Advanced Technology Helicopter Landing Gear.

The Weight on Wheel system on an aircraft gives an indication of whether the aircraft has weight on its wheels, meaning the airborne is on the ground. This system monitors the loads appearing on each Landing Gear structure. It sends a status signal to Landing gear computer that manage the redundant signals coming from each WOW systems. The management of these signals gives the information needed to activate “on ground” configuration of aircraft for braking control laws. “On ground” configuration specifies maximum load conditions and requirements for shock absorbers design for each type of aircraft (heavy freighters, military transport …) Based on CESA experience on this field, a new approach oriented to fatigue health monitoring, is presented here. Current WOW system could be modified allowing a continuous monitoring of loads experienced by Landing Gear structure. This will optimize the life cycle of the aircraft by checking individually the status of different structural parts of each Landing Gear. Therefore, it will improve maintenance actions that will be performed only when needed. Load detection and monitoring of landing gears provides a valuable and useful information data to predict accurately the accumulated fatigue damage on landing gear components.

In this chapter, first, basic information about the landing gear (definition, purpose, and duties, etc.) is given. Examples of different aircraft are given throughout the chapter. Systems in large aircraft such as extend-retract mechanisms are explained on Boeing 737 aircraft. As mentioned in the chapter introduction, landing gears are the elements that provide contact with the ground during the landing—takeoff phases and movements on the ground (during taxi), the friction resistance is minimized, and they best absorb the loads caused by the horizontal and vertical movements of the aircraft. Afterward, different landing gear layouts and their usage areas, advantages, and disadvantages are mentioned. Landing gear struts, which are one of the basic elements of the landing gear and provide structural strength, are mentioned. By specifying the characteristics of different strut structures, the damping structure of the energies arising from the landing is explained. After the strut structures, wheels, tires, and brake structures, which are the other basic elements of the landing gear, are explained. Since there are retractable landing gears in large aircraft, the extend-retract mechanisms of the main and nose landing gear, their controls, and indicators are mentioned. Finally, the nose wheel steering mechanism that provides guidance during movement on the ground and the tail skid structure that prevents the tail from hitting the ground directly during takeoff are mentioned.KeywordsLanding gearMain landing gearNose landing gearExtend-retract mechanismAeronautics

Flyover noise of modern aircraft in their approach configuration can be dominated by airframe noise. Relevant flow noise sources are high lift devices and landing gears. Therefore aeroacoustic tests were performed in the German Dutch Wind Tunnel employing full-scale landing gears of an A340 aircraft. Farfield noise characteristics were determined for both a nose- and a main landing gear, the latter in a 4-wheel and a 6-wheel mock-up configuration, at wind speeds ranging from 50 to 78 m/s. DNW's 3m acoustic mirror and a planar microphone array served for source localization and ranking. Excess tone noise was detected and originated from pin-cavities. Broadband noise levels were confirmed to increase with the 6th power of flow velocity. Noise directivities feature weak level maxima both in the forward and rear arc. Based on results from earlier testing on a smaller A320 gear the effects on noise of gear size and configuration were evaluated. By covering different gear components with streamlined fairings an overall noise reduction on the order of 3 dB was achieved.

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.

This study investigates the substantial challenges that landing gear systems face due to increased aircraft speeds and traffic volumes, focusing particularly on bird strike incidents. By utilizing the Smoothed Particle Hydrodynamics (SPH) method alongside a rigid-flexible coupling finite element model, we analyzed the dynamic characteristics of bird impacts on ten typical landing gear structures. The simulations indicated that stress peaks exceeding 1200 MPa occurred in the nose landing gear pipelines, drag brace, spring, and main landing gear pipelines post-impact, leading to severe damage and loss of functionality. The aluminum drag brace displayed deformations greater than 15 mm, which poses significant safety risks. Additionally, a positive correlation was observed between peak structural deformation and bird impact speed on the main landing gear’s upper locking rod, with larger deformations inducing significant concentrated stress in the pin joints, which escalates with increased speed. Structures not directly impacted by the bird strike maintained sufficient rigidity, though certain critical areas require enhanced strength and protective measures such as reinforced panels in the design. This research provides theoretical support for designing bird strike protection in landing gear systems.

In this paper we are presenting a manufacturing method for a main landing gear of an aerial target. We approached the stages of manufacturing of a main landing gear from composite materials dedicated for an aerial targeted plane. In the first stage we designed a reduced mass landing gear by using CAD/CAM simulation and design (Solids Works).In the second stage we realised the manufacturing technologyto create the CAD model at a reduced cost. For this, we designed and manufactured the mould of composite preform and the mathematic model where we configured the mass and dimensonal parameters for the main landing gear. We verified this mathematical model by comparing the mass and dimensional parameters theoretically obtained with the practical ones for more manufactured landing gears.

In earlier publications of landing gear shimmy analysis, efforts have concentrated on predicting the onset of shimmy instability and investigating how to stabilise shimmy-prone landing gears. Less attention has been given to the improvements of shimmy performance for a gear that is free from dynamic instability. This is the main interest of this work. We investigate the effectiveness of a linear passive mechanical device that consists of springs, dampers and inerters on suppressing landing gear shimmy oscillations. A linear model of a Fokker 100 main landing gear and two configurations of candidate shimmy suppression device have been presented. Considering the physical shimmy motions, time-domain optimisation of the parameters in the shimmy suppression devices, using a cost function of maximum amplitude of gear torsional-yaw motion, has been carried out. The performance advantage of a shimmy suppression device incorporating inerter has been presented.

Structural design concepts for load bearing mechanical systems vary due to individual usage requirements. Particularly strut-configurations for landing gears in airplanes push the envelope according to tight requirements in shock absorption, normal, lateral and torsional load capacity, rolling stability, storage dimensions, low drag, low weight, and maintenance as well as reliability, safety and availability. Since the first controlled and powered flight of the Wright-Brothers in 1903, design evolution generated different structural design concepts. Today’s structures may have, seemingly, reached mature conformity with distinct load path architectures that have been prevailed. In the proposed contribution, the authors evaluate and compare distinctive performance requirements like stroke ability and ride quality, elastic force retention, structure strength, and weight of mechanisms resulting from significant structural design concepts for main and nose landing gears. Loads in landing gears have always been distributed in struts with high and low amounts of strut members such as rods, beams, torque links, and joints as well as different types of absorbers. This paper’s goal is to clarify pros and cons of the four different concepts with respect to their vulnerability due to uncertainty. Here, uncertainty mainly occurs due to variations in elastic force retention and their effect on the performance requirements. For that, simple mathematical models are derived to evaluate and compare the most significant characteristics of the four concepts in the earliest stage of development in order to make early decisions for or against a concept before time and cost consuming detailed development work including manufacturing and test takes over.

The landing gear is one crucial component in an Unmanned Aerial Vehicle (UAV) aircraft construction. Landing gear serves as the main supporting component of aircraft load when landing and take off. This research aims to investigate the fatigue design life of the main landing gear on the UAV aircraft. The main landing gear frame design used Autodesk Inventor Professional 2017, while finite element analysis used Ansys Workbench software. It is subjected to a load of 1500 N with a loading fully-reserved. The prediction for fatigue life using Gerber mean stress theory. The material of the main landing gear frame is Aluminum alloy 6061. The simulation results show that the main landing gear frame has a minimum fatigue life of up to 3.5 x 10 7 cycles with a minimum safety factor of 1.43.

A simple method of investigating the effect of joint clearances on landing gear retraction failure is presented and applied to the main landing gear with a single sidestay and a hydraulic actuator. A geometric model is presented with assumptions of each link as a rigid body and their relative positions geometrically determined by considering the size of the clearances. We conducted a sensitivity analysis based on a geometric model of the main landing gear. The model was calibrated using the data from the technical order. A Monte Carlo simulation (MCS) was conducted, and whose input was the distance of each clearance based on the experimental design that combined the modified Latin hypercube sampling (LHS) and central composite design (CCD). As a result, we were able to find that the joint had a high potential to operate abnormally. We validated the model by using the actual failure data. Finally, the physical meaning of the sensitivity analysis results was interpreted by comparing them with the values obtained through an amplification index method that is a modified linearization method.

This paper highlights the effectiveness of noise-reduction devices on an 8%-scale, detailed four-wheel main landing gear model based on NASA’s design for the high-lift common research model (CRM-HL). This project is a collaborative effort between JAXA and Safran Landing Systems to reduce landing gear noise from commercial airplanes. The study investigates three types of noise-reduction devices that utilize porous plates: a truck beam porous plate with forward-bent edges, main strut porous plates, and brace porous plates. Although the main landing gear is a generic research model, the noise-reduction devices were designed to be structurally practical while considering the landing gear’s retractability and clearance margins. Far-field noise measurements were conducted at a freestream wind speed of 80 m/s on the stand-alone main landing gear model, both with and without noise-reduction devices. Additionally, computational simulations were performed to validate results against experimental data and to enhance understanding of the noise-reduction effects by visualizing flowfields. The noise-reduction configuration using the three devices significantly reduced noise by over 2 dB at all four microphone locations in a wind-tunnel test.

The main landing gears of large commercial aircraft are an important contributor to the total aircraft noise during landing approach. Within a European financed research project called SILENCER (“Significantly Lower Community Exposure to Aircraft Noise”) a study in “advanced low noise landing gear design” was performed to develop operational landing gears that take into account aeroacoustic constraints early in the design stage. In full scale tests a good level of noise reductions was achieved relative to the equivalent conventional landing gears. For the main landing gear however, there was evidence that further noise reductions might be achievable by refining the design of the bogie. This paper describes a follow- on study at 0.25 model scale to investigate in detail some of the design parameters that affect the noise of the bogie. The test results show that the distribution of sources on the bogie is sensitive to the detailed design, but that achieving reductions in total noise is not straightforward. Analysis of flow patterns indicated by the noise data and flow visualization does however lead to a number of ways of adapting the design of the gear to provide significant noise control.

Investigation of gear walk suppression while maintaining braking performance in a main landing gear

The main landing gear is one of the important components in UAV aircraft. This paper aims to analyze the natural frequency of the main landing gear and determine its normal mode shape. This analysis is important so that no resonance causes damage to the main landing gear components. The main landing gear uses Aluminum 6061 material and the analysis is carried out using the finite element method with the help of Ansys Workbench software. The analysis showed that the natural main landing gear frequencies for mode 1 to mode 6 were 76.04 Hz, 85.07 Hz, 167.82 Hz, 201.92 Hz, 288.39 Hz, and 327.00 Hz, respectively. The maximum deformation of the main landing gear for mode 1 to mode 6 is 33.73 mm, 35.35 mm, 48.16 mm, 44.62 mm, 38.14 mm, and 41.51 mm, respectively.

The design of the nose landing gear (NLG) torsional damping is very important to avoid the taxiing vibration of the aircraft. On the one hand, increasing the torsional damping can suppress the nose wheel shimmy. On the other hand, if the design value is too large, it will cause unstable vibration of the aircraft direction, and the latter will often be ignored, which will bring potential risks to the taxiing safety of the aircraft. In this paper, by establishing a multibody dynamics model (MBD) of aircraft taxiing, including NLG, main landing gear (MLG), airframe, related force elements and kinematic pairs, the effect of the torsional damping of NLG on aircraft directional stability is studied, and the key taxiing parameters of aircraft taxiing in an unstable direction are obtained. In order to propose the damping design specification for the nose landing gear anti-shimmy system, the critical value of torsional damping for stable taxiing in the direction of the aircraft is calculated. It is found that nose wheel shimmy and the unstable vibration of the aircraft direction will occur simultaneously, but the vibration frequencies are different. Therefore, in addition to the anti-shimmy design, the influence of the aircraft’s directional unstable vibration must also be considered in the engineering application.