Showing papers on "Landing gear published in 2021"

Nonlinear energy sink to enhance the landing gear shimmy performance

Abstract: The shimmy phenomenon is a significant concern in aircraft landing gear dynamics. The prediction of the shimmy instability is an essential issue in landing gear design to develop a passive or active suppression method. This work investigates the application of the nonlinear energy sink (NES) concept to mitigate the effects of shimmy in landing gears. The NES concept has been used in recent research on mechanical vibrations. It comprises a passive target energy transfer method that refers to a one-way energy transfer from a primary to a nonlinear subsystem. The landing gear model is based on torsional displacement coupled with the tyre classical elastic string analogy model. The NES device connects to the wheel shaft, and it comprises a mass, a linear damper, and a pure cubic spring. The numerical integration in time was used to assess the shimmy onset speed and the post-shimmy limit cycle oscillations. A parametric analysis of the landing gear nonlinear dynamics without the NES is presented. The design space of possible NES parameters is given, obeying design constraints, and inspected to assess adequate NES designs. The best NES samples are included in the landing gear dynamics to study their influence. Results have shown that the NES can adequately expand the operational speed range for no shimmy and lead to lower LCO amplitudes in the post-shimmy for a reasonable range of speeds. The NES concept’s successful employment for the landing gear dynamics suggests an enormous potential form of passive shimmy control.

Landing efficiency control of a six-degree-of-freedom aircraft model with magnetorheological dampers: Part 1—Modeling:

Abstract: This work presents landing efficiency control of a six-degree-of-freedom aircraft model, which has a controllable landing gear system with magnetorheological damper. Due to lengthy contents, this w...

Vibration Response Aspects of a Main Landing Gear Composite Door Designed for High-Speed Rotorcraft

Abstract: One of the crucial issues affecting the structural safety of propeller vehicles is the propeller tonal excitation and related vibrations. Propeller rotation during flight generates vibrating sources depending upon its rotational angular velocity, number of blades, power at shaft generating aircraft thrust, and blade geometry. Generally, the higher energy levels generated are confined to 1st blade passing frequency (BPF) and its harmonics, while additional broadband components, mainly linked with the blade shape, the developed engine power, and the turbulent boundary layer (TBL), also contribute to the excitation levels. The vibrations problem takes on particular relevance in the case of composite structures. The laminates in fact could exert damping levels generally lower than metallic structures, where the greater amount of bolted joints allow for dissipating more vibration energy. The prediction and reduction of aircraft vibration levels are therefore significant considerations for conventional propeller aircrafts now entering the commercial market as well as for models currently being developed. In the Clean Sky 2 framework, the present study focuses on a practical case inherent to the AIRBUS-Racer program aiming to design and develop a multi-tasking fast rotorcraft. This paper defines a finite elements (FE)-based procedure for the characterization of the vibration levels of a main landing gear (MLG) composite door with respect to the expected operating tonal loads. A parametric assessment was carried out to evaluate the principal modal parameters (transfer functions and respective resonance frequencies, mode shapes, and damping coefficients) of the landing gear-door assembly in order to achieve reduced vibration levels. Based on the FE analysis results, the influence of the extra-damping, location, and number of ballast elements, the boundary conditions were investigated with respect to failure scenarios of the kinematic line opening the study towards aeroelastic evaluations. Further experimental ground test results serve as a validation database for the prediction numerical methods representative of the composite door dynamic response.

Determining Patterns of Distribution of Random Loading Load Cycles in Typical Aircraft Chassis Elements

Abstract: The paper considers the calculation of the estimated probability of the possible occurrence of high loading cycles in the power structures of transport engineering, which can significantly affect their carrying capacity and resource. The latter is caused by the possible occurrence of local deformations of structures, leading to the origin of tired microfractures. The study was conducted on the basis of the analysis of the loads affecting the landing gear of aircraft when driving on the runway and in the process of moving on taxiways in the area of airfields. By processing and analyzing the results of experimental studies, obtained by tensometering of chassis parts of several types of aircraft in the most loaded zones, the law of distribution of maximum variable congestion cycles has been defined alongside with the loads acting on the power parts of transport aircraft in different operating conditions. The parameters of this law are set for the most responsible parts of the aircraft’s chassis, and the probability of rare load cycles of voltage strains above a certain level during the operation of the aircraft is calculated.

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

Abstract: 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.

A Preliminary Assessment of an FBG-Based Hard Landing Monitoring System

Abstract: In aeronautics, hard landing is a critical condition as the aircraft approaches the runway with a vertical velocity that exceeds 2 m/s. Beyond that level, the energy that should be then absorbed by the whole structure could cause severe damage to the landing gear and the whole structural system. This document reports on the set-up, execution and results of a preparatory test campaign performed on a small landing gear (LG) demonstrator instrumented with a fibre-optic sensor system. In detail, a leaf spring landing gear was released from a drop tower to detect information about the strain state and the related acceleration history of some specific components during the impact. The objective of the present research is the development of a method for assessing whether hard landing is experienced, and to what extent. Deformation measurements through an integrated Fibre-Bragg Grating (FBG) network allowed retrieving impact velocity by a devoted, original algorithm. The proposed preliminary methodology is the base for assessing a more complex procedure to correlate structural response to the energy entering the structure during the touchdown event.

Design and Manufacture of Composite Landing Gear for a Light Unmanned Aerial Vehicle

Abstract: Unmanned aerial vehicles (UAVs) have become popular for military applications as well as for use in structural inspection, weather monitoring, and festival demonstrations. Suitable landing gears to ensure that the UAV can take off and land safely are important when the price of the cargo and UAV increase. A lightweight and high-strength landing gear is desirable to overcome accidents during service. Composite materials are a promising, excellent solution for this purpose. This study demonstrated the design, numerical analysis (Ansys), manufacture, and experimental verification (LabVIEW) of a composite landing gear for a UAV. In particular, landing gears with different carbon fiber-reinforced polymer (CFRP) composite fiber orientations were analyzed, manufactured, and experimentally verified in this study.

A Rational Numerical Method for Simulation of Drop-Impact Dynamics of Oleo-Pneumatic Landing Gear

Abstract: Oleo-pneumatic landing gear is a complex mechanical system conceived to efficiently absorb and dissipate an aircraft’s kinetic energy at touchdown, thus reducing the impact load and acceleration transmitted to the airframe. Due to its significant influence on ground loads, this system is generally designed in parallel with the main structural components of the aircraft, such as the fuselage and wings. Robust numerical models for simulating landing gear impact dynamics are essential from the preliminary design stage in order to properly assess aircraft configuration and structural arrangements. Finite element (FE) analysis is a viable solution for supporting the design. However, regarding the oleo-pneumatic struts, FE-based simulation may become unpractical, since detailed models are required to obtain reliable results. Moreover, FE models could not be very versatile for accommodating the many design updates that usually occur at the beginning of the landing gear project or during the layout optimization process. In this work, a numerical method for simulating oleo-pneumatic landing gear drop dynamics is presented. To effectively support both the preliminary and advanced design of landing gear units, the proposed simulation approach rationally balances the level of sophistication of the adopted model with the need for accurate results. Although based on a formulation assuming only four state variables for the description of landing gear dynamics, the approach successfully accounts for all the relevant forces that arise during the drop and their influence on landing gear motion. A set of intercommunicating routines was implemented in MATLAB® environment to integrate the dynamic impact equations, starting from user-defined initial conditions and general parameters related to the geometric and structural configuration of the landing gear. The tool was then used to simulate a drop test of a reference landing gear, and the obtained results were successfully validated against available experimental data.

Effect of Fillet Radius of UAV Main Landing Gear on Static Stress and Fatigue Life using Finite Element Method

Abstract: The landing gear is one crucial component in the UAV aircraft structure because it serves as the main supporting component of aircraft load when landing and take-off. This study aims to determine the effect of the fillet radius on static stress and fatigue life of the main landing gear for UAV aircraft. Static stress and fatigue life analysis using the finite element method with Ansys Workbench software. The fillet radius is varied 120, 130, 140, and 150 mm. Predictions for fatigue life use the Gerber mean stress theory with a full-reserved type of loading. Landing gear material uses Aluminium alloy 6061. The static stress analysis shows that the higher the fillet radius, the higher the von Mises stress of the main landing gear frame. The fatigue life analysis shows that the higher the fillet radius, the lower the fatigue life of the main landing gear frame. The main landing gear frame achieves the highest fatigue life of up to 3.90 x 107 cycles at a fillet radius of 120 mm.

Comprehensive design of an oleo-pneumatic nose landing gear strut:

Abstract: A comprehensive design cycle of a nose landing gear strut having an oleo-pneumatic shock absorber for a lightweight aircraft is proposed. Design and analysis of a retractable nose landing gear acco...

Helicopter Shipboard Landing Simulation Including Wind, Deck Motion and Dynamic Ground Effect

Abstract: A first principles physics-based simulation framework that accounts for wind-over-deck (WOD) and ground effects during approach and landing of a helicopter on a ship deck is developed. The WOD velo...

Two-parameter bifurcation analysis of an aircraft nose landing gear model

Abstract: The Hopf–Hopf bifurcations of an aircraft nose landing gear model are investigated in this paper based on two pairs of continuation parameters. It is shown that due to the effect of higher-order terms, there exists a deviation between the bifurcation curve of the original system and the bifurcation curve of its truncated amplitude system, which results in a contraction in the bistable region compared with the previous work. Two codimension 3 strong resonant points can be detected on the Neimark–Sacker bifurcation curve. Period-3 and period-4 limit cycles with torsional-lateral shimmy can emerge when the vertical force and the taxiing velocity are chosen near the resonant points. The occurrence of 1:3 and 1:4 resonant Hopf–Hopf bifurcations can induce tire-ground vibrations in torsional and lateral direction, which can greatly degrade the performance and safety and possibly destroy the airstrip. So it is of significance to investigate the resonate behaviors of the aircraft nose landing gear to ensure the safe landing.

Application of Operational Load Monitoring System for Fatigue Estimation of Main Landing Gear Attachment Frame of an Aircraft.

Abstract: In this paper, we present an approach to fatigue estimation of a Main Landing Gear (MLG) attachment frame due to vertical landing forces based on Operational Loads Monitoring (OLM) system records. In particular, the impact of different phases of landing and on ground operations and fatigue wear of the MLG frame is analyzed. The main functionality of the developed OLM system is the individual assessment of fatigue of the main landing gear node structure for Su-22UM3K aircraft due to standard and Touch-And-Go (T&G) landings. Furthermore, the system allows for assessment of stress cumulation in the main landing gear node structure during touchdown and allows for detection of hard landings. Determination of selected stages of flight, classification of different types of load cycles of the structure recorded by strain gauge sensors during standard full stop landings and taxiing are also implemented in the developed system. Based on those capabilities, it is possible to monitor and compare equivalents of landing fatigue wear between airplanes and landing fatigue wear across all flights of a given airplane, which can be incorporated into fleet management paradigms for the purpose of optimal maintenance of aircraft. In this article, a detailed description of the system and algorithms used for landing gear node fatigue assessment is provided, and the results obtained during the 3-year period of system operation for the fleet of six aircraft are delivered and discussed.

Evaluation of Unmanned Aircraft Flying/Handling Qualities Using a Stitched Learjet Model

Abstract: Over the past 20 years, unmanned aircraft have taken over military missions that were deemed to be too “dull, dirty, or dangerous” for manned aircraft. The urgent demand for aircraft that can execu...

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

Abstract: 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.

Generative design case study of a CNC machined nose landing gear for an unmanned aerial vehicle

Abstract: Generative design is a design method inspired by nature’s evolution, pushing the limits of the industry to new design solutions. Using minimum input requirements, the resulting designs can be structurally adequate, weight-optimised and almost production-ready. The main purpose of this paper is to present the different approaches of the standard engineering design and the generative design methods. This is achieved through the case study of a nose landing gear for a prototype tactical unmanned aerial vehicle, intended for low volume production. The first part of the paper outlines the conceptual design of the nose landing gear. Subsequently, during the preliminary phase, the stress distribution along the different parts is calculated, based on the classic Strength of Materials theory and therefore a design solution is produced. In the second part, a generative design study is carried out with a commercially available tool, based on the conceptual parameters previously chosen. Both concepts are studied with industry-standard finite element analysis tools in order to validate, from a theoretical standpoint, the strength requirements according to the STANAG 4671 regulation. The final structure will be manufactured with 3-axis CNC machining, while providing about 36% weight reduction without compromising the structural functionality.

A Test Method for Helicopter Landing Gear Load

Abstract: In this paper, a load test method of landing gear during take-off and landing of helicopter was proposed and the structure of helicopter landing gear, the modification of strain gauge bridge, the establishment of load calibration equation and the flight test of helicopter were studied. Firstly, according to the structure of helicopter landing gear, the stress analysis of landing gear was carried out, and the load position and force form of landing gear were determined during take-off and landing. Then, the measuring principle of the strain bridge was studied. According to the technical requirements, structural characteristics of the landing gear load test and the properties and principles of the strain bridge, the distribution and load measurement form of the strain bridge of the dangerous structure of the landing gear were designed. Then, studying load calibration test scheme of landing gear and carrying out load calibration test, the load calibration equation of landing gear was obtained, and the accuracy of load calibration equation was verified by comparing the expected load and actual load. Through the flight test, the landing gear load during the take-off and landing of the helicopter was obtained. Finally, the valid analysis of flight load data was carried out. The results show that the proposed method is feasible, and the flight test data of landing gear load are accurate and reliable, which can provide data support for the structure modification, fatigue analysis and the life evaluation of landing gear.

Effect of Bolt Hole Size on Static Stress and Fatigue Life of UAV Main Landing Gear Using Numerical Simulation

Abstract: Currently, the use of Unmanned Aerial Vehicle (UAV) or Drone for various applications in science and engineering has increased significantly. One of the essential components of a UAV aircraft is the landing gear which plays an important role during take-off and landing. The paper research the effect of the bolt hole size on the static stress and fatigue life of main landing gear in the UAV aircraft using numerical simulation with Ansys Workbench. The bolt hole size varies 8, 9, 10, 11, and 12 mm. Gerber mean stress theory with a full-reserved type of loading is used to predict the fatigue life. The static stress simulation results show that the higher the bolt hole size, the higher the von Mises stress of the main landing gear frame. The fatigue life analysis shows that the higher the bolt hole size, the lower the fatigue life of the main landing gear frame. The main landing gear frame fails to achieve a minimum fatigue life of 1 million cycles at a 12 mm bolt hole size.