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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. [ABSTRACT FROM AUTHOR]

Accurately measuring the cogging torque, hysteresis torque, and iron losses of permanent magnet (PM) motors is a challenging task. This is especially true for sub-fractional horsepower (SFHP) variants used, e.g., in auxiliary drives for automotive fan and pump applications. Their cogging torque and hysteresis torque peak values are often in the sub-milli-Newton meter range, causing conventional measuring methods and devices to fail as especially friction impedes the measurement significantly. Moreover, their iron losses are hard to determine and usually merely estimated in the literature. This article presents an unconventional rheometer-based method to determine both 1) the cogging torque and hysteresis torque of SFHP PM motors and 2) their iron losses by evaluating the observed offset torque. Two SFHP outer-rotor PM motor topologies for fan applications are analyzed, i.e., a claw-pole motor and a salient-pole motor. The results show that, with the proposed setup, settings, and evaluation, a rheometer can successfully be used to determine the cogging torque and hysteresis torque waveforms in the sub-milli-Newton meter range and the iron losses of SFHP motors, both with excellent accuracy. [ABSTRACT FROM AUTHOR]

Tribological tests are adopted to estimate the kinetic friction coefficient (COF) of the material of interest according to the American Society for Testing and Materials (ASTM) standard. Typically, for the measurement process, several replicas, as well as a postprocessing data treatment, are necessary to take into account the observed casual variability of the measurand. This article describes a statistical approach aiming to highlight the running-in phase and the most significant time intervals during the steady-state for each test replica. A two-steps procedure based on the adoption of the bootstrap method allows the automatic detection of the running-in time interval and the outlier filtering of the steady-state. Experimental activity has been carried out by performing multiple tests through the ball-on-flat tribometer in order to verify the improvement allowed by the authors’ proposal about the dry friction COF measurement in terms of both accuracy and repeatability. [ABSTRACT FROM AUTHOR]

The melting erosion law of the contact interface between armature and rails on the electromagnetic (EM) railgun is one of the key factors affecting the launching performance. In order to study the melting erosion law on the contact interface of a multiturn series–parallel (MSP) railgun, an EM structure thermal multiphysical field coupling model is built, and the armature velocity, contact force, and temperature of contact interface under different current peak values and shrink ranges are analyzed. Besides, the related verification experiments are carried out, and the melting erosion law of the contact interface is obtained. The results of simulations and experiments show the following conclusions: First, during the launching, the contact force between armature and rails varies with current fluctuation. Second, the friction heat power varies directly with the contact force, but Joule thermal power caused by contact resistance varies inversely with the contact force. Third, the ambient temperature of the sliding contact interface can be further improved by reasonable design of armature shrink range. Fourth, due to the inevitable wear during sliding, the melting area of the armature contact surface gradually transfers from the initial contact area to the tail. The above-mentioned conclusions can provide a technical reference for the high-speed experimental study of MSP railgun. [ABSTRACT FROM AUTHOR]

Real-time classification of road surface conditions is very important for the control of a vehicle properly within its handling limits. There have been numerous attempts to estimate the road surface conditions, but there is a plenty of room for improvement, since most of the estimation methods have some robustness issues in real-world applications. The method proposed in this paper utilizes the relationship between the road surface condition and the tire cornering stiffness. Since the tire cornering stiffness varies significantly depending on the road surface condition, it can be estimated out of the tire cornering stiffness, which is measured accurately at the early state of wheel slip. In this study, normalized tire cornering stiffnesses are estimated in real time, exploiting the fact that production vehicles are generally built to show some understeering characteristics. The proposed method compares the front and rear wheel slips simultaneously, unlike other studies that focus on individual wheel slip. In this way, estimation of unmeasurable major vehicle states such as wheel sideslip angle and absolute vehicle speed can be eliminated from the entire algorithm. The experimental results show satisfactory estimates of less than 10% error and confirm the feasibility of the proposed algorithm in production vehicles without exotic extra sensors. [ABSTRACT FROM AUTHOR]