Main Landing Gear Research Articles

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

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.

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

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.

Vibration Characteristics of Unsaturated Runways Under Moving Aircraft Loads

The dynamic vibrations of airport runways induced by moving aircraft loads are semi-analytically studied in this paper. The airport runway consists of an infinite Kirchhoff plate, an elastic base course, and an unsaturated poroelastic half-space. The aircraft loads are modeled according to the mechanical properties of the main landing gear of the A380 civil airliner. The governing equations of the whole system are solved in the wavenumber domain using the double Fourier transform. Then the results in the spatial domain are obtained by applying the inverse double Fourier transform. Various parameters including the observation location, soil saturation, load speed, load frequency, and pavement rigidity on the vibration characters of the whole system are investigated. It is found that all these effects are crucial, and the increase of soil saturation leads to a larger maximum vertical displacement and lower critical speed.

DESIGN OF FORCE MEASURING SYSTEM ON MAIN LANDING GEAR WEIGHT DROP TESTING MACHINE FOR THE APPLICATION OF LSU SERIES

In this research, the design of the force measuring system on main landing gear weight drop test for the LSU series that developed by LAPAN was carried out. The principle of this machine is to apply the load according to the weight of the aircraft on the main landing gear and drop it at a certain height assisted by the guiding rail. At the bottom of this machine there is a impact platform where each angle is mounted with a load cell that functions to measure the reaction force due to the impact of the main landing gear. In addition, there is a data acquisition system whose function is to process the output signal from load cell and display measurement data. The data acquisition system used consists of DAQ measurement hardware made by national instruments and LabVIEW software installed on a PC. The design of this testing tools aims to carry out a dynamic impact test on the main landing gear structure of the UAV. In this study, static calibration has also been successfully performed on the impact platform and shows consistent results for various test masses.

Detection of Aircraft Touchdown Using Longitudinal Acceleration and Continuous Wavelet Transformation.

The paper presents a methodology enabling the detection of aircraft touchdowns based on data obtained from accelerometers attached to the structural parts of the airframe in the cockpit or passenger compartment. Precise determination of the moment and place of touchdown of the main landing gear is challenging when analysing parameters such as height, flight speed and rate of descent. During the tests of the I-31T aircraft, it turned out that vibrations of the aircraft structure caused by the contact of the front and main landing gear with the ground have a repetitive character. In particular, this applies to longitudinal acceleration. The use of continuous wavelet analysis (CWT) allowed finding unique periodic features of the landing phenomenon that distinguish it from other forms of vibration occurring in individual flight phases. Ground and flight observations of experimental aeroplane MP-02 Czajka verified the proposed method of virtual touchdown detection. The results presented in this paper justify that this method may find broader application, especially for the light aircraft class.

Preliminary calculation of the landing gear of a military training aircraft

The paper presents a preliminary calculation method, which is easy to apply for pre-dimensioning the landing gear. Preliminary calculation of the landing gear includes estimating the loads on landing and determining the position of the nose landing gear and the main landing gear of a military training aircraft. Another purpose of the preliminary calculation is to ensure the stability of a military training aircraft on landing and take-off, as well as to ensure the lateral stability of the aircraft during ground operations such as taxiing, landing or take-off.

Three-dimensional visualization of flow pattern near transport airplane model with operating propellers in wind tunnel

This paper presents the experiment results of three-dimensional visualization of flow pattern behind the wing and fuselage of the light transport aircraft (LTA) model with operating propellers in the T-102 TsAGI subsonic wind tunnel (WT). Studying the flow pattern, it is possible to recognize the features of the flow and aerodynamic interference of model elements. As a result of the analysis of the flow pattern and comparison with the previously obtained integral characteristics, the model elements for improving the aerodynamic perfection of the aircraft are revealed. It is shown that at operational angles of attack behind the main landing gear fairing, the vortex flow forms, increasing drag and, apparently, negatively affecting the longitudinal stability characteristics. Vortices are formed behind the flattened tail of the fuselage. Thus, the visualization of the flow with dacron ribbons is an effective method of obtaining flow pattern around the airplane model elements in WT.

민감도 분석을 통한 항공기 주 착륙장치 미접힘 결함에 미치는 주요 조인트 유격의 영향 연구

항공기 주 착륙장치가 접히지 않는 결함이 발생하였다. 결함의 직접 원인은 비정상적인 밸브 입력이고, 근본 원인은 주 착륙장치 조인트에 존재하는 유격의 누적으로 추정된다. 주 착륙장치는 하나의 유압 작동기와 여러 링크의 조립체이다. 결함에 미치는 영향이 큰 조인트를 식별하기 위해 주 착륙장치의 기구학 모델에 기반한 민감도 분석을 실시하였다. 모델에서 각 링크를 강체로 가정하였으며, 상대적인 위치는 기하학적으로 결정하였다. 민감도 분석 전 기술 도서 상의 데이터를 이용하여 모델을 교정하였다. 교정된 모델과 실험 계획에 기반하여 컴퓨터 실험을 실시하였다. 그 결과 비정상 작동을 일으키는 상대적으로 유력한 조인트를 찾을 수 있었다. 모델의 타당성 검증은 실제 결함 데이터를 활용하여 수행하였다.

Power Drive Electronics Reliability in More Electric Aircraft

This paper presents an ‘Integrated Reliability Paradigm’ for a composite reliability assessment of power devices and the power systems they build, when arranged in networks, for power conversion, inversion, and switching functions. Especially, in times when the traditional aircraft architecture is transforming into more electric aircraft (MEA) configuration, the need for an integrated approach that evaluates the reliability from device up to the system level has become all-important. The proposed integrated reliability paradigm realizes this need by devising an efficient framework that provides tools for modelling and evaluating the reliability of power drive electronics to ensure highly dependable power systems/sub-systems onboard MEA. The paradigm is validated on an electro-mechanical actuator (EMA) of the electric braking sub-system of the main landing gear.

Wind-tunnel and CFD investigations of UAV landing gears and turrets – Improvements in empirical drag estimation

This paper analyzes the drag characteristics of several landing gear and turret configurations that are representative of unmanned aircraft tricycle landing gears and sensor turrets. A variety of these components were constructed via 3D-printing and analyzed in a wind-tunnel measurement campaign. Both turrets and landing gears were attached to a modular fuselage that supported both isolated components and multiple components at a time. Selected cases were numerically investigated with a Reynolds-averaged Navier-Stokes approach that showed good accuracy when compared to wind-tunnel data. The drag of main gear struts could be significantly reduced via streamlining their cross-sectional shape and keeping load carrying capabilities similar. The attachment of wheels introduced interference effects that increased strut drag moderately but significantly increased wheel drag compared to isolated cases. Very similar behavior was identified for front landing gears. The drag of an electro-optical and infrared sensor turret was found to be much higher than compared to available data of a clean hemisphere-cylinder combination. This turret drag was merely influenced by geometrical features like sensor surfaces and the rotational mechanism. The new data of this study is used to develop simple drag estimation recommendations for main and front landing gear struts and wheels as well as sensor turrets. These recommendations take geometrical considerations and interference effects into account.

Mechanism analysis of a main landing gear of transporting aircraft: A design learning perspective

The landing gear lifetime is estimated based on the safe-life design concept and its design requires thorough calculations. The individual parts and sub-assemblies must be sensibly designed to function safely and efficiently for the specified design lifetime without failure. In a design process of a main landing gear system, the kinematics/mechanisms analysis shall be first carried out as a primary task for feasibility of the gear retraction/extension with the satisfactory link paths. This paper presents the analytical kinematics analysis of a complex mechanism involving multiple four-bar linkages with multiple coupler points of the main landing gear (MLG) of CN-235 aircraft. The kinematics analyses were performed in order to figure out the overall link positions of the main landing gear mechanism and make scenarios of a deformed component from its designed geometry for possibilities of a lock failed position.

Review Facility Development of Aircraft Tire Retreading in Indonesia

Aircraft tire retread is the process of retreading or reconditioning aircraft tires after being used several times for take off and landing. Retreading an aircraft tire can be done many times, which is between 3-5 times depending on the level of wear of the tire layer. Data from INACA ‘Indonesia AviationOutlook 2017’ shows that the number of jet aircraft owned by Indonesian airlines for Wide Body is 23 aircraft and Narrow Body is 338 aircraft. Where the number of aircraft tyre in the Nose Landing Gear / NLG and Main Landing Gear / MLG Wide Body aircraft are 55 EA and 216 EA respectively, while for Narrow Body aircraft each is 352 EA and 1488 EA. The available information states that tire retreading needs in Indonesia are around USD 20 million per year. There is a huge opportunity in the need for retreading aircraft tires owned by Indonesian airlines, which is around USD 20 million per year, with 10% growth per year, so the next 5 years will reach around USD 30 million. However, this opportunity cannot be taken by MRO Indonesia because MRO Indonesia does not have the ability to retread airplane tires. The cause of the inability to take up an aircraft tire retreading business opportunity is partly because there is no government policy support to encourage aircraft tire manufacturers to collaborate with Indonesian investors to build a tire retread facility, there is business competition with aircraft tire retreading in Malaysia and Thailand, businesses most only think solely of big profits, and the unattractive business climate in Indonesia such as complicated licensing, inefficient supply chains and incentives provided are less attractive. The steps needed to capture the opportunity to retread aircraft tires are to carry out continuous campaigns and incorporate aircraft tire retread facilities development programs into the National Strategic Program and the Aerospace Industry Roadmap.

Landing efficiency control of a six degrees of freedom aircraft model with magneto-rheological dampers: Part 2—control simulation

In Part 1 of this work, both the kinematic and dynamic equations of aircraft landing model integrated with magneto-rheological damper were derived. In Part 2, the landing efficiency is analyzed through landing motion simulation which is performed on the basis of the model equations derived in Part 1. To investigate the landing efficiency with respect to the operating force control of magneto-rheological fluid, two different control logics for magneto-rheological damper are designed. The first one is the skyhook controller, which is known to be simple, but very effective for the semi-active control system. In this control logic, the switching condition depending on the compression and extension mode of the damper is determined to achieve maximum energy dissipation. The second one is a modified skyhook controller associated with the semi-active bouncing control. This controller is introduced to prevent bouncing of the main landing gear tires and to reduce the roll motion of the aircraft. The landing efficiency is evaluated at several rates of descent, and its distinct features such as tire displacement and pitch angle are compared in the time domain.

Complex composite technology investigation: simulations and experimental results

The paper deals with discussion of research activities within ITEMB (InTEgrated Full Composite Main landing gear Bay Concept) framework, an EU Clean Sky 2 program coordinated by Airbus. The driving motivation for the investigation on such a technology was found in the opportunity to design a main landing gear bay in a full composite configuration: rational approaches have been implemented in an efficient testing stage providing the necessary database for the static qualification of the conceived design. Advanced and innovative solutions for a “more integrated” system were duly analysed and experimentally validated thus proving the overall device compliance with industrial standards and applicable airworthiness requirements.

Development of a Morphing Landing Gear Composite Door for High Speed Compound Rotorcraft

In the framework of fast rotorcraft, smoothness and flushness of external aerodynamic surfaces present challenges for high-speed conditions, where aerodynamics is the driver of helicopter performance. For AIRBUS-RACER helicopter the main landing gear trap doors are parts of the lower wing skins (in retracted configuration) affecting helicopter performance by minimizing the drag. Flushness requirements must not be in contrast with the functionally of the Landing gear system that must open and close the doors during the landing gear retraction-extension phases at moderately low velocity. To manage these goals, a novel design logic has been identified to support the trap doors development phase. The identified way to proceed needs of relevant numerical method and tool as well. This method is aimed at identifying the main landing gear composite compartment doors in pre-shaped configuration to match the smoothness and door-stopper engagements over each aerodynamic conditions. The authors propose a detailed non-linear Finite Element method, based on MSC Nastran (MSC Software, Newport Beach, US) SOL-400 solver in which the structure is modelled with deformable contact bodies in a multiple load step sequence, open door condition and pre-shaped, deformed under actuator pre-load, under flight load conditions. The method includes the entire pre-stressed field due to the preload and the actual door stiffness, considering the achieved large displacement to verify the most representative strain field during loads application. The paper defines a robust methodology to predict the deformation and ensure the most appropriate door “pre-bow” and pre-load, in order to achieve the desiderated structural shape that matches aerodynamic requirements. The main result is the identification of a pre-shaped doors configuration for the Airbus RACER Fast Rotorcraft.

Determinant assembly approach for flat-shaped airframe components

The optimization of the aeronautical structure manufacturing is a challenging task in the development of a new aircraft. To date, aeronautical industries are funding research about new assembly approaches based on cost reduction and increased efficiency of the assembly processes. The work here presented focused on an innovative assembly method based on the integration between statistical methods of tolerance prediction and the determinant assembly approach. The coupling tolerances between airframe components are predicted through statistical approach in order to reduce the features manufactured in assembly. This aspect contributes to a reduction of the costs due non-recurring costs. The method proposed has been tested on a dedicated case study developed in the frame of the “integrated main landing gear box” project on the CleanSky2 Research program. Tests have been conducted to check the consistency of the method and its feasibility in the industrial contexts in the case of flat-shaped component. The performed experiments confirmed the analytical study.

Computational Evaluation of Aerodynamic Loading on Retractable Landing-Gears

Computational fluid dynamics is employed to evaluate the mean aerodynamic loading on the retractable landing-gears of a regional transport commercial aircraft. The mean turbulent flow around simplified landing-gear systems including doors is simulated by using the Reynolds-averaged Navier–Stokes approach, where the governing equations are solved with a finite volume-based numerical method. Using a dynamic meshing method, the computational grid is automatically and continuously adapted to the time-changing geometry, while following the extension/retraction of the landing-gear systems. The temporal evolution of the aerodynamic forces on both the nose and the main landing-gears, along with the hinge moments of the doors, is numerically predicted. The proposed computational modeling approach is verified to have good practical potential when compared with reference experimental data provided by the Leonardo Aircraft structural loads group.

Fault Analysis of Abnormal Opening of the Main Landing Gear Door of Civil Aircraft

The main landing gear door is an important component of the landing gear system. The system is in a state of failure and will not play the role of extending and retracting when the door extension/retraction fault. This article analyzes the main landing gear door extension/retraction principle and fault cause of civil aircraft, deeply studies the control process and logic of the Uplock, and improves the understanding of the landing gear door extension/retraction system.

Numerical Study Via Finite Element Analysis of the Structural Behavior of Rigid Pavement of Aerodromes

The present study develops a 3D numerical model of the concrete pavement system of aerodromes in contact with the main landing gear of aircrafts using Finite Element Method (FEM). The pavement system used in the analysis consisted of six concrete slabs overlaying a subgrade medium with stiffness k. Doweled bars are considered for the pavement transverse joints while aggregate interlocks are considered for longitudinal joints. A parametric study was conducted to validate the model numerically, as well as to investigate the influence of the doweled bars, aggregate interlocks and subgrade stiffness on the pavement deflections when it is subjected to a dynamic load. About 77% decrease in deflection was attained due to the presence of doweled bars. This study additionally presents a methodology for designing the pavement thickness and the compressive strength of concrete based upon the Mohr-Coulomb’s failure criterion. It is found that for a pavement thickness of 0.305m the minimum compressive strength of concrete should be 28 MPa.

Design and prototyping of a novel composite architecture for a widebody landing gear bay

Composite materials may reduce the final weight of the aircraft structural components, in addition to improve fatigue performance and corrosion resistance. In order to achieve the optimization of air transport systems, making them increasingly sustainable, the structural design must be surely reviewed, starting to follow the “composite thinking” philosophy. The present research provides some relevant outcomes concerning the design of a composite sample for the main landing gear bay of a large commercial airplane (EASA CS25 category), within ITEMB (InTEgrated Full Composite Main landing gear Bay Concept) project, a program of Clean Sky 2 EU research framework. The most ambitious goal is to develop a new generation of Lower Center Fuselage (LCF) with an innovative integrated landing system in the fuselage, which is considered the next frontier in the development of landing systems for medium-haul aircraft, such as the Airbus A320 aircraft family. The development of a different architecture, with the landing gear integrated within the related fuselage bay, could lead to a simplification of the whole sub-assembly with potential advantage in terms of construction and assembly times. Final target of the project is the manufacturing of an innovative monolithic composite structure that will replace the actual configuration (a mixed structure of metal and composite sub-assemblies) reducing or actually removing all the cost of assembly and increasing the production rate. This paper presents the main results of the work, introducing the main processing steps and prototype results; in the last part of the work, also some experimental test on significant element are introduced as first assessment of the technology readiness level that has been achieved.