Aircraft Braking Research Articles

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.

Influence of B4C on oxidation resistance of PSN/borosilicate glass-B4C field-based repair coating of C/C aircraft brake materials at 700–900 °C

PSN/borosilicate glass-B4C coating was designed for use as field-based repair coating on carbon/carbon (C/C) composites for aircraft brakes. The first PSN layer was transition layer that improved wettability between glass coating and C/C, and the second layer of borosilicate glass-B4C formed outer glass layer. Effect of B4C content on oxidation behavior of C/C repair coating was investigated. The coating with 25 wt% B4C demonstrated excellent oxidation resistance and could effectively protect C/C composites from oxidation. Weight losses of −3.1% at 700 °C and −2.9% at 900 °C were observed after being oxidized for 10 h. Repair coating with smooth, dense, and crack-free structure could be rapidly formed as B4C content of the coating increased to 25 wt% and 35 wt% with increasing oxidation time. B4C in repair coating could be oxidized into B2O3 glass and it could heal defects in the coating. Residual B4C dispersed in the coating could dispersion strengthen glass coating and inhibit crack formation in the coating.

Tribological Behaviour of Graphite-Reinforced FeNiCrCuMo High-Entropy Alloy Self-Lubricating Composites for Aircraft Braking Energy Applications

In the present study, the graphite-reinforced FeNiCrCuMo high-entropy alloy-based self-lubricating composites are fabricated through the powder metallurgy. The sintering temperatures (900 and 1000 °C) are varied to study the densification and properties of the composites. The composites are characterized for microstructure, density, and hardness. The brake performance of the composites is evaluated for the braking condition of a military aircraft. The microstructure consists of two phases: one phase (lamella structure) rich with the Fe, Cr, C, and Cu and another white phase rich with the Ni, Cu, C, and Fe along with the uniformly distributed graphite. The EDS analysis confirms the presence of Fe, Cr, Ni, Cu, and Mo in the matrix. The composite sintered at 1000 °C shows improved densification, high hardness, high wear resistance, and excellent braking performance. With the increase of braking energy (speed), the wear rate increases due to the increased intensity of abrasive wear, oxidation wear, and plastic deformation-assisted wear, whereas the friction coefficient has not changed much. Low porosity content and mild abrasive wear are responsible for the high wear resistance in the composite sintered at 1000 °C. Compared to the C/C, C/SiC C/C/SiC composites and Fe- or Cu-based composites, the high-entropy alloy-based composites show great potential for improved braking properties in the high-energy braking applications.

A Brush-based approach for modelling runway friction assessment device

ABSTRACT This paper deals with the modelling of friction forces measured by runway friction assessment device. The Brush model has been modified to introduce the effect of water at the scale of the tire and the scale of the tire/runway contact area. Extensive experimental campaigns have been carried out to calibrate and validate the model with the IMAG (Instrument de Mesure Automatique de Glissance). Results show that the developed model can reproduce satisfactorily the measured friction-slip curves for different vehicle speeds, water depths and surface textures. The model also provides a better understanding of experimental results concerning friction on wet runways. In particular, it highlights the role of the tire/runway contact length, which governs the decrease of the friction coefficient and the initial slope of the friction-slip curve when the speed increases. Discussions are made in terms of benefits of the model for applications such as the prediction of aircraft braking friction or the harmonisation of friction measuring devices.

Fracture toughness evolution of a carbon/carbon composite after low-cycle fatigue

High fracture resistance of carbon/carbon (C/C) composites as a material for aircraft braking systems is essential for their safe service. This paper presents a study on fatigue behavior and residual mechanical properties after cyclic load of discretely-reinforced C/C composite. The influence of cyclic loads on the fracture toughness of frictional C/C composite was examined. Results of fracture toughness tests after compression fatigue load were determined using the ASTM single-notch three point bend test and correlated with fracture surface using scanning electron microscopy (SEM). It is revealed that C/C composite fracture toughness strongly depends on the fiber–matrix interfacial bonding strength. Cyclic loads below fatigue limit improve residual fracture toughness of the material up to 25% by the mechanism of interfaces weakening. Cyclic loads above fatigue limit decrease residual fracture toughness of the material by the fracture of carbon fibers. Observed results may be useful in developing friction C/C composites to enhance fracture resistance in aircraft braking systems, increasing safety and operating lifetime.

Frictional Heating in Railway Brakes: A Review of Numerical Models

In the design process of a railway vehicle it is crucial to determine the operating temperature of the brake friction elements. The thermal load related to braking depends on both the design of the vehicle and its braking system but also on the operating conditions in service. It is therefore justified to model frictional heating of the friction elements in the design phase. As railway braking differs substantially from automotive or aircraft braking, current review article is focused on the published literature concerning specifically modelling of railway tread and disc brakes. However, to present the complete picture of the state-of-the-art, studies undertaking related topics concerning frictional heating are also discussed. It is concluded that the existing models should be further developed to account for mutual coupling of operation conditions and the coefficient of friction.

Identification of the heat flux generated by friction in an aircraft braking system

In this paper, we present an estimation of the heat flux generated by friction under real aircraft braking conditions using an inverse method. The estimation is performed considering an assumption of 1D transient model and multiple interfaces. This model takes into account a non-perfect description of the thermal contact. Then, an identification of the generated heat flux by friction in the different interfaces from experimental data is performed using a linear temporal evolution parameterization of this parameter. The reconstruction of the thermal field from identified generated heat fluxes provides some very low residues. The comparison between the thermal energy identified by the inverse method and mechanical energy absorbed on the test bench validates the results.

Relationship between microstructure and tribological behavior of CFRC composites

Carbon fiber reinforced carbon (CFRC) composites were initially introduced in spacecraft propulsion area and quickly started to be applied in aircraft braking systems, replacing conventional metallic systems, thanks to their excellent tribological properties. Each company develops their own CFRC composite production system, the information is unique to each manufacturer, and little is reported in the literature. In this work, tribological characterizations of three commercial CFRC composites are performed using a pin-on-disc tribometer. The results showed that the pairs assembled with pyrolytic matrix composites of rough or smooth laminar texture with graphitization index between 18 and 40% has an average COF between 0.15 and 0.25, while the pairs assembled with mixed pairs, pyrolytic matrix and glassy matrix, or pair of glassy matrix display average COF between 0.10 and 0.15. Wear which can reach a rate 9 times higher to the tribological pair of glassy composite when compared to a pyrolytic composite.

Research on HILS Technology Applied on Aircraft Electric Braking System

On the basis of analyzing the real-time feature of hardware-in-the-loop simulation of aircraft braking system, a new simulation method based on MATLAB/RTW (Real-Time Workshop) and DSP is introduced. The purpose of this research is to develop a digital control unit with antilock brake system control algorithm for aircraft braking system using HILS. DSP is used as simulator. Using this method, a detailed mathematical modeling of system is proposed first. Studies on reducing sampling time with model simplification and modeling for applying to I/O interface of DSP and HILS are conducted. Compared with other methods, this method is low cost and convenient to implement. By using these methods, we can complete HIL simulation of aircraft braking under various experimental conditions, modify its control laws, and test its braking performance. The results have demonstrated that this platform has high reliability. The algorithm is verified by real-time closed loop test with HILS system and the results are presented.

Reduction Methods Applied to Aircraft Brake Squeal Prediction and Simulation

Aircraft braking systems may be subjected to friction-induced vibrations, during which the brake is unstable and behaves as a source of mechanical vibrations. This is an issue for aircraft brake manufacturers because it may jeopardize structural integrity due to accelerated fatigue life or generate discomfort for the aircraft crew and passengers. Hence, there is a need for instability simulation and prediction methods that can be used as early as the design stage. At this stage, finite element models are available, but their sizes are prohibitive as far as vibration-level prediction is concerned, thus requiring model reduction. This paper presents a comparative study between several modal reduction methods, among them the well-known Craig–Bampton method. The reference model to be reduced is a full brake system finite element model. The system stability is assessed by means of the classical complex eigenvalue analysis. Convergence of the implemented reduction strategies is studied. Double modal synthesis is implemented, and an improved version is introduced. They appear to be efficient model reduction strategies for application to squeal prediction. By reducing all the system’s degrees of freedom on several sets of generalized coordinates, an excellent compromise between system size and precision can be found.

Investigation of shear failure in airport asphalt pavements under aircraft ground manoeuvring

This study aimed to investigate the effect of aircraft ground manoeuvring operations on shear failure potential of airfield asphalt pavements using the multi-axial stress state criteria. A numerical modelling study was conducted to characterise the stress state in the asphalt layer using an advanced three-dimensional (3-D) finite element (FE) model that has been validated in previous studies. The complex tyre–pavement interactions were characterised with non-uniform distributions of tyre–pavement contact stresses at vertical and tangential directions. Different tyre rolling conditions caused by aircraft ground manoeuvring during landing were simulated including free rolling, full-braking, and turning. The effects of takeoff weight and operating speed were also considered in the analysis. The multi-axial stress states in the bulk asphalt material and at the asphalt layer interface were analysed by means of the Mohr–Coulomb failure criteria in a normal-shear stress plane. The results emphasised the importance of tyre–pavement interaction and considering multi-axial stress state criterion for analysis of pavement shear failure. Aircraft braking or turning significantly increases the shear failure potential in the bulk material and at the asphalt layer interface due to the tangential stresses applied on pavement surface. The effects of aircraft weight and operating speed on pavement shear failure were limited compared to aircraft manoeuvring. The analysis of stress states in the asphalt layer sheds light on the requirement of shear strength and selection of laboratory tests for evaluation of shear failure potential at airfield asphalt pavements.

Shear stresses in an asphalt surface under various aircraft braking conditions

Aircraft braking forces have increased in the past and will continue to increase in the future. This has resulted in instances of shear related distress in asphalt runway surfaces. The shear stresses transferred from braking tyres to the pavement surface can initiate failures of poorly bonded interfaces. Shear creep deformation within the mix can also occur. Octahedral shear stress (OSS) has been recommended as an indicator of asphalt distress. OSS is unaffected by the geometry of loading and reference coordinate system. In this research, the peak surface forces in three dimensions were calculated. Stresses through the surface layer were then calculated using mePADS/GAMES software. The calculated stresses in the surface layer were compared under various braking conditions. The OSS was used as the primary basis for these comparisons.The maximum calculated OSS induced by a heavy braking truck was only 53% of that for the aircraft during only moderate braking. Contrary to expectation, the peak shear stress under the leading edge of the tyre did not increase significantly with increased aircraft braking effort. Analysis of the shear stress distributions, however, identified a significant change with increased braking effort. For non-braking aircraft, a zone of near-zero shear stress was found under the central portion of the tyre. As the horizontal surface force increased, this became a zone of near-constant shear stress. Observed differences in field performance of nominally identical asphalt in landing/braking zones of an airport were not explained by the peak OSS values calculated. It was, however, concluded that the near-steady shear state under a passing tyre during aircraft braking could explain different asphalt responses in the field. This conclusion was consistent with the observed nature of such failures, which are creep related, rather than the result of conventional slip circle shear. It was suggested that the presence of shear related failures only in the braking area would be indicative of shear creep deformation within the mix rather than delamination at the surface interface.

Multi-criteria failure mode effects and criticality analysis method: a comparative case study on aircraft braking system

The Department of the USA's Army published technical manual TM 5-698-4 to create a new failure mode effects and criticality analysis (FMECA) method, since the formal military specifications and standards MIL-STD-1629A was cancelled. However, the design processes of the two-phase product do not take the most appropriate corrective measures to eliminate the product risks in the first design phase. Thus, the risk priority number (RPN) and criticality analysis (CA) methods have serious flaws from a technical perspective which are still widely used and misleading in the related FMECA handbook and instruction manual. This paper uses the maximal entropy ordered weighted geometric averaging (ME-OWGA) operator to obtain the optimal weighting vector, which calculates FMECA values in one-phase and moreover circumvents the difficulties of mathematical operators. A fighter aircraft braking system is used as a case study to illustrate the proposed method, which compares the proposed approach with the RPN and CA methods. The results indicate that the proposed method can efficiently shorten the design process and more accurately calculate than MIL-STD-1629A, TM 5-698-4, FMECA handbook and other equivalent instruction manuals.

Shear creep response of an airport asphalt mastic

Two runways were resurfaced with 50–60 mm of typical airport asphalt at the same airport. One runway surface performed well while the other exhibited a lack of resistance to cyclic shear stress under heavy aircraft braking. Both runways had the same hydrated lime filler and coarse aggregate source. The fine aggregate (dust) used to manufacture the two runway surfaces was obtained from two different basalt quarries. The dust associated with the poorly performing asphalt contained a potentially detrimental clay mineral (Hisingerite). It was subsequently determined that the crude oil used to manufacture the feedstock for the acid-modified binder also changed at the transition from one runway to the other. The changes in dust and binder were confounded. A combination of viscosity testing and performance-based multiple stress creep recovery (MSCR) testing determined that the two runway binders responded significantly differently to shear stress and aged differently with sample storage time. The differences were magnified at higher temperatures. Further, mastic samples were manufactured from binder associated with both feedstocks, in combination with dust from both quarries. MSCR testing of mastic indicated that the dust containing significant Hisingerite had no adverse impact on the mastic response to shear stress. The change in binder feedstock was concluded to be the root cause of the lack of resistance to cyclic shear stress observed in one runway surface. This occurred despite all batches of binder meeting the viscosity-based Australian specification for paving grade bitumen. The specification has no mechanism to prevent similar changes in bitumen feedstock affecting airport bitumen performance in the future. Incorporating performance-based testing in the Australian bitumen specification is recommended.

Two-Dimensional Thermal Model of Asperity Heating in a Disk Pair in Dry Friction Between Two Rough Surfaces

In this paper, a formulation for the rate of heat generation due to the contact of one asperity with asperities on a second surface is proposed. A statistical approach is used to obtain the heat generation rate due to one asperity and employed to develop the equation for generation of heat rate between two rough surfaces. This heat rate formulation between the two rough surfaces has been incorporated into the 2D lumped parameter model of disk pair in dry friction developed by Elhomani and Farhang (2010, “A 2D Lumped Parameter Model for Prediction of Temperature in C/C Composite Disk Pair in Dry Friction Contact,” ASME J. Therm. Sci. Eng. Appl., 2(2), p. 021001). In this paper, the disk brake is viewed as consisting of three main regions: (1) the surface contact, (2) the friction interface, and (3) the bulk. Both surfaces of the disk brake are subjected to frictional heating. This model is considered to be a necessary step for simulating the aircraft braking system that consists of a stack of multiple disks.

Energy method of safe aircraft braking forecasting

The method of forecasting reachability of a terminal state at modes of regular or emergency braking of the aircraft is developed. The method is based on the energy approach to flight control. To improve forecast reliability, the correction of forecasting algorithms is proposed. Applicability of an early warning or notice to a pilot on possibility of safe braking within the runway is proved by simulation results. It is to be noted that such messages can improve pilot's situational awareness and thus decrease probability of false operations of the aircrew.