Nose Landing Gear Research Articles

Failure analysis of a nose landing gear fork

Abstract This paper presents a detailed analysis of a nose landing gear failure. The developed study comes following an accident occurred in which the nose of the landing gear's fork of a light aircraft failed during landing. According to Federal Aviation Administration, in average, 55% of aircraft failures occur during takeoff and landing. In order to determine the causes of the accident, a material analysis was performed, followed by a detailed study of the fracture's surface both visually and using optical and scanning electron microscopies. It was observed that fatigue cracks developed in the vicinity of the bolted holes, which work as supporting connections, on the topside of the nose fork and, as such, it can be concluded that the referred area was subjected to cyclic stresses originating and propagating cracks in the material. This cracking is characteristic of the existence of stress concentration areas. Identified the crack initiation zone with ratcheting and beach marks near the origin of the crack, combined with the fact that the nose wheel fork is subject to cyclic loading, leads to the conclusion that the component failed due to fatigue. Finite element analyses were also performed on the nose fork taking into account service conditions in order to assess the structural integrity of the component. During the analysis it was observed that the critical areas are located in the vicinity of the connecting holes, as it was observed in the fracture surface analysis. The assembly behavior in the presence of four straight cracks, originating from the fork holes, was also studied using the stress intensity factors, calculated using the contour integral method.

A robust active control system for shimmy damping in the presence of free play and uncertainties

Shimmy vibration is the oscillatory motion of the fork–wheel assembly about the steering axis. It represents one of the major problem of aircraft landing gear because it can lead to excessive wear, discomfort as well as safety concerns. Based on the nonlinear model of the mechanics of a single wheel nose landing gear (NLG), electromechanical actuator and tire elasticity, a robust active controller capable of damping shimmy vibration is designed and investigated in this study. A novel Decline Population Swarm Optimization (PDSO) procedure is introduced and used to select the optimal parameters for the controller. The PDSO procedure is based on a decline demographic model and shows high global search capability with reduced computational costs. The open and closed loop system behavior is analyzed under different case studies of aeronautical interest and the effects of torsional free play on the nose landing gear response are also studied. Plant parameters probabilistic uncertainties are then taken into account to assess the active controller robustness using a stochastic approach.

Investigation into the Interaction of Nose Landing Gear and Fuselage Dynamics

Pilots may experience vibrations in the cockpit during ground maneuvers because of energy being transferred from the nose landing gear to the fuselage. This indicates that the fuselage dynamics could also have an effect on the dynamics of the gear. To study this interaction, a mathematical model of a nose landing gear coupled to a fuselage model with yaw and pitch degrees of freedom is developed. Results obtained by bifurcation analysis show the nature of the interaction between the two systems; in particular, the two-degree-of-freedom fuselage does affect the onset and subsequent severity of nose landing gear shimmy.

Fault Analysis and Solution of an Airplane Nose Landing Gear’s Emergency Lowering

In this paper, the fault analysis of an aircraft nose landing gear’s emergency lowering was conducted with a cosimulation method. The simulation was aimed at studying the dynamic response characteristics of landing-gear retraction/extension. Moreover, the equations of the mechanical and hydraulic system were derived and analyzed so as to acquire the boundary condition under which the landing-gear emergency lowering could fail. Based on the simulation platform computer aided engineering, a cosimulation model (including a dynamic system and a hydraulic system) was developed, after which, by comparing the simulation results with the data of the ground test and flight test, the model was further verified. Additionally, the nose landing gear could succeed in emergency lowering with the premise that the critical dampings of different flight cases and temperatures were obtained. After that, a feasible scheme of emergency lowering was put forward. The results showed that, at the end of the landing-gear lowering process, the favorable moment saltation produced by the spring force could lag behind the unfavorable moment saltation of the aerodynamic force of the front and back cabin doors, thus resulting in the fault of emergency lowering and locking. Furthermore, when the method of decreasing the damping force was adopted, the landing gear would succeed in emergency lowering only by adjusting the force down to the critical value. However, due to the reduced damping force, the lowering process could be made so fast that there was a great impact load on the landing gear at the end of the trip. The solution laid in using the original damping value in normal extension and the reduced damping value in emergency lowering by a hydraulic selector valve.

Bifurcation Study of a Dynamic Model of a Landing-Gear Mechanism

This paper presents a new modeling approach for the analysis of landing-gear mechanisms. By replacing the mechanism’s rotational joints with equivalent high-stiffness elastic joints, numerical-continuation methods can be applied directly to dynamic models of landing-gear mechanisms. The effects of using elastic joints are considered through two applications: an overcenter mechanism and a nose-landing-gear mechanism. In both cases, selecting a sufficient stiffness for the elastic joint is shown to provide accurate continuation results. The advantages of this new modeling approach are then demonstrated by considering the unlocking of a nose landing gear with a single uplock/downlock mechanism, when subjected to different orientations and magnitudes of gravitational loading. The unlocking process is shown to be qualitatively insensitive to changes in both load angle and load magnitude, ratifying the robustness of a previously proposed control methodology for unlocking a nose landing gear with a single uplock/downlock mechanism.

Measuring of a Nose Landing Gear Load during Take-Off and Landing

This article provides information about in-flight measurement of a small sport aircraft. The strain gauges were used as sensors for load monitoring on the nose landing gear structure. To obtain overall forces it was necessary to do the calibration procedure. After the calculation of strain gauge coefficients the equations for calculating of total force, total force direction and individual force components were determined. During test flights the data acquisition system was installed into the aircraft. The data from strain gauges were collected together with other flight parameters like speed, altitude and data from inertial measurement unit which determined the exact movements of the aircraft before landing. The data recorded during fifty-six flights were analysed to obtain loads acting in the aircraft structure. These results were compared with calculated values.

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.

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.

Method for modeling and simulation of aircraft taxiing with unilateral and non-holonomic constraints

The motion of the aircraft taxiing along the ground was related to wind load and asymmetric braking torque. The method for modeling and simulation of the aircraft was presented on the basis of the dynamics of the non-smooth multibody system with non-holonomic constraints in order to analyze the dynamic behavior of the aircraft taxiing along the ground. The aircraft was treated as the multibody system which consisted of a rigid fuselage,two wheels of main landing gears and a wheel of nose landing gear. Two wheels of main landing gears rolled on the ground without slip. The lateral slip of the wheel on the nose landing gear was taken into account when the aircraft taxied along the ground. The dynamic equations of the system were obtained by Routh 's equations and the constraint-stabilized method to reduce constraint drift. The frictional model between the wheels and the ground was the model of Coulomb friction which was described by the set value of function to determine whether the wheel of the nose landing gear slipped in lateral direction or not. Finally,numerical examples were presented to analyze the dynamic behavior of the aircraft undertook the wind load and the asymmetric braking torque.

Design and Analysis Aircraft Nose and Nose Landing Gear

Tri-cycle arrangement landing gear is extensively used as it is simple; convenient both structurally as well as aerodynamically. Though it is advantageous over other configuration is has its own draw backs. Factors like its weight drag, sudden application of load, acoustics, fatigue etc tend to slow down its performance and life. Among main landing gear and nose landing gear; the former carries about 85% of total weight of aircraft and latter carries around 12-15% of weight. The nose landing gear is also a source of noise and its effect is prominent when compared to main landing gear. In this project the executive jet aircraft are studied thoroughly and a nose landing gear similar to those of executive jets is modeled using CATIA. The same geometry is imported to ANSYS ICEM and flow on the body is analyzed for different angle of attack. Pressure variation, temperature, density and velocity distribution around the body is noted and then Coefficient for Lift and Drag are plotted against angle of attack for obtained results. It is also important to check the strength and stiffness of designed landing gear. Hence using ANSYS APDL and Explicit; Static structural and Impact test has been carried out for designed geometry. Stress distribution and deformation was noted for two distinct materials such as steel and aluminum alloy and primary results of acoustics has been compared with the available data.

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.

The Load Simulation Research of Nose Landing Gear Steering

The nose landing gear is a vital component of an aircraft,which has an important impact on the safety of the aircraft.This paper studies the system of nose landing gear steering on the basis of the gear and rack mechanism durability test of a certain type of civil aircraft landing gear steering. Furthermore,it puts forward a method of passive loading,which can simulate the friction when the nose landing gear reciprocating turning,and establishes the mathematical model. The simulation results show that the simulator can meet the requirements of load,and laid a theoretical foundation for the subsequent actual work.

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.

English

Future Green Regional Aircraft (GRA) will operate over airports located in the neighborhood of densely populated areas, with high frequency of takeoff/ landing events and, hence, strongly contribute to community noise and gaseous emissions. These issues currently limit further growth of traffic operated by regional airliners which, in the next future, will have to face even more stringent environmental normative worldwide and therefore re-designed to incorporate advanced active aerodynamic technologies. The new concept behind GRA is based on several mainstream technologies: airframe low-noise (LN), aerodynamic load control (LC) and load alleviation (LA). These technologies integrate relevant concepts for hybrid and natural laminar flow (HLC/NLF) wing, active control of wing movables and aeroelastic tailoring for LC/LA functions, passive means (micro-riblets) for turbulent flow drag reduction, innovative gapless architectures (droop nose, morphing flap) beside conventional high-lift devices (HLDs), active flow control through synthetic jets, low-noise solutions applied to HLDs (liners, fences), and to fuselage-mounted main and nose landing gears (bay/doors acoustic treatments, fairings, wheels hub cap). The paper deals with the technological readiness level (TRL) assessment of the most promising technologies and overall integration in the new generation of GRA, as a highly optimized configuration able to meet requirements for FlighPath 2050.

Runway debris impact threat maps for transport aircraft

AbstractLarge transport aircraft are particularly susceptible to impact damage from runway debris thrown up by the landing gear. A methodology was developed to predict the trajectories of stones lofted by the nose wheel and subjected to aerodynamic forces due to the wake behind the nose landing gear and beneath the aircraft. In conjunction with finite element modelling of the stone/ground/tyre contact mechanics, an analytical model was used to perform a stochastic prediction of the trajectories of runway stones to generate impact threat maps which showed the relative likelihood of stones impinging upon various areas on the underside of a C-130 Hercules. The impact envelopes for the C-130 extended three to eighteen metres behind the nose wheel and two metres either side of the centre of the aircraft. The impact threat maps were especially sensitive to the values of the coefficients of lift and drag acting on the stone during its flight.

Design and Stress Analysis of Nose Landing Gear Barrel (NLGB) of a typical naval trainer aircraft

During the conceptual design phase of aircraft the integration of undercarriage system is very important and it is often difficult to achieve on the first time. The nose wheel landing gear preferred configurations for light naval trainer aircraft. The main objective of this project is to improve the static strength criteria and fatigue life of Nose Landing Gear Barrel considered. The investigations includes preliminary design layout for Nose Landing Gear Barrel and initial sizing has been done. It has been designed and evaluated for strength criteria. A method of analysis for the design of Nose Landing Gear Barrel made up of Al-Cu alloy (BS L 168 T6511) with static loads of axial, bending and normal loads are applied. The geometric modeling of the Nose Landing Gear Barrel was carried out using CAD package CATIA V5 R19 and pre and post processing was done through MSC/PATRAN. The stresses and displacements are obtained with the application of MSC/NASTRAN finite element software. I. INTRODUCTION The Landing gear is the structure that supports an aircraft on the ground and allows it to taxi, take-off and land .The Landing gear system consists of the main landing gear and nose landing gear. Each landing gear includes a shock strut with two and tire assemblies. Tires and the wheel absorbs the original impact on landing and are the principal part of the aircraft involved in the ground control. It allows more forceful application of the brakes without the danger of nosing the aircraft over. Tricycle is the most widely used landing gear configuration. The wheels aft of the aircraft cg is very close to it and carries much of the aircraft weight and load, thus is referred to as the main wheel. Two main gears are in the same distance from the cg in the x-axis and the same distances in y-axis, thus both are carrying the same load. The forward gear is far from cg, hence it carries much smaller load. The share of the main gear from the total load is about 80 to 90 percent of the total load, so the nose gear is carrying about 10 to 20 percent. This arrangement is sometimes called nose-gear. Both main and nose gears have the same height, so the aircraft is level on the ground, although the main gears often tends to have larger wheels. This allows the floor to be flat for passenger and cargo loading. Unlike tail-gear, a nose gear configuration aircraft is directionally stable on the ground as well as during taxing. The reason is that if the aircraft yaws slightly while taxiing, the rolling and skidding resistance of the main gear, acting behind the cg, tends to straighten the aircraft out.

Bifurcation Analysis of a Coupled Nose-Landing-Gear–Fuselage System

Under certain conditions during takeoff and landing, pilots may sometimes experience vibrations in the cockpit. Because the cockpit is located right above the nose landing gear, which is known to potentially be prone to self-excited vibrations at certain velocities, an explanation for those vibrations might be oscillations of the landing gear feeding into the fuselage. However, the fuselage dynamics itself may also influence the dynamics of the landing gear, meaning that the coupling must be considered as bidirectional. A mathematical model is developed to study a coupled nose-landing-gear–fuselage system, which allows to assess the overall influence of the coupling on the system dynamics. Bifurcation analysis reveals that this interaction may be significant in both directions and that the system behavior depends strongly on the modal characteristics of the fuselage.

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.

Application of a magnetorheological damper modeled using the current–dependent Bouc–Wen model for shimmy suppression in a torsional nose landing gear with and without freeplay

In this study, shimmy of a nose landing gear model with torsional degree of freedom is analyzed. Equations governing the torsional nose landing gear model and the stretched string tire model are presented. Freeplay is incorporated into the model. A magnetorheological (MR) damper modeled using the current–dependent Bouc–Wen model is introduced to the torsional landing gear model with and without freeplay. Parameter identification of the Bouc–Wen model is accomplished using genetic algorithms. Incorporation of an MR damper into the landing gear model with and without freeplay is the advantage in this study. Implementation of the current–dependent Bouc–Wen model in such a landing gear model is another brand new concept.

Dynamic Landing Response Analysis of a Flexible Tailless Delta Wing Aircraft

Modern tailless delta wing aircraft is built for high performance with light weight leading to structural flexibility. During landing, high vertical sink rate of aircraft causes peak transient loads in and around the landing gear attachment locations. These reactions forms the load cases for local sizing of airframe and its responses determine the overall integrity. This paper describes the co-simulation approach to carry out the dynamic landing analysis on a flexible tailless delta wing aircraft and examines the responses at certain critical locations such as the tip of wings, fin and nose for nominal landing conditions. The reactions are obtained from the Landing gear supplier through MSC Adams multi-body dynamic simulation of full aircraft with non-linear stiffness and damping models of Nose and Main landing gear systems. The landing response analysis is carried out on a flexible aircraft using industry standard MSC Nastran as transient dynamic problem with base enforced motion. It is observed that the...