, including high speeds and heavy loads, is performed. The results show that the developed model can effectively support the analysis and prediction of the mechanical behavior of the nose landing gear. Under high-speed, heavy-load conditions, the nose landing gear experiences significantly increased loads, with the maximum deformation primarily occurring at the lower section of the shock strut’s outer cylinder. However, no damage occurred. Additionally, under these conditions, an optimized structural design for the landing gear was identified, which, while ensuring structural strength, achieves a 22.32% reduction in the mass of the outer cylinder, also ensuring safety in towing taxi-out conditions.

Landing Impact Load Analysis and Validation of a Civil Aircraft Nose Landing Gear

Landing impact load design is essential, but the process has rarely been fully described, and some designers have even neglected the differences between wheel-axle and ground-contact loads, as well as loads in the longitudinal direction, especially in experimental validations. In this paper, the entire design process of a nose landing gear is addressed, including a theoretical analysis of the unit and its experimental validation. In the theoretical analysis, a mathematical model of a two-mass system with four degrees of freedom was adopted, a computer simulation model was built accordingly, and a preliminary analysis was subsequently conducted to analyze the landing impact loads, verify the landing gear performance, and gauge the difference between the wheel-axle and ground-contact loads. For the experimental validation of the gear, a landing gear drop test was conducted in an optimized manner that emphasized pre-test preparation and during-test wheel-axle load measurement. The test results showed that both the vertical and less studied longitudinal loads, as well as the wheel-axle and ground-contact loads, had good agreement with the analysis; thus, the model, the tool, and the preliminary design were considered to be experimentally validated.

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.

Shimmy Suppression of an Aircraft Nose Landing Gear Using Torsional Nonlinear Energy Sink

Abstract Shimmy motion may occur for an aircraft nose landing gear (NLG) during its takeoff, landing, and taxiing procedure, which is an undesirable motion and should be suppressed. Here, a novel torsional nonlinear energy sink (NES) based on the cam-roller mechanism is proposed and applied in the NLG to improve its shimmy performance. The torsional NES is connected with the upper and lower struts of the NLG and its mechanical characteristic is studied. A seven-dimensional dynamic model of the NLG coupled with NES is built, which considers the NLG torsional and lateral motions, and the nonlinear tire model. The numerical continuation method is applied to analyze its shimmy performance, the stable area and limit cycle oscillation (LCO) amplitude are acquired, further compared with those of the original NLG without using the NES. The results show that as the NES is used in the NLG, the torsional shimmy dominated unstable area reduces significantly and the lateral shimmy dominated unstable area decreases slightly, which results in the increase of the stable area of the NLG; the maximum LCO amplitudes for the NLG torsional and lateral shimmy become smaller, the forward speed ranges as the torsional and lateral shimmy occur become narrower, which indicates that the stable forward speed ranges of the NLG become wider; the NLG shimmy performance improves as the NES has larger torsional inertia and damping, and smaller torsional linear stiffness. Thus, the NES can suppress the NLG shimmy motion and enhance its shimmy performance effectively.

Topology optimization of Nose Landing Gear of Aircraft for weight reduction

Design, Analysis, test and validation process of a NLG brace assembly of aircraft is mentioned in this study. The Nose Landing Gear is designed with for the purpose of attaching landing gear and wheel Moreover works on weight reduction, cost reduction. Key Word: ANSYS, NLG.

Using nonlinear feedback control to improve aircraft nose landing gear shimmy performance

Using nonlinear feedback control to improve aircraft nose landing gear shimmy performance

Selection Methodology of an Electric Actuator for Nose Landing Gear of a Light Weight Aircraft

Landing gear system of an aircraft enables it to take off and land with safety and comfort. Because of the horizontal and vertical velocity of aircraft, upon landing, the complete aircraft undergoes different forcing functions in the form of the impact force that is absorbed by landing gears, shock absorbers, and actuators. In this research, a selection methodology has been proposed for an electrical actuator to be installed in the retraction mechanism of nose landing gear of an aircraft having 1600 kg gross takeoff weight. Nose landing gear and its associated components, like strut and shock absorbers, were modeled in CAD software. Analytical expressions were then developed in order to calculate the actuator stroke, translational velocity, force, and power for complete cycle of retraction, and some were subsequently compared with the computational results that were obtained using MSC ADAMS®. Air in the oleo-pneumatic shock absorber of nose landing gear was modeled as a nonlinear spring with equivalent spring constant, whereas hydraulic oil was modeled as a nonlinear damper with equivalent damping constant. The nose landing gear system was modeled as a mass-spring-damper system for which a solution for sinusoidal forcing functions is proposed. Finally, an electrical actuator has been selected, which can retract and extend nose landing gear, meeting all of the constraints of aircraft, like fuselage space, aircraft ground clearance, locking loads, power consumption, retraction and extension time, and dynamic response of aircraft. It was found that the selection of an electrical actuator is based upon the quantification of forces transmitted to electrical actuator during one point load at gross takeoff weight. The ability of retraction and extension time, as dictated by Federal Aviation Regulation, has also been given due consideration in the proposed methodology as significant criteria. The proposed system is now in the process of ground testing, followed by flight testing in the near future.

Nose Landing Gear Simple Adaptive Shimmy Suppression System

The occurrence of shimmy vibration in aircraft nose landing gear can cause an increase of fatigue stress on the nose landing gear mechanical elements that can eventually lead to high wearing of components as well as to severe damage of the leg, giving raise to safety issues. The use of the Modified Simple Adaptive Controller is investigated for the realization of an adaptive shimmy suppression system. The nonlinear governing equations that model the shimmy vibration behavior of an aircraft nose landing gear are first linearized in order to synthesize the adaptive controller, while nonlinear terms are then taken into account as disturbances. The almost strict passivity of the plant is obtained by using a parallel feedforward compensator. The parallel feedforward compensator is designed as the inverse of a stabilizing controller while the Modified Simple Adaptive Controller is tuned by considering the minimization of some dynamic performance parameters as design requirements. The influence of the advancing speed on the controlled plant response is studied by simulating scenarios of aeronautical interests.

Design of a five‐phase permanent‐magnet motor for the electric steering of an aircraft nose landing gear

Recently, there has been a growing interest in reducing the number or replacing the hydraulic/pneumatic actuators utilised on aircraft with electric actuators coupled to mechanical gears, which would improve the reliability and performance. This is involved in the concept of more electric aircraft. The electrification of actuators would affect the primary and secondary flight controls, as well as the movement of flight surfaces, retraction of the landing gear, and steering of the nose landing gear, which is also considered in this study. This study considers the design of a multiphase permanent-magnet (PM) motor to be utilised for the electric steering of a commercial aircraft nose landing gear. This multiphase motor would make it possible to achieve a highly reliable actuator and, coupled with a harmonic drive, avoid the use of a multi-motor configuration. Moreover, a multiphase motor would increase the power density and efficiency of the actuator, through improving the torque ripple. The performance variation due to temperature swings is considered, and a design procedure for the PM motor is described using the worse operation case for the electric actuator. The adequate performance of the designed motor and actuator is demonstrated by means of a finite element analysis.

Robust and optimal control of shimmy vibration in aircraft nose landing gear

Shimmy vibration of aircraft nose landing gear is damped and controlled using a nonlinear control which is optimal and robust against parametric uncertainties and external disturbances. Shimmy vibration is the lateral and torsional vibrations in the wheel of the aircraft that is self-excited and causes instability in high speed performances which can damage the landing gear of the aircraft, its fuselage and even may result in hurting the passengers. Thus, control and damping of this vibration are extremely important. In this paper a robust optimal controller is designed by integrating sliding mode control (SMC) together with State-Dependent Riccati Equation (SDRE) to prevent the shimmy vibrations in aircraft nose landing gear. The SDRE compensator controls the nonlinear system in an optimal way while the sliding mode controller guarantees its stability against uncertainties and disturbances. The proposed controller can effectively suppress the shimmy vibration of the landing gear with variable taxiing velocity and wheel caster length. To verify the optimal performance and robustness of the proposed controller, vibration response of the system is simulated by MATLAB software and its performance and efficiency are verified using comparative analysis. Considerable improvement can be seen in the performance of the closed loop system since not only the vibrations are effectively damped but also the consumption of energy is minimized.

A bifurcation study to guide the design of a landing gear with a combined uplock/downlock mechanism.

This paper discusses the insights that a bifurcation analysis can provide when designing mechanisms. A model, in the form of a set of coupled steady-state equations, can be derived to describe the mechanism. Solutions to this model can be traced through the mechanism's state versus parameter space via numerical continuation, under the simultaneous variation of one or more parameters. With this approach, crucial features in the response surface, such as bifurcation points, can be identified. By numerically continuing these points in the appropriate parameter space, the resulting bifurcation diagram can be used to guide parameter selection and optimization. In this paper, we demonstrate the potential of this technique by considering an aircraft nose landing gear, with a novel locking strategy that uses a combined uplock/downlock mechanism. The landing gear is locked when in the retracted or deployed states. Transitions between these locked states and the unlocked state (where the landing gear is a mechanism) are shown to depend upon the positions of two fold point bifurcations. By performing a two-parameter continuation, the critical points are traced to identify operational boundaries. Following the variation of the fold points through parameter space, a minimum spring stiffness is identified that enables the landing gear to be locked in the retracted state. The bifurcation analysis also shows that the unlocking of a retracted landing gear should use an unlock force measure, rather than a position indicator, to de-couple the effects of the retraction and locking actuators. Overall, the study demonstrates that bifurcation analysis can enhance the understanding of the influence of design choices over a wide operating range where nonlinearity is significant.

Effect of Torsional Damping on Aircraft Nose Landing-Gear Shimmy

The bifurcation analysis method is applied in dealing with shimmy oscillations of the aircraft nose landing gear. Algorithms and details of the procedure in bifurcation analysis are described. Torsional damping of the antiswing damper is studied based on the model consisting of torsional and lateral bending modes of the landing gear. It is concluded that more linear torsional damping means more stability from torsional shimmy, although excessive damping will result in lateral shimmy at the starting speed and low vertical force. The torsional shimmy occurs prior in the area of low speed and midvertical force without sufficient linear damping. And there exists a so-called ideal damping varying with forward speed, with which no shimmy happens in the global scope below a critical vertical force. Squared torsional damping has little influence on the area of shimmy unless Bautin bifurcation appears in the dynamics system, and it is effective in controlling the amplitude of shimmy oscillations. The torsional clearance increases the unstable area of torsional shimmy obviously, but the value of the clearance does not affect the shimmy area.

Modeling and Faults Simulation of Aircraft Landing Gear System

The model of aircraft landing gear hydraulic system is build by software of AMESim. Under the AMESim environment, a hydraulic simulation of the nose landing gear of aircraft is constructed. The simulation model of the component is built by graphical modeling method. Setting two case faults parameters of landing gear actuating cylinder leakage and air into oil, it obtains faults symptom of hydraulic system. The Internal characteristics, Interrelation and motion Law is shown for landing gear system various components. Combining hydraulic system simulation with fault diagnosis effectively, it can provide reference for fault analysis and design improvement of landing gear hydraulic system.

Modeling and Simulation of Aircraft Nose Landing Gear Emergency Lowering Using Co-Simulation Method

This paper builds dynamical models and hydraulic system models of retraction/lowering of some regional aircraft nose landing gear respectively based on the software LMS VL motion and AMESim. The simulation analysis result was proved to be credible by checking with that of ground test. The peak oil return pressure with the critical damping force can be obtained by analyzing the hydraulic damping characteristic of actuator cylinder during landing gear emergency lowering based on methods of estimation and co-simulation. The results indicate that the damping characteristic of actuator cylinder plays an important role in emergency lowering. Only when the damping force breaks through the critical value, can the landing gear succeed in emergency lowering and being locked. However, the little damping force will result in great impact load while lowering. Thus, damping force should be changed only when emergency lowering.

Vibration control of an aircraft nose landing gear due to ground-induced excitation

The effects of runway unevenness on the design and operation of an aircraft have been subjected to investigations for a number of years. Runway roughness will, in general, produce both longitudinal and lateral excitations. This article examines the lateral stability of linear and non-linear models of an aircraft nose landing gear (NLG) subjected to ground-induced lateral excitation. Simulations of ground profile and ground excitation modelling have been performed and numerical studies were carried out to bring out the effect of runway roughness and its interaction with torsional free play. The results show that a small amount of runway excitation causes a significant reduction in the critical shimmy velocity and, in combination with free play, it has an adverse impact on lateral stability of the NLG of an aircraft. Finally, a study has been performed to postpone the dynamic instability by introducing a magnetorheological (MR) fluid-based damper and enhanced torque arm stiffness.

Interaction of torsion and lateral bending in aircraft nose landing gear shimmy

In this paper we consider the onset of shimmy oscillations of an aircraft nose landing gear. To this end we develop and study a mathematical model with torsional and lateral bending modes that are coupled through a wheel-mounted elastic tyre. The geometric effects of a positive rake angle are fully incorporated into the resulting five-dimensional ordinary differential equation model. A bifurcation analysis in terms of the forward velocity and the vertical force on the gear reveals routes to different types of shimmy oscillations. In particular, we find regions of stable torsional and stable lateral shimmy oscillations, as well as transient quasiperiodic shimmy where both modes are excited.

Analysis of the specific features of loading of the elements of landing gears of aircrafts aimed at the evaluation of the load-bearing capacity of the structure

We propose a computational scheme of the aircraft nose landing gear and perform the analysis of weak sections in the landing-gear lever by the finite-element method. We determine the loading modes in which the landing-gear lever is subjected to disproportional cyclic loads, which should be taken into account in the evaluation of the service life and determination of the properties of applied materials.

ADAMS를 이용한 항공기 전륜착륙장치의 동적거동해석 및 최적설계

본 연구에서는 KT-1 계열 항공기 전륜착륙장치의 동적거동을 분석하고 충격흡수효율을 향상시키기 위한 완충기의 최적설계가 수행되었다. 전륜착륙장치는 ADAMS를 이용하여 2자유도계로 모델링하였으며 운영/환경 조건을 고려한 해석결과는 낙하실험결과와 잘 일치하였다. 또한 최적설계변수를 선정하기 위해 오일밀도, 오리피스 단면적과 같은 완충기 파라미터를 변화시켜 동적거동 및 충격흡수효율에 미치는 영향을 분석하였으며, 해석 결과 완충기 파라미터가 다른 파라미터들보다 큰 영향을 미쳤다. 유용방향탐색법을 사용하여 최적설계를 진행하였고, 최대효율을 나타낼 때 설계변수의 값을 산출하였다. 이러한 방법으로 전륜착륙장치의 최적설계를 통해 충격흡수효율과 동적거동능력을 향상시킬 수 있었다. The dynamic behaviors of a KT-1 family aircraft nose landing gear have been analyzed and the optimal design of an aircraft shock absorber has been conducted to improve efficiency of shock energy absorption. The nose landing gear is modeled as a 2 DOF system using ADAMS and various operational and environmental landing conditions were considered. The results of dynamic simulation for various landing conditions agree well with experiments. Also the effect of parameters of a shock strut on the dynamic behaviors and on shock energy absorption of the nose landing gear has been evaluated for optimal design to define design variables. It has been found that the parameters of a shock strut such as oil-density and orifice area have more effects on dynamic behaviors than those of operation conditions. Optimal design is performed to maximize the efficiency of shock energy absorption using Feasible Direction Method. As a result the design values of the shock strut for maximum efficiency of shock energy absorption are derived and it turns out that efficiency and dynamic behaviors of the nose landing gear were improved by the optimal design.