Landing Gear Systems in Aircraft

Electrical linear actuators reduce the weight of landing gear retraction / extension mechanism which helps in keeping the gross takeoff weight of aircraft weight low. Reduction in weight of the aircraft has manifold advantages in which noticeable are increased endurance, range, climb performance, acceleration performance and fuel efficiency. Use an electrical linear actuator in landing gear system is a simplification in the kinematics of landing gear retraction / extension sequence. In this research, a retraction / extension mechanism for nose landing gear (NLG) of a MALE UAV has been designed and tested according to FAR CFR 25.729. The design process of a Retractable Landing Gear System Mechanism (RLGS) started with selection of pivot point on NLG and axis for the rotation in free space available which resulted in least power requirement. Pivot point was selected such that no part of gear posed hindrance to other part of an aircraft. Next, the path of rotation about pivoting axis and position kinematics were calculated using vector loop closure equation. Essential parameters regarding retraction / extension sequence were calculated from trigonometry. Forces and power required for complete retraction / extraction sequence were calculated. During the research, it was found that retraction force on NLG depended upon the aerodynamic drag, inertial loads and gravitational force. In this research analysis of these forces is presented with much detail. Effect of velocity variation of linear actuator on the retraction force is commented upon. Computational analysis is carried out using multibody dynamics MSC ADAMS® software. The research concluded with experimental validation of a planner triangular retraction mechanism of NLG actuated by electrical linear actuator.

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.

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 system is the dominant airframe noise source for most modern commercial aircraft during approach. This manuscript reports the results from the ALLEGRA (Advanced Low Noise Landing (Main and Nose) Gear for Regional Aircraft) project. This project assessed the performance of several highly realistic low–noise technologies (LNTs) applied to a detailed full–scale nose landing gear (NLG) model in aeroacoustic wind–tunnel experiments. Four individual low–noise concepts tested, namely a ramp door spoiler, a solid wheel axle fairing, wheel hub caps, and multiple perforated fairings. Combinations and small variations of some of these LNTs were also evaluated. The use of multiple planar microphone arrays allowed for the application of 2D and 3D acoustic imaging algorithms to assess the location and strength of the noise sources within the NLG system in different emission directions for each configuration. The wheel axle, the inner wheel hubs, the steering pinions and the torque link were identified as the noisiest NLG elements. The solid wheel axle fairing was the most effective individual LNT, and it improved its performance when applied in combination with the ramp door spoiler and wheel hub caps, reaching overall noise reductions of more than 4 dBA.

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.

One of the major tasks in the design and optimization process of a new landing gear system for an unmanned aerial vehicle (UAV) is to accurately determine the loads during the landing event, especially if the landing gear is considered unconventional. The work being presented describes a new approach to simulate landing events for some of the UAV's unconventional landing gears produced by General Atomics Aeronautical Systems, Inc. (GA-ASI), such as Predator A and Predator B series. GA-ASI selected ABAQUS/Explicit®, which is part of the ABAQUS suite of finite element analysis software, for its nonlinear, transient dynamics capabilities. The tricycle landing gear systems in Predator A and Predator B consist of a very stiff nose strut equipped with a shock absorber and highly flexible main gear struts made out of composite materials designed to absorb the landing event with elastic strain energy and frictional energy dissipation with tire scrubbing. The peak loads during the landing event are highly dependent on the complicated ground interactions with the tires during the initial contact and spin-up event. Geometric nonlinearity effects due to large displacements in the composite struts are accounted for in ABAQUS/Explicit®. The tires are modeled in detail with internal pressure simulated by hydrostatic fluid elements and the rubber material represented by hyperelastic elements embedded with rebar elements to model the tire reinforcements. A slip-rate based friction model governs the contact behavior between the tires and the ground. Landing gear struts are modeled using beam elements with stiffness validated by empirical load-deflection data. Shock absorbers' elastic and damping characteristics are defined by connector element behaviors. Bearing friction at the nose landing gear shock absorbers' piston-cylinder interface is also considered. Simulation results show a time history of landing loads at the wheel axles and deflection for the landing gear struts during the entire landing event. The results are then compared to and validated by extensive test data.

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.

Aircraft interacts with the ground through landing gear system, while taxiing down the runway.Under rain or snow conditions, water film splashed by aircraft tires during taxiing on water-covered runways adheres to the landing gear, leading to ice accretion under low-temperature conditions, which may directly compromise aircraft takeoff and landing safety. Due to the substantial resource consumption required for experimental investigation of this problem, numerical simulation was employed to model the phenomenon.The water film icing process can be divided into two main stages: the formation of water film on the landing gear caused by tire spray, and the subsequent icing and heat transfer process of the splashed water film on the landing gear, this study conservatively simplifies the tire spray phenomenon as a typical liquid-solid two-phase coupling problem. A Finite Volume Model simulating water accumulation dynamics on landing gear tires was developed in Fluent software, based on extreme runway water accumulation conditions and extreme navigation weather scenarios during takeoff of a domestic civil aircraft model. The model incorporates coupled tire-water film-landing gear interactions. The VOF (Volume of Fluid) model and mesh motion are employed to calculate the water film thickness on the landing gear. A conservative thermodynamic equilibrium equation is then constructed based on boundary conditions to estimate the ice accretion thickness. The article analyzed the influence of external factors (aerodynamic drag, gravitational force, etc.) on water film thickness. The calculation results indicate that a conservative estimation of ice accretion derived from water film thickness does not compromise takeoff and landing safety, thereby validating that under rainy or snowy weather conditions with water accumulation on the runway, the conservative maximum icing thickness resulting from wheel spray water and landing gear water accumulation during aircraft taxiing will not exceed a level sufficient to pose a threat to aircraft takeoff and landing safety.

A unique, beneficial feature of rotorcraft is their flexibility in aircraft-to-ground interfacing. For a variety of reasons, hard landings can occur when the descent rate of the aircraft is larger than intended. The resulting impact can result in vehicle damage, structural failure, injuries, etc. To reduce these risks, an attractive solution is the implementation of a robotic legged landing gear (RLLG) system. The system softens a hard landing by acting as a shock absorber with a relatively large stroke, allowing the aircraft to decelerate over a much larger distance compared with a tradition landing gear system. This paper explores the mitigation of rotorcraft hard landings via RLLG through a comprehensive multibody dynamics simulation tool. The purpose of this study is to demonstrate the efficacy of the RLLG as a robust solution to reduce loads during hard landings for multiple landing configurations. The results show that when using RLLG in place of conventional landing gear, peak loads are reduced by approximately 70–90%, depending on the landing conditions. Through Monte Carlo simulation, robotic landing gear system performance is shown to be robust to uncertain conditions.

Landing gear systems are an essential component of any aircraft, requiring precision and reliability to ensure safe operation. This research advances previous work on landing gear automation that utilized hydraulic systems with an electrical interface. It introduces an improved landing gear design by integrating Programmable Logic Controller (PLC) technology. Automation ensures smooth, efficient, and reliable retraction and deployment, enhancing overall performance, safety, and reliability. At the heart of the research is a PLC-based framework that controls landing gear actuation with exceptional precision. The modular, scalable design allows adaptation to different aircraft sizes and configurations, making it versatile for various applications. This flexibility supports both educational demonstrations and potential integration into more advanced aerospace projects. The research incorporates a Proportional-Integral-Derivative (PID) controller alongside PLC technology to enhance system performance. The PID controller refines actuator movement by dynamically adjusting hydraulic pressure and control signals based on real-time feedback. This integration ensures smoother transitions, minimizes mechanical stress, and enhances stability under varying conditions. By leveraging PLC and PID control, the system achieves optimal responsiveness and precision, improving safety and efficiency. The primary objective of this research is to serve as an educational tool, bridging the gap between theoretical concepts and practical engineering applications. It provides researchers with hands-on experience in advanced automation technology. Experimentation with this system deepens understanding of automated control systems and their role in modern aerospace engineering. The demonstration model offers an accessible platform to explore automation principles and their impact on traditional mechanical systems in aviation. This research also emphasizes simplicity, efficiency, and reliability. By focusing on core landing gear functions, it demonstrates how automation can streamline processes. PLC technology improves operational efficiency, reduces manual input, and ensures consistent performance. The PID controller further enhances adaptability by fine-tuning system responses for precise actuation under different loads and environmental conditions. While primarily educational, this research sets the stage for advancements in intelligent landing gear systems. Its modular design ensures compatibility with future technological innovations, making it a valuable foundation for ongoing aerospace automation research. Integrating PLC with PID control also creates opportunities for advanced fault detection, predictive maintenance, and adaptive control algorithms in future implementations. In conclusion, this research represents a forward-thinking approach to aerospace engineering, emphasizing automation’s role in improving safety, reliability, and efficiency. By combining cutting-edge technology with practical application, it addresses current challenges and inspires future aviation innovations. This study contributes to the development of smarter, safer, and more efficient aircraft systems, offering significant value for education, research, and technological advancement.

Aircraft landing gears are currently optimised to have optimal performance in the rare case of a hard landing. The resulting suspension layout may lead to unsatisfactory oscillations when the aircraft is taxiing on a rough runway; runway unevenness can excite elastic structural modes, leading to passenger and crew discomfort. Although there are existing modifications of aircraft shock absorbers to reduce the problem, the basic design conflict between the requirements for landing and for rolling cannot be fully overcome by a passive suspension layout. Semi-active suspension techniques promise a solution to this problem. A semi-active suspension, i.e. a damper with a variable, controlled orifice cross-section, is capable of reducing fuselage vibrations effectively while being relatively light-weight and low system complexity. In this thesis, three control laws, a skyhook-type controller, a fuzzy-logic controller, and a state feedback controller are designed for the application to a semi-active suspension for an aircraft nose landing gear. Regarding the aircraft flexibility, the landing gear can no longer be designed independently from the aircraft. The layout of the controllers is therefore undertaken using an integrated design approach. Airframe and landing gear properties are determined taking into consideration models from different engineering disciplines involved in the aircraft development process, making the oleo design part of the concurrent engineering loop. The aircraft model is set up in a multibody simulation environment. The control laws are developed in a control design tool; special consideration is given to the requirements of semi-active actuators. The controllers are exported into the simulation environment and their parameters are optimised by means of multi-objective optimisation. In a further step, the performance of the three control strategies are compared with each other and additionally with passive and fully active approaches. The dependence of the control performance on operational parameters (aircraft weight and speed, runway roughness) is assessed, and limitations due to realistic actuators restrictions are discussed. Finally, the benefits and disadvantages of semi-active nose landing gear control are summarized and open problems are addressed.

: This report covers the work performed on the advanced helicopter landing gear program by Hughes Helicopters. The objectives of the program were to design, fabricate, and test a wheel-type advanced main landing gear concept possessing high-energy-absorbing characteristics for helicopters in the 15,000-pound class. These objectives were achieved by formulating design criteria through a data search, choosing the most cost-effective composite material, and through a design analysis, selecting the most promising landing gear concept. This concept used graphite epoxy as a structural material to fabricate the trailing arm of the main landing gear of the Hughes YAH-64 helicopter by wet-filament winding (WFW). The graphite arm was successfully tested, demonstrating the practicality of employing composite structures in the construction of high-energy-attenuating landing gear components. The program showed that the graphite trailing arm was 11 percent lighter than the baseline steel arm. The weight of the baseline landing gear could be reduced by maximizing the use of composites: 7 percent by using existing WFW equipment, and 26 percent by developing and using a toroid winding machine. (Author)

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.

This paper describes a numerical procedure for the prediction of aircraft noise certi cation metrics starting from the aircraft trajectory. The procedure is applied to the nose landing gear of a Gulfstream business jet. The numerical core of the procedure is a hybrid aeroacoustic method based on a lattice Boltzmann ow simulation and a Ffowcs-Williams & Hawkings noise propagation computation. The hybrid method is initially validated by computing the noise generated by a geometrically simpli ed model of the same landing gear installed on a at plate and comparing wall pressure and fareld noise spectra with wind-tunnel measurements. The same numerical method and a similar discretized model are then employed to compute the unsteady ow eld past the real landing gear deployed under the aircraft. The upstream ow conditions are the same occurring during a ight along a \nominally constant descent trajectory at the nearest point to the ground microphone. Comparisons between the predicted noise levels and the measured ones during a ight test, with only the nose landing gear deployed and other airframe and engine sources kept at their admissible minimum, are in good agreement.