Aircraft Braking Research Articles

Experimental and Analytical Investigation of Aircraft Brake Pad Material Composition

In the field of aviation industry, the aircraft braking system serves for ground taxing operation, ability to hold the aircraft at full static run-up and to stop the aircraft during landing. As usage of braking system increases, the frictional parts of the braking system undergo wear when it contacts with the rotor disc. To optimize the reliability of brake pads, finding suitable material is essential. This work is carried out to make a better frictional material with superior mechanical properties to sustain the environment. Identification of suitable composition was found satisfactory with help of adding and removing the set of constituent materials. Six sample brake pads with different materials and numerous compositions were manufactured through the powder metallurgy process. The necessary machining operations were performed to get a required shape. Theoretical calculations and analysis were done to establish the enhanced mechanical properties including wear and hardness. It was observed that samples 1 and 3 have better wear resistance and wear rate for different loading conditions.

Wear Behavior of Commercial Copper-Based Aircraft Brake Pads Fabricated under Different SPS Conditions

Understanding the wear behavior of Cu-based brake pads, which are used in high-speed railway trains and aircraft, is essential for improving their design and safety. Therefore, the wear mechanism of these pads has been studied extensively. However, most studies have focused on the changes in their composition and not the effects of their manufacturing conditions. In this study, we fabricated commercial Cu-based brake pads containing Fe, graphite, Al2O3, and SiO2 using spark plasma sintering under different conditions. The microstructures and mechanical properties of the pads were investigated. The pads were tribo-evaluated using the ball-on-disc test under various load conditions. Their worn surfaces were analyzed using X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and confocal microscopy in order to elucidate their wear mechanism. In addition, the dynamometer test was performed to confirm whether their wear behavior would be similar under actual conditions. Finally, a comparative analysis was performed using the ball-on-disc test. The results indicated that the brake pads with the same composition but fabricated under different sintering conditions exhibited different wear characteristics. We believe that this research is of great significance for understanding the wear mechanism of Cu-based brake pads and improving their design and hence their performance.

ASSESSING THE IMPACT OF THE SLOPES ON RUNWAY DRAINAGE CAPACITY BASED ON WHEEL/PATH SURFACE ADHESION CONDITIONS

Aircraft braking distance is dependent on the friction between the main gear tires and runway pavement surface.Pavement texture, which is divided into macrotexture and micro-texture, has a noticeable effect upon friction, especially when the surface is wet. A risk analysis framework is developed to study the effects of longitudinal and transverse slopes on the aircraft braking distance in wet runway conditions and their influences on the probability of landing overrun accidents.This framework is operating under various water-film thicknesses, Maximum Landing Weights (MLW), and touchdown speed probability distributions for an acceptable range of longitudinal/transverse slopes and pavement texture depths.A simulator code is developed that initially computes the existing water-film thickness, as the result of intense precipitation,under aircraft main gear (depend on aircraft category) and then applies this variable as one of the main inputs to the aircraft braking distance computation. According to the obtained results, longitudinal gradient does not have a significant effect on the existing water depth on the surface although it affects the flow path length. Furthermore, 1% to 1.5% transverse slope causes rapid drainage of water from the runway surface and considerably decreases the probability of runway excursion accidents.

Fatigue life analysis of an aircraft brake component to prevent damage and ensure operational safety

Safety is critical at all stages of aircraft operations, from air missions to ground operations. One of the most important airframe systems that affects ground safety efficiency is the wheel brake system. The brake is used to brake the aircraft from the moment the wheels touch the ground. During braking, the brake components are exposed to high temperatures and high dynamic stresses, which affect their wear and service life. The brakes of heavy aircraft are especially prone to overheating during landing and taxiing on the ground. The paper deals with fatigue analysis of two brake discs used in civil transport aircraft for short and medium haul. The aim of the study is to assess which variant reduces the risk of brake overheating problems and thus contributes to increased operational safety. In the paper, the principle of operation of a multiple-disc aircraft brake is thoroughly explained, including the loading conditions and the causes of disc failures. Geometric CAD models of discs were obtained by reverse engineering methods and the lifetime analysis was performed numerically using the finite element method.

Numerical simulation of temperature field in a C/C composite multidisk brake during aircraft braking

This article presents a finite element method for simulating the heat production during stopping the aircraft. Thermal analysis and simulation in the finite element model are based on the theory of energy transformation and transportation. A commercial software COMSOL Multiphysics 5.5a is used for simulating the braking operation. The internal temperatures of the brake disks were obtained and the variation in temperatures between disks were discussed. Thermomechanical behaviour is studied to show the effect of thermal energy on the contact mechanics for the friction surfaces between the brake disks. Aircraft mass, initial velocity and deceleration rate are responsible for heat generation and consequently the maximum reached temperature during braking. The friction surfaces between disks were the main heat energy source where the heat was concentrating on these layers of friction surfaces. For the selected braking operation, the maximum reached temperature was 1020K. The finite element model was validated against historical data for a Boeing737-400 at constant deceleration for new disk brakes and for RTO brake energy.

Design and Verification of Two-Stage Brake Pressure Servo Valve for Aircraft Brake System

Wheel braking devices is some of the most widely used landing deceleration devices in modern aircraft. Jet pipe pressure servo valves are widely used in large aircraft wheel brake control systems because of their high anti-pollution ability, high sensitivity and fast dynamic response. However, most brake systems suffer vibration phenomena during the braking process. The pressure servo valve is an important part of the hydraulic brake system, and also an important factor affecting the vibration of the system. In order to solve the vibration problem in the brake system this paper present a two-stage brake pressure servo valve design. We place feedback channels at both ends of the main spool to stabilize the output pressure. In addition, modeling, simulation and experimental verifications are carried out. Firstly, the principle and structure of the pressure servo valve are described. An accurate mathematical model of the two-stage brake pressure servo valve and the testing system is established. Then a simulation analysis is carried out. Finally, a two-stage brake pressure servo valve testing experimental platform system is built for experimental verification. The experimental results show that the mathematical model of the two-stage brake pressure servo valve and the test system established in this paper have high accuracy, and the designed servo valve structure can restrain vibrations. The above research results provide a useful theoretical reference for performance optimization, stability analysis and valve body structure improvement of brake pressure servo valves.

Effect of cooling rate on C92900 bronze microstructure and properties

In the mechanical engineering, antifriction tin bronzes are used for the manufacture of friction parts. For example, the C92900 bronze has found use in aircraft braking system components. One of the ways to improve the properties of leaded tin bronzes is to increase the cooling rate during solidification. This paper studies the effect of the cooling rate and changes in the content of alloying elements within the limits established by the C92900 bronze industry standard OST 1 90054-72. In order to provide different cooling rates, the prepared alloys were casted into molds made of resin-bonded sand, steel and graphite with cooling rates 0.4, 5.0, and 14.6 °C/s, respectively. The influence of the cooling rate and the bronze composition on the freezing range, macrostructure, microstructure, thermal conductivity, mechanical, and tribological properties were investigated. Differential thermal analysis demonstrated that the upper-limit alloying of C92900 bronze leads to a decrease of the solidus temperature by 40 °C, which should be considered during deformation processing and heat treatment. An increase in the cooling rate during C92900 bronze ingot solidification provides a significant grain refinement and changes the amount, size and morphology of phases. For example, in case of metallic and graphite mold casting, the size of lead particles decreases, and its circularity increases. The change in the Sn content within the range established by the industrial standard has a significant effect on the γ-(Cu,Ni)3Sn intermetallic phase fraction. The increase in the cooling rate has no significant effect on the C92900 bronze thermal conductivity but increases hardness by 30 HB as well as cooling rate and yield strength and ultimate tensile strength. Wear tests carried out in accordance with the «shaft – partial insert» scheme in a kerosene medium using a steel counterbody showed that an increase in the cooling rate during solidification leads to an increase in the bronze wear rate from ~0.4·10–8 to ~1.2·10–8. The change in the bronze composition within the industrial standard range has practically no effect on the wear rate but leads to a slight increase of the coefficient of friction.

Chattering Suppression Fast Terminal Sliding Mode Control for Aircraft EMA Braking System

The performance of the electromechanical actuator (EMA) in the aircraft braking system suffers from the system’s nonlinear characteristics, whereas the robust control can contribute to the improvement of tracking precision in its servo system. In this article, a chattering suppression fast terminal sliding mode (FTSM) control strategy with an embedded nonlinear disturbance observer (NDO) is proposed for the EMA braking system, which can retain the fast convergence characteristic of the classical FTSM and guarantee the system converges to equilibrium point timely. Moreover, the singularity problem of the classical FTSM control is resolved through the well-designed sliding mode manifold. The NDO is designed to estimate the uncertain factors online, including time-varying parameters, external disturbance, and unmolded dynamics of the EMA system. By applying the compensation terms into the control law, the proposed control strategy can alleviate the chattering problem and improve system stability. To verify the performance of the proposed control strategy for EMA, wheel braking tests are conducted under various conditions regarding the type of runway and failure cases. The results indicate that the proposed control strategy can guarantee the servo performance, the control precision, and the response speed of the EMA servo system.

A novel aircraft anti-skid brake control method based on runway maximum friction tracking algorithm

As a dominant type of disturbance during aircraft braking, variation in maximum friction between the runway and the tires largely affects the efficiency of aircraft anti-skid braking systems (ABS). Conventional aircraft anti-skid braking control method, such as pressure-bias-modulated (PBM), are unable to identify and track the changing maximum friction between the runway and the tires, which results in reduced braking efficiency and long braking distances. This paper presents a novel anti-skid braking control method which can identify and track the maximum friction using only wheel angular velocity and brake pressure signals. An extended braking stiffness (XBS)-based runway maximum friction identification method is proposed to determine the runway maximum friction, where XBS is the differential of the friction to the differential of the slip ratio. Tracking differentiator (TD) is employed to derive the corresponding differential signals, which enables XBS to be calculated efficiently, without compromising calculation accuracy. By analyzing the dynamic characteristic of the wheel, a runway friction characteristic observation function is designed to observe changing friction characteristic during the entire braking. To be able to track the varying maximum friction in real time, a runway maximum friction tracking algorithm is designed, which can realize accurate brake pressure control according to the change in runway friction characteristic. The Lyapunov function is employed to prove the stability of the designed controller. Simulation tests are carried out under multiple sets of changes in runway friction characteristic. The comparison simulation test with PBM algorithm shows that the designed control method greatly improves the braking efficiency. Ground inertia test bench experiments are also conducted to further verify the correctness and effectiveness of the proposed aircraft anti-skid brake control method. Simulation and experiment results prove that the proposed control method is able to identify and track the varying maximum friction provided by different runways. The results of experiment also demonstrate that the control method still has good robustness and performance, even with the objective noise of the system.

Techniques and Methods for Runway Friction Measurement: A Review of State of the Art

Accidents in which aircrafts veered off the runway when landing have occurred frequently, which pose a considerable threat to people's lives and property. Friction, produced by the contact patch between the tires and the runway, has long been known as a crucial factor for a safe landing. Therefore, accurately measuring the friction coefficient (F-Coe) is regarded as an effective means to reduce accidents, especially in extreme weather. This review article aims to summarize and analyze the state-of-the-art techniques of runway friction characteristics measurement to provide all stakeholders a broader understanding and more valuable references. First, the methods available for measuring (or estimating) the friction characteristics are reviewed, such as American Society of Testing Materials (ASTM) standard test, the caused-based method, the effect-based method, modeling method, and fusion method. Second, the pros and cons of these methods are discussed from two aspects: conventional method and the tribo-system-based method. Third, the research progress of the correlation between the F-Coe obtained by ground measurement equipment and the aircraft braking F-Coe (ABF-Coe) is summarized and discussed. Finally, the measurement policies, about runway surface friction characteristics, proposed by International Civil Aviation Organization (ICAO), Federal Aviation Administration (FAA), and European Aviation Safety Agency (EASA) in recent years are summarized and the measurement methods are proposed or improved according to these policies. For developing better and proper measurement methods of runway F-Coe (RF-Coe), the future envisaged research lines should focus on the new measurement techniques and methods under the joint action of tires, runway, contaminants, and atmospheric condition.

Evaluating the parametric, semi-parametric and nonparametric models for reliability in aircraft braking system

It is assumed that the lifetime of a system is a random variable valued based on a probability model and reliability studies with a system as a function of time. In this study, by multi-layers and hierarchical coding, we initially recognize the common operations and then, considering the sources likely to cause a crash, the crash center will be detected followed by estimating the structure of reliability of model. In this study, the aircraft wheel braking system has been broken down to its existing sub-systems and finally a reliability engineering model has been provided for wheels braking system and it has been estimated using existing methods whether nonparametric, semi-parametric and parametric approaches based on attrition and accelerated attrition. Then, among provided models, the most suitable model with least risk of square root of error has been fitted for studied data.

Evaluating the interaction between engineered materials and aircraft tyres as arresting systems in landing overrun events

According to the registered databases of air accidents around the world, landing overruns are the most probable accidents among all runway excursion events. Although new aircraft are enhanced with the latest technologies that improve the maneuvers safety, the frequency of landing overruns are bound to increase because of the ascending growth rate of annual traffic. The principal scope of this paper is to evaluate the functionality of Engineered Materials Arresting System (EMAS) as a mitigation strategy to reduce the possible consequences of landing overrun events and in particular to determine if installing an EMAS can help land-locked airports to meet Federal Aviation Administration (FAA) recommendations in order to upgrade their Runway End Safety Areas (RESAs). In the previous studies, not enough investigations are dedicated to predicting the behavior of the aircraft and its deceleration rate after interfering EMAS and how different materials as arrestor beds would modify aircraft braking distance in RESA. Therefore, secondary objective of this paper is to determine the most optimum height of EMAS slabs, in function of execution costs and accident severity reduction rate. In this regard, a MATLAB®-based numerical code, which simulate the tire-pavement interface, is developed in order to evaluate the functionality of EMAS for aircraft ground maneuvers. Although this code is developed for both dry and wet runway conditions, dry runway’s surface is selected as the boundary condition of this study. It simulates aircraft arresting distance by calculating a dynamic skid resistance between aircraft main gear and runway pavement with a fix time step. The results are plotted as risk contour intervals on the layout of EMAS that is installed at the RESA. In addition, this numerical code is adopted in order to perform a sensitivity analysis on five arresting bed materials, which consist of three low-density concretes with maximum crushing stress thresholds of 172500, 345000 and 930000 Pa, one gravel-based material and one foam aggregate-based mixture. Among all, low-density concrete with the highest crushing strength causes shorter aircraft arresting distance.

Development of Efficient Algorithms for Predicting Aircraft's Braking Mode

In this paper, a methodology to design algorithms for predicting the aircraft’s braking distance is presented. An efficient predicting algorithm based on the energy approach to aircraft control is developed. A new forecast correction concept is proposed. With this concept, the predicting accuracy is improved, and the degree of confidence in the predicting results is increased. Statistical tests of the algorithms under different runaway conditions and different aircraft configurations are performed. The predicting reliability is proved.

Study on modal characteristics and vibration reduction of an aircraft rotor–stator brake-induced squeal system

Based on the modal coupling theory, the rotor and stator contact stiffness and axial relative velocity are considered to build an electric aircraft brake dynamic system model in this study. Both the complex modal analysis and transient dynamic analysis methods are used to study the aircraft brake squeal performance and vibratory mechanism. The unstable vibration modes indicate that the out-of-plane vibration plays an important role and the feed-in energy is larger than the output energy in the brake rotor–stator module so that brake squeal takes place. Then the influences of the contact stiffness, friction damping and frictional coefficient on the brake squeal system are carried out, laying the foundation for the three proposed vibration suppression methods. Results show that the coefficient negative-slope condition will intensify the vibration. Also, a linear relationship between the squeal factor and the frictional coefficient is obtained to provide a guidance to predict squeal stability under more conditions. Vibration reduction design shows that adding a damping layer to the brake mechanism and chamfering the edge of braking stators both can reduce brake squeal effectively, while slotting braking stators is invalid in aircraft braking system.

A power-by-wire aircraft brake system based on high-speed on-off valves

The aircraft brake system plays a recognized crucial role as a fundamental subsystem. Conventional aircraft brake actuators are powered by centralized hydraulic source, engine driven pump (EDP). The proper operation of aircraft braking requires many accessories, such as long, complex pipelines and pilot-operated servo valves, which are located near the landing gear and exposed to cold high-speed airflow and possible obstacles, where the environment is harsh to cause many problems such as vibration even leakage. To improve the safety and maintenance of aircraft, a novel concept of power-by-wire aircraft brake system (PWABS) is proposed in this paper. It only consumes electric power from the aircraft to implement the brake function instead of hydraulic fluid. Thus, the long, complex hydraulic pipelines are replaced by electric power cables, cutting the weight of aircraft utility systems; besides, the leaks of the pilot stage of servo valves are also reduced by replacing servo valves with on/off valves to save the power input from aircraft. Above all, that aircraft brake system can work as usual even when the airborne hydraulic source is lost, which benefits the aircraft safety considerably. This paper presents the working principle and the configuration of PWABS, and parameters of which are designed. Dynamics models of PWABS and aircraft taxiing are established. Based on specific models, a nonlinear adaptive backstepping (NAB) control strategy is introduced for the system control, simulations are carried out to verify the practicality, a prototype is developed, and experiments are conducted on an inertia brake test bench to investigate the performance. The present results demonstrate the feasibility of PWABS and provide a better choice for more-electric aircraft braking systems.

Estimation for Runway Friction Coefficient Based on Multi-Sensor Information Fusion and Model Correlation.

Friction is a crucial factor affecting air accident occurrence on landing or taking off. Tire–runway friction directly contributes to aircraft stability on land. Therefore, an accurate friction estimation is a rising issue for all stakeholders. This paper summarizes the existing measurement methods, and a multi-sensor information fusion scheme is proposed to estimate the friction coefficient between the tire and the runway. Acoustic sensors, optical sensors, tread sensors, and other physical sensors form a sensor system that is used to measure friction-related parameters and fuse them through a neural network. So far, many attempts have been made to link the ground friction coefficient with the aircraft braking friction coefficient. The models that have been developed include the International Runway Friction Index (IRFI), Canada Runway Friction Index (CRFI), and other fitting models. Additionally, this paper attempts to correlate the output of the neural network (estimated friction coefficient) with the correlation model to predict the friction coefficient between the tire and the runway when the aircraft brakes. The sensor system proposed in this paper can be regarded as a mobile weather–runway–tire system, which can estimate the friction coefficient by integrating the runway surface conditions and the tire conditions, and fully consider their common effects. The role of the correlation model is to convert the ground friction coefficient to the grade of the aircraft braking friction coefficient and the information is finally reported to the pilots so that they can make better decisions.

Design for System Safety Analysis of the Aircraft Braking System Having Normal and Emergency Wheel Braking

Design for System Safety Analysis of the Aircraft Braking System Having Normal and Emergency Wheel Braking - written by Rolwyn Marian Cardoza , Dr. M. Krishna published on 2020/07/06 download full article with reference data and citations

Tire-Wear Control in Aircraft via Active Braking

In ground vehicles, tire consumption is, in general, mainly due to the mileage covered, and in fact, the life span of tires, at least in common situations, is rather long. In the aeronautical context, and for aircraft in particular, instead, tire consumption plays a crucial role in determining the maintenance costs. This is due to the fact that, in aircraft braking, nearly all maneuvers activate the antiskid controller, which remains in use for long time intervals. In ground vehicles, instead, anti-lock braking systems (ABS) are usually active for short time intervals that cover a part of the braking maneuvers only. Thus, tire consumption in the automotive context is usually studied under constant speed assumptions. In this article, we formulate a tire consumption model that encompasses explicitly the wheel acceleration/deceleration dynamics and show that tire wear can be directly related to the antiskid controller parameters. Based on this, a sensitivity analysis of tire consumption versus braking performance is carried out, showing that, using an appropriate antiskid control approach, one may directly formulate the braking problem as a tire consumption regulation one, being sure that the resulting braking performance will have an a priori guaranteed outcome. The tire-wear model is also validated in an experimental setting.

Aircraft Ground Braking Assistant Control Based on Pilot Control Model

Aircraft ground braking control is a complex time-varying dynamic problem, especially when there are unexpected disturbances from lateral wind or visual error. Therefore, under some extreme conditions, it is hard for the pilot to control aircraft braking as well as usual without assistant control. This paper solves this problem by proposing a novel assistant control for aircraft ground braking, mainly based on the pilot control model and the LPV theory. And in order to reflect the control characteristics of the pilot, the sensory and control-theoretic model were combined together for controller designing. To test the performance of proposed control method, a real time pilot-in-loop simulation system is constructed. According to experiment results, the proposed assistant control shows better performance than pilot control, for it not only help the pilot to resist disturbance, but also hardly run counter to the pilot’s intent.

Effect of Type of Carbon Matrix on Tribological Properties of C C Aircraft Brake Discs

Four type of Carbon/Carbon (C/C) composite brake discs (A, B, C, D) were manufactured using different process routes, using spun yarn graphitised carbon fabric as reinforcement. These discs were densified with different types of carbon matrices derived from different precursor materials. C/C brake disc of type A is having carbon matrix derived from pitch precursor, type B has a mixture of resin and pitch derived carbon matrices, type C has a combination of resin derived, pyro and pitch derived carbons and type D has pyro and pitch derived carbon matrices. Friction and wear performance of these brake discs were studied by simulating aircraft landing braking energies (normal and over load) corresponding to one interface using disc-on-disc dynamometer. It was found that the type of carbon matrix influences the nature of friction film formed, which in turn affects the wear rate of C/C brake discs. It was also discussed how the matrix characteristics affected the mechanical properties and the friction film formed affect the coefficient of friction of each type of disc.