Motor Current Signature Analysis is a critical non-invasive technique for detecting mechanical and electrical faults in induction motors. Traditional MCSA requires expert knowledge to interpret frequency spectrum patterns and identify characteristic fault signatures. This paper explores the application of Large Language Models as intelligent diagnostic assistants for MCSA interpretation. Modern LLMs can analyze motor current spectra, identify fault-related frequency components, and classify common motor faults including bearing defects, broken rotor bars, eccentricity, and misalignment. The system accepts frequency spectrum images with motor specifications, then applies reasoning to detect anomalies based on established diagnostic criteria. Preliminary results on five representative cases suggest that LLMs can identify characteristic fault frequencies, handle ambiguous fault conditions, and provide diagnostic explanations consistent with established MCSA criteria. This approach has potential to democratize MCSA by making expert-level diagnostic capabilities accessible to maintenance personnel with limited MCSA experience, while also serving as a decision support tool for experienced analysts. The integration of LLMs into predictive maintenance workflows represents a promising direction for industrial diagnostics.

This paper presents a novel approach to aircraft piston engine diagnostics utilizing a Large Language Model (LLM) enhanced with domain-specific knowledge. The methodology combines traditional engine monitoring data analysis with advanced natural language processing capabilities to identify and diagnose engine anomalies. The system processes real-time engine parameters including Cylinder Head Temperatures (CHTs), Exhaust Gas Temperatures (EGTs), engine RPM, Fuel Flow (FF), and Turbine Inlet Temperature (TIT) from engine monitoring systems. The LLM's diagnostic capabilities are augmented through the integration of expert knowledge, implemented as a comprehensive set of IF-THEN rules and detailed textual descriptions of common engine fault patterns extracted from maintenance documentation. This hybrid approach enables the system to leverage both structured operational data and unstructured maintenance expertise to provide accurate fault diagnostics. The methodology shows particular promise in detecting subtle fault patterns that may be missed by conventional monitoring approaches, potentially enabling more proactive maintenance interventions and enhanced flight safety.

This paper is a very brief introduction to the field of active noise control. The concept of active noise control based on destructive interference of sounds is presented. The need for high amplitude and phase accuracy of canceling sound for efficient cancellation is shown. Considered is the possibility of noise cancellation in open and closed space. Quiet zone formed in the local noise cancellation related to the noise wavelength is illustrated. Most important approaches used for active noise control such as the feedforward, feedback and hybrid method are laid out. Adaptive feedforward and feedback structures based on adaptive filtering are outlined considering the influence of secondary path transfer function and acoustic feedback. Suitability of particular methods for different sound characteristics like broadband and narrowband noise and availability or absence of the reference signal is considered. Synchronized waveform synthesis is also presented as a solution for active control of periodic noise commonly produced by rotating machinery. General directions for digital implementations such as choice of sampling rate, adaptive filters length, computational cost, circuits for pre-filtering and post-filtering of reference, error, and secondary signal are given. Some typical applications are listed.

Active noise control of periodic sounds, as commonly produced by rotating machinery, can be efficiently implemented using a synchronized waveform generator that produces a secondary signal necessary for noise cancellation. Synchronization of synthesized waveform is achieved by the use of reference tacho signal picked up by the magnetic or optical sensor. Waveform adaptation is performed in accordance with the residual noise signal after noise cancellation. Such approach for active noise control works well when a spectrum of offending noise is not changing much. However, during initial machine spool up, varying load and final spool down significant adaptability from waveform synthesizer is required to counteract changes in machine noise. In this paper, methods for improving convergence and tracking properties of waveform generator are presented and analyzed. An adaptive coefficient of waveform generator is modified in accordance to elapsed time during startup, varying frequency of the reference tacho signal and residual noise level. Results of simulations with different noise spectrum corresponding to various machinery rotational speeds are included.

Modern engine monitors provide vast amounts of data obtained from aircraft piston engines. Most important parameters are Cylinder Head Temperatures (CHTs) and Exhaust Gas Temperatures (EGTs) that are available for each engine cylinder. A CHT-EGT trajectory is formed from successive CHT-EGT pairs present in a CHT-EGT scatter plot. The short term CHT-EGT trajectory captures short term dynamics of engine temperatures and can be used for its visualization. By comparing temperatures of the individual cylinders, under the assumption of similarity of operating temperatures of individual cylinders in a normal engine, abnormalities in engine operation can be detected. The method based on the comparison of short term CHT-EGT trajectories can be used to detect abnormalities during dynamic engine operation. During static engine operation, the CHT-EGT trajectory should shrink to a small area, and this can also be used to detect engine abnormalities.

Aircraft rotors are sources of high levels of noise. Noise levels produced by helicopters and large drones are a great nuisance in urban areas. The theoretical concept of Active Noise Control (ANC) applied to aircraft rotors is presented. Concept of ANC for a ducted rotor is extended to an open rotor. Later uses ultrasonic arrays placed around the truncated cone as secondary sources of ultrasound beams of high directivity driven by the multichannel control device to diminish noise levels produced by the rotor. Amplitude modulated adjacent ultrasound beams originating from the ultrasonic arrays produce a rotational acoustic field that rotates together with the rotor. Noise cancelation by modulated ultrasound beams directed to the rotor targets the position of the dominant sources of rotor noise, i.e., rotor tips.

Cymatics is a visual representation of sound in form of geometric patterns. It is accomplished by a tonoscope device. In most implementations, dispersed fine particulate matter is placed on a horizontal metal plate (Chladni plate) that is excited by frequencies present in the sound under analysis. Sound, resonances, standing waves and nodes appear as interesting symmetric geometric patterns. Instead of physical implementation, software implementation of the tonoscope can also be used. In this paper noise of various aircraft engines is analyzed. Developed patterns could be potentially used for early detection of impending faults.

Limit checking is very simple and intuitive method that can be applied for fault detection. Concept and variants of limit checking are briefly reviewed in this paper. This includes limit checking of absolute values, trend checking, fixed and adaptive thresholds, use of hysteresis and change detection.

Modern aircraft piston engine monitor collects large amounts of data representing engine parameters. Data acquired during each flight is logged to a file. From the logs acquired during numerous previous flights a database of a healthy engine is formed containing feature vectors with selected engine parameters. Due to high speed processing of even modest microcontrollers, new feature vectors acquired during a flight can be compared in real time to all previous feature vectors stored in the database. Any significant discrepancy may indicate a problem in engine operation or engine fault. Such detection may alert a pilot and help prevent engine failure, partial loss of engine power or unplanned in-flight engine shutdown.

A recent trend in electric cars introduces new problem due to their silent movement. Electric cars are much quieter than conventional cars equipped with internal combustion engines. This lack of noise poses a danger to other road users. To increase the safety of pedestrians, under certain conditions, artificial noise generators must be used, as required by EU regulations. Car engine noise synthesis is proposed that combines sample based synthesis and envelope scaling dependent on engine rotational speed.

Fountains are appealing visual and acoustic additions to outdoor and indoor spaces. By pouring or jetting water, fountains produce pleasant and tranquil sounds of flowing water and water bubbles. The sound of the fountain depends on its water feature style that produces sound with the particular sound level, frequency and temporal envelope characteristics. In this paper, analysis of frequency spectrum and variations in a temporal envelope of the fountain sound are performed. Methods for the synthesis of fountain sound are outlined, including physical modeling synthesis and conventional sampling synthesis using prerecorded sound waveforms.

The majority of general aviation aircrafts use piston engines that are considerably less reliable than turbine engines. Most problems of aircraft piston engines are reflected in engine temperature parameters like cylinder head temperature (CHT) and exhaust gas temperature (EGT) that are recorded by engine monitor. Three approaches for detection of engine problems are presented. Many problems may be detected by comparison of statistical distributions of CHTs and EGTs from individual cylinders. Incipient exhaust valve failure may be detected from temporal EGT pattern containing low frequency fluctuations. The life of the exhaust valve depends on its operating temperature. Because EGT is the major contributor to the overheating of the exhaust valve and its cooling mostly depends on the CHT, the remaining life of exhaust valve may be assessed from cumulative sum of EGT and CHT during the period of use.

Active noise control algorithms for real world applications regularly use some kind of digital filtering and adaptation to compensate for the influence of the secondary path. Such is the FxLMS algorithm with techniques for off-line and on-line estimation of the secondary path, suitable both for broadband and narrowband noise. When silencing periodic noise using waveform synthesis, much simplified solution can be used. Instead of a long adaptive filter, a simple delay can be used. After initial off-line calibration, delay values are stored in a lookup table. These values are used later instead of adaptive filter and may change with the frequency of repeating waveform. It is a simple and intuitive solution that poses some restriction on phase response of used secondary source. Due to the low computational requirements it is suitable for implementation using simple and low cost microcontroller.

Unmanned aerial vehicles (UAVs) like drones (quadcopters, hexacopters, octocopters etc.) can be a source of a significant acoustic noise. High noise makes them less suitable for use in densely populated urban areas, particularly during take-off, landing and low level flight, due to the noise annoyance. This paper reviews methods and proposes some concepts for attenuation of UAV noise. Both passive and active solutions are considered. Solutions with piston engine silencer, Q-tip propeller, more propeller blades, absorptive and reflective barrier, ducted propeller, sound absorbing ducts, synchrophaser, multichannel active noise cancellation (ANC) system with secondary sources circularly arranged around the propeller and the system with magnetically excited propeller blades are mentioned.

Aircraft piston engine can be monitored using an advanced graphic engine monitor. Such engine monitor can supply a large amount of data containing evolution of engine parameters through the time. Analysis of a vast amount of multidimensional temporal data by a self-organizing map may aid in data visualization, but also in detection of engine parameter deviations from normality indicating potential problems in operation of aircraft piston engine. For determination of engine parameter space that corresponds to normal engine operation quantization error of the self-organizing map is used.

As a particular type of artificial neural networks, self-organizing maps (SOMs) are trained using an unsupervised, competitive learning to produce a low-dimensional, discretized representation of the input space of the training samples, called a feature map. Such a map retains principle features of the input data. Self-organizing maps are known for its clustering, visualization and classification capabilities. In this brief review paper basic tenets, including motivation, architecture, math description and applications are reviewed.

Beginnings in the field of active noise control date from 1930s. From these pioneer attempts great deal of progress has been achieved. In this brief review paper advances from simple fixed analog systems, manually adaptive analog systems, acoustic feedback neutralization, fully adaptive digital systems with secondary path modeling and multichannel systems are briefly presented. Applications of active noise control in closed and open space, industrial and automotive applications, as well as active noise canceling headphones and new solutions with smart materials are also briefly mentioned.

The paper deals with active noise control system for the cabin of a light aircraft. Basic system uses coherent averaging method of the residual error signal to produce signal that drives secondary source. Advanced versions of this system use a-priori information about noise waveform and adaptation process begins with the assumed waveform (sinus signal of adequate amplitude, phase and frequency or even low pass ˇltered referent noise signal). After testing single-channel system, achieved noise suppression is veriˇed with additional simulation considering measured acoustic characteristics of real aircraft cabin (characterized by impulse responses). System could be extended to multichannel version of type SIMO (Single Input Multiple Output) where the same tacho/referent signal after adequate delay (acoustic propagation of the noise signal through the cabin) drives eight single-channel systems connected with multiple gain-delay combinations to reduce crosstalk between individual channels.

Immersive virtual environments necessary for realistic flight simulations need wide view visual systems that cover large horizontal visual angle and consist of multiple video channels. Methods for achieving this task in flight simulator are presented: use of displays and projectors, most common types of visual systems, use of multiple graphics cards and multihead graphic cards, single graphic card with graphic expansion modules and surround display using PC clusters. Integration of visual system with rest of simulator is described. Implementation of flight simulator with three channel visual system on PC cluster is described.

Data centers with its numerous servers, network switches, routers and air conditioning equipment produce significant noise that influences work and communication of maintenance staff. Noise levels and spectrum within a data center are measured and analyzed. Daily and weekly variations of noise levels are also captured. From measured noise levels and spectrum speech intelligibility measures are calculated and communication distances within a data center are determined. The need for noise protection and methods for noise reduction are considered.