Rotation Frequency Research Articles

Design of hydraulic motors with rotary shaft movement for driving working equipment in modern machines

The object of research is the processes in hydraulic motors based on power cylinders, designed to drive the shaft of the working equipment in modern machines into rotational motion. When using standard motors, a problem arises relating to the need to introduce additional devices into the structure of the mechanisms of modern machines. Such devices are aimed at matching the rotation frequency of the motor shaft with the rotation shaft of the working equipment of these machines. Such a device is a reducer, the use of which leads to the appearance of a number of disadvantages. Their elimination is achieved by using the results of this study. The reported results differ from standard motors that are mass-produced, in that, based on research, motors with a rotation frequency of its shaft in the range from zero to two hundred and more revolutions per minute are proposed, which is not realized by known motors. This testifies to the construction of motors based on power cylinders, which make it possible to realize this range of rotation frequencies of its shaft. The special and distinctive features of the results are based on the application of the principle of disintegration of motor elements into two functional components. One of them includes power cylinders with a crankshaft, and the second one includes the distribution system of the working fluid. The motor implementation went through the stages of designing computer and physical models and devising schematic solutions. Calculation dependences were obtained to determine the main design parameters, according to which the motor was manufactured in the form of a full-scale sample. The scope and conditions of practical use refer to machines with working equipment capable of functioning under a mode with a low rotation frequency and a significant torque on the motor shaft

Devising a calculation method for modern structures of current-conducting elements in large electric machines in a three-dimensional statement

The jumpers of rotor pole-to-pole connections are highly stressed elements in a hydraulic generator structure. These assemblies often fail due to deformation that exceeds the size of an air gap. Existing methods do not take into account the thermal component and attempts to improve the design are not based on mathematical models that make it possible to perform calculations with an accuracy of more than 50 %. The method devised in this work makes it possible to obtain boundary conditions of the third kind on the basis of three-dimensional mathematical modeling of the ventilation system of the hydraulic unit without simplifications. The method accuracy is explained by taking into account the spatial thermal component. The heat transfer coefficient determined by this method in the pole-to-pole connections area was ~250 W/(m2·K). Using FEM, mathematical modeling of the thermal stress state of pole-to-pole connections was carried out, taking into account mechanical and thermal factors. This made it possible to design the improved connection structure with additional fastening elements, which make it possible to reduce the displacement to 0.03 mm, and the stress to 53 MPa at the rotor rotation frequency of 880 rpm. This design makes it possible to enable reliable operation of the hydraulic unit under the condition of increasing the rotor rotation frequency to overspeed with disconnected combinatorial dependence, provided that the actual stresses are 0.95 % of the material yield strength. The convergence of the values obtained by the proposed method and by the HSS method exceeded 99 %. The practical result is the proposals for the hydraulic generator design modernization

Substantiation of the Efficiency of Processing Flax Straw of Different Quality in the Modernized Machine MTOF-1M

The proposals are presented for upgrading the singleprocess scutching-and-breaking machine MTOF-1L to MTOF-1M. It has been analyzed how the characteristics of scutched, short and single-type flax are influenced by the processing time and the rotation frequency of scutching drums of the MTOF-1M in the line for agricultural enterprises, rational modes of the operation of the machine are determined. The line for primary processing of flax straw of various properties for small enterprises is substantiated.

Rotating dipole and quadrupole quantum droplets in binary Bose-Einstein condensates

Quantum droplets (QDs) are self-trapped modes stabilized by the Lee-Huang-Yang correction to the mean-field Hamiltonian of binary atomic Bose-Einstein condensates. The existence and stability of quiescent and rotating dipole-shaped and vortex QDs with vorticity S=1 (DQDs and VQDs, respectively) are numerically studied in the framework of the accordingly modified two-component system. The rotating DQDs trapped in an annular potential are built of two crescentlike components, stretching along the azimuthal direction with the increase of the rotation frequency. Rotating quadrupole QDs (QQDs) bifurcate from the VQDs with S=2. Above a certain rotation frequency, they transform back into VQDs with a flat-top shape. Rotating DQDs and QQDs are stable in a broad interval of values of the chemical potential. The results provide the first example of stable modes which are intermediate states between the rotating DQDs and QQDs on the one hand and VQDs on the other. Published by the American Physical Society 2024

Localized rail third-order bending mode causes high-order polygonization of high-speed train wheels

The formation mechanism of high-order (mainly 18 ∼ 23) polygonization of high-speed train wheels has been debated for over a decade. Currently, researchers believe that the mechanisms leading to the high-order polygonization of high-speed train wheels mainly include: (A) vibration of bogie components, (B) self-excited vibration of wheel-rail friction, (C) third-order bending (B3) modal vibration of a segment of localized rail constrained by a bogie, etc. Of these, mechanism C was previously proposed by our team and has been insisted on until now, although it is highly controversial. To further prove the plausibility of mechanism C, through rail modal tests, vehicle tracking tests, and dynamics simulation analyses, this paper systematically proves that (1) the rail B3 mode can induce resonance of the wheel-rail system, which is the fundamental factor causing the high-order polygonization of high-speed train wheels, and (2) there is no significant frequency shift between the vibration frequency of the excited rail B3 mode and the passing frequency of the formed polygonal wheel, with an extreme difference being less than the wheel rotation frequency.

Investigation of H∞$$ {\mathcal{H}}_{\infty } $$‐Tuned Individual Pitch Control for Wind Turbines

ABSTRACTLarge wind turbines experience amplified asymmetrical loads at particular harmonics of the rotational frequency. Individual pitch control (IPC) has emerged as a potential controls solution to this problem. control, which facilitates robust, multivariable controller synthesis in the frequency domain, is a candidate approach to IPC design for several reasons. First, the objectives of asymmetrical load attenuation can be readily described in the frequency domain. Second, the IPC signals and loads in orthogonal directions are known to be coupled, which necessitates a multivariable controller approach. Third, synthesis is a method that can explicitly impose constraints on the robustness of the closed‐loop system. A downside of IPC is the significant increase in blade‐pitch travel incurred, which introduces additional loading on the blade‐pitch bearings over time. We investigate strategies to constrain the blade‐pitch travel in the controller tuning procedure. A comprehensive study is thus presented for a range of ‐synthesized IPCs to attenuate asymmetrical loads on large rotors at harmonics of the rotational frequency while reducing blade‐pitch travel. All developed controllers are validated and compared using a 25‐MW fixed‐bottom offshore wind turbine model via (a) linear analysis of the response of the closed‐loop system to input and output disturbances, (b) nonlinear analysis in terms of structural load power spectra and damage‐equivalent loads (DELs), and (c) the actuator duty cycle (ADC) of the blade‐pitch actuator.

Pulsations of Three Rapidly Oscillating Ap Stars TIC 96315731, TIC 72392575, and TIC 318007796

We analyze the frequencies of three known roAp stars, TIC 96315731, TIC 72392575, and TIC 318007796, using the light curves from the Transiting Exoplanet Survey Satellite. For TIC 96315731, the rotational and pulsational frequencies are 0.1498360 day−1 and 165.2609 day−1, respectively. In the case of TIC 72392575, the rotational frequency is 0.25551 day−1. We detect a quintuplet of pulsation frequencies with a center frequency of 135.9233 day−1, along with two signals within the second pair of rotational sidelobes of the quintuplet separated by the rotation frequency. These two signals may correspond to the frequencies of a dipole mode. In TIC 318007796, the rotational and pulsational frequencies are 0.2475021 day−1, 192.73995 day−1, and 196.33065 day−1, respectively. Based on the oblique pulsator model, we calculate the rotation inclination i and magnetic obliquity angle β for the stars, which provide the geometry of the pulsation modes. Combining the phases of the frequency quintuplets, the pulsation amplitude and phase modulation curves, and the results of spherical harmonic decomposition, we conclude that the pulsation modes of frequency quintuplets in TIC 96315731, TIC 72392575, and TIC 318007796 correspond to distorted dipole mode, distorted quadrupole mode, and distorted dipole mode, respectively.

Lagrangian Versus Eulerian Spectral Estimates of Surface Kinetic Energy Over the Global Ocean

AbstractIn this study, we conducted a novel massive Lagrangian simulation experiment based on a global 1/48° tide‐resolving numerical simulation of the ocean circulation. This first‐time twin experiment enables a comparison between Eulerian (fixed‐point) and Lagrangian (along‐flow) estimates of kinetic energy (KE) across the global ocean, and the quantification of systematic differences between both types of estimations. This comparison represents an important step forward for the mapping of upper ocean high‐frequency variability from Lagrangian observations of the Global Drifter Program. Eulerian KE rotary frequency spectra and band‐integrated energy levels (e.g., tidal and near‐inertial) serve as references and are compared to Lagrangian estimates. Our analysis reveals that, except for the near‐inertial band, Lagrangian velocity spectra are systematically smoother, for example, with wider and lower spectral peaks compared to Eulerian counterparts. On average, Lagrangian KE levels derived from spectral band integrations tend to underestimate Eulerian KE levels at low‐frequency and tidal bands, especially in regions with strong low‐frequency KE. Better agreement between Lagrangian and Eulerian low‐frequency and tidal KE levels is generally found in regions with weak low‐frequency KE and/or convergent surface circulation, where Lagrangian particles tend to accumulate. Conversely, Lagrangian and Eulerian near‐inertial spectra and energy levels are comparable. Our results demonstrate that Lagrangian estimates may provide a distorted view of low‐frequency and tidal variance. To accurately map near‐surface velocity climatology at these frequencies from drifter database, conversion methods accounting for the Lagrangian bias need to be developed.

Experimental study on upstream pressure characteristics of rotating detonation engine with methane and oxygen-enriched air

The interaction mechanism between the rotating detonation engine (RDE) and its upstream is one key issue that needs to be explored when considering its application. In this study, experimental tests with methane and 50% oxygen-enriched air are conducted to investigate the relationship between upstream pressure characteristics and the detonation wave. As a result of operational considerations, a hollow chamber and a rear ignitor are used and the initiation process is discussed. Upstream pressure characteristics are analyzed under varied injection pressures and equivalence ratios. Stable modes including single-wave and double-wave modes are recorded in most cases. Notably, two unstable modes are also captured at low injection pressure in which the detonation quenches quickly. The results highlight that significant feedback pressure pulsations synchronize with the rotation frequency of detonation waves after ignition due to the upstream oblique shock wave (UOSW). But the inherent frequency of injection should also be emphasized at elevated injection pressure. The detonation wave can also cause injection blockage, particularly at low injection pressure, leading to the bifurcation of unstable mode. Such unstable is attributed to an inadequate upstream pressure increase after ignition, which hinders the injection reconstruction. Further analysis reveals that higher injection pressures or lower equivalence ratios diminish the differential between the detonation wave and upstream pressure, and consequently, the pulsation amplitude. An increase in the detonation wave number can also reduce the pulsation amplitude, which can even be lower than 10% in a double-wave mode. The results are beneficial for integrating RDE and its upstream components.

Rydberg-Induced Topological Solitons in Three-Dimensional Rotation Spin–Orbit-Coupled Bose–Einstein Condensates

Abstract We introduce a novel approach for generating stable three-dimensional (3D) spatiotemporal solitons (SSs) within a rotating Bose-Einstein Condensates, incorporating Spin-Orbit-Coupling (SOC), a weakly anharmonic potential and cold Rydberg atoms. This intricate system facilitates the emergence of quasi-stable 3D SSs with topological charges |m| ≤ 3 in two spinor components, potentially exhibiting diverse spatial configurations. Our findings reveal that the Rydberg long-range interaction, spin-orbit coupling, and rotational angular frequency exert significant influence on the domains of existence and stability of these solitons. Notably, the Rydberg interaction contributes to a reduction in the norm of topological solitons, while the SOC plays a key role in stabilizing the SSs with finite topological charges. This research of SSs exhibit potential applications in precision measurement, quantum information processing, and other advanced technologies.

Experimental investigation on aerodynamic noise of a small-scale multi-blade centrifugal fan

In this study, the aerodynamic noise of a small-scale centrifugal fan was experimentally investigated using acoustic testing techniques and time-resolved stereoscopic particle image velocimetry (SPIV). During the acoustic experiments, both far-field noise and near-field pressure fluctuations of the test fan were measured. The overall far-field noise towards the fan inlet side was found to be higher than that of the back side. The pressure fluctuations on the fan upper casing exceeded those on the side wall due to the uncontracted volute tongue, indicating pronounced flow-to-wall interactions. Moreover, based on a simultaneous measurement, the coherence between the near-field pressure fluctuations and far-field noise highlighted the significant contributions of impeller rotation to noise radiation. SPIV measurements uncovered the time-averaged and transient flow fields at the fan's inlet and outlet. The time-averaged results demonstrated the concentrated inlet flow and outlet flow separation, leading to high flow unsteadiness. Transient flow fields displayed an asymmetric jet-wake region characterized by both quasi-steady flow and rotational flow behaviours. The instantaneous flow results were analyzed using the dynamic mode decomposition (DMD) method, which clearly recognized the jet-wake patterns with frequencies corresponding to the rotational frequency. The observed consistency in frequency characteristics among noise, pressure fluctuations, and unsteady flow affirms that flow dynamics are crucial to the primary noise mechanisms.

Curved vortex surfaces in four-dimensional superfluids. I. Unequal-frequency double rotations

The study of superfluid quantum vortices has long been an important area of research, with previous work naturally focusing on two-dimensional and three-dimensional systems, where rotation stabilizes point vortices and line vortices respectively. Interestingly, this physics generalizes for a hypothetical four-dimensional (4D) superfluid to include vortex planes, which can have a much richer phenomenology. In this paper we study the possibility of skewed and curved vortex planes, which have no direct analog in lower dimensions. By analytically and numerically studying the 4D Gross-Pitaevskii equation, we show that such vortex surfaces can be stabilized and favored by double rotation with unequal rotation frequencies. Our work raises open questions for further research into the physics of these vortex surfaces and suggests interesting future extensions to tilted vortex surfaces under equal-frequency double rotation and to more realistic 4D models. Published by the American Physical Society 2024

Efficient vibration analysis system using empirical mode decomposition residual signal and multi-axis data

The empirical mode decomposition (EMD) method is a technique that recursively decomposes an input signal into intrinsic mode functions (IMFs) by residual signals, primarily for identifying desirable features. The suggested algorithm observes the residual signal instead of the IMF, which lowers the computing load. The study introduces a new method for detecting bearing faults by enhancing signal extraction from sensor data using EMD and multi-axis feature extraction. This method streamlines the process by filtering out high-frequency noise and correlating residual signal information with analysis. The approach also enhances the signal-to-noise ratio (SNR) and feature signature identification using digital signal processing (DSP) techniques. The algorithm for vibration data analysis is tested for bearing failures, identifying shaft frequency and inner race bearing faults, which can be implemented in parallel. For the inner race fault bearing analysis, two-level EMD with a residual signal generates output similar to five-iteration EMD, saving 60% of computations. The use of spectral multiplication to multi-axis data processing produced a rise in the SNR of 18.32 dB to 20.92 dB for Y-axis and X-axis input, respectively. When compared to the single-axis IMF data computation, 20% fewer iterations are needed overall. A single-level EMD is adequate for calculating the rotational frequency of a healthy bearing. For the Y- and X-axis input, multi-axis analysis increases SNR by 10.68 dB and 13.14 dB, accordingly. This comprehensive strategy reduces computational complexity, improves fault detection accuracy, and minimizes noise impact, making it a promising solution for bearing fault detection.

Robust detection of a rotational Doppler shift with randomly fluctuated light.

The complex external environment, such as obstruction and turbulence, poses significant limitations on the applications of rotational Doppler detection. The active manipulation of randomly fluctuated light has been proven effective in mitigating external environmental perturbations. Here, as an example, a partially coherent source with petal-like focal (or far) field distribution is constructed specifically for detecting rotational Doppler frequency shifts. The experiment involved conducting rotational Doppler detection under obstruction or turbulence conditions, and the results are compared with the fully coherent counterpart. The results demonstrate that the use of a partially coherent source can address the frequency-shift broadening problem due to the obstruction-induced beam information loss and mitigate it due to the turbulence-induced beam misalignment. These advantages make the proposed approach applicable to velocity metrology in complex environments.

Numerical Investigation on the Influence of Continuous Rotating Backpropagation Pressure Wave on Turbine Performance

Abstract Researches have shown that the use of a continuous detonation afterburner can improve the propulsion performance of aero engine. However, backpropagation pressure waves (BPW) generated by the pressure gain of detonation will affect the internal flow and performance of turbine. This article simulates BPW through a custom function, and investigates the effects of BPW amplitude, rotation frequency, and propagation mode on turbine performance through three-dimensional simulation. The results show that as the pressure amplitude of the BPW increases, the pressure oscillation at each section of the turbine increases and a local subcritical flow state will appear, leading to the decrease of turbine flowrate and turbine power, as well as an intensification of instantaneous turbine power fluctuations. As the rotation frequency of the BPW increases, the pressure oscillation at each section of the turbine gradually decreases. The flowrate and power of the turbine do not change much, but turbine efficiency gradually decreases. Compared to the aligned mode, the turbine performs better under the influence of BPW in misaligned mode. Compared to the single-wave mode, the fluctuation of transient turbine power is lower under the influence of BPW in the multiwave mode excluding collision mode. Finally, the constraints of equal flowrate region and equal turbine power line on the peak-to-peak value of the BPW were analyzed when the joint operation of the turbine and compressor was not affected. The rotation frequency and mode of BPW will affect the flowrate region and power line.

Mitigating vibration from building systems in a second-floor laboratory

A second-floor laboratory reported excessive vibrations that were impacting the calibration of microscopes, as well as human comfort. Based on a review of the building floor plans and discussions with the Design-Build team, potential vibration sources were narrowed to various MEP equipment in the first-floor mechanical room, rooftop, and outdoor utility pad. Vibration measurements were collected in the laboratory and near each piece of mechanical equipment as the equipment was turned ON and OFF to determine its vibration impact on the laboratory. The narrowband frequency data indicated that the rotational frequency of the ceiling-mounted hot water pumps coincided with the frequencies of excessive vibration in the lab. Vibration isolation for the hot water pumps and surrounding piping and equipment was reviewed, and recommendations were provided based on ASHRAE guidance to minimize vibration propagation to the laboratory.

Microwave-Assisted Pyrolysis of Carbon Fiber-Reinforced Polymers and Optimization Using the Box-Behnken Response Surface Methodology Tool.

This article introduces an eco-friendly method for the reclamation of carbon fiber-reinforced polymers (CFRP). The research project involved numerous experiments using microwave-assisted pyrolysis (MAP) to explore a range of factors, such as the inert gas flow, the power level, the On/Off frequency of rotation, and the reaction duration. To design the experiments, the three-level Box-Behnken optimization tool was employed. To determine the individual and combined effects of the input parameters on the thermal decomposition of the resin, the data were analyzed using least-squares variance adjustment. The results demonstrate that the models developed in this study were successful in predicting the direct parameters of influence in the microwave-assisted decomposition of CFRPs. An optimal set of operating conditions was found to be the maximum nitrogen flow (2.9 L/min) and the maximum operating experimental power (914 W). In addition, it was observed that the reactor vessel's On/Off rotation frequency and that increasing the reaction time beyond 6 min had no significant influence on the resin elimination percentage when compared to the two other parameters, i.e., power and carrier gas flow rate. Consequently, the above-mentioned conditions resulted in a maximum resin elimination percentage of 79.6%. Following successful MAP, various post-pyrolysis treatments were employed. These included mechanical abrasion using quartz sand, chemical dissolution, thermal oxidative treatment using a microwave (MW) applicator and thermal oxidative treatment in a conventional furnace. Among these post-treatment techniques, thermal oxidation and chemical dissolution were found to be the most efficient methods, eliminating 100% of the carbon black content on the surface of the recovered carbon fibers. Finally, SEM evaluations and XPS analysis were conducted to compare the surface morphology and elementary constitution of the recovered carbon fibers with virgin carbon fibers.

Timing irregularities and glitches from the pulsar monitoring campaign at IAR

Pulsars have a very stable rotation overall. However, sudden increases in their rotation frequency, known as glitches, perturb their evolution. While many observatories commonly detect large glitches, small glitches are harder to detect because of the lack of daily cadence observations over long periods of time (years). We aim to explore and characterise the timing behaviour of young pulsars on daily timescales, looking for small glitches and other irregularities, in order to further our comprehension of the real distribution of glitch sizes. Our findings have consequences for the theoretical modelling of the glitch mechanism. We observed six pulsars with up to daily cadence between December 2019 and January 2024 with the two antennas of the Argentine Institute of Radio Astronomy (IAR). We used standard pulsar timing tools to obtain the times of arrival of the pulses and to characterise the pulsar's rotation. We developed an algorithm to look for small timing events in the data and calculate the changes in the frequency (nu ) and its derivative ($ at those epochs. We find that the rotation of all pulsars in this dataset is affected by small step changes in nu and $ Among them, we find three new glitches that have not been reported before: two glitches in PSR J1048$-$5832 with relative sizes of $ $ and $ $, and one glitch in the Vela pulsar with a size of $ $. We also report new decay terms on the 2021 Vela giant glitch, and on the 2022 giant glitches in PSR J0742$-$2822 and PSR J1740$-$3015, respectively. In addition, we find that the red noise contribution significantly diminished in PSR J0742$-$2822 after its giant glitch in 2022. Our results highlight the importance of high-cadence monitoring with an exhaustive analysis of the residuals to better characterise the distribution of glitch sizes and to deepen our understanding of the mechanisms behind glitches, red noise, and timing irregularities.

The impact of radiative levitation on mode excitation of main-sequence B-type pulsators

Context. Numerical computations of stellar oscillations for models representative of B-type stars predict fewer modes to be excited than observations reveal from modern space-based photometric data. One shortcoming of state-of-the-art evolution models of B-type stars that may cause a lack of excited modes is the absence of microscopic diffusion in most such models. Aims. We investigate whether the inclusion of microscopic diffusion in stellar models of B-type stars, notably radiative levitation experienced by isotopes, leads to extra mode driving by the opacity mechanism compared to the case of models that do not include microscopic diffusion. Methods. We consider the case of slowly to moderately rotating stars and use non-rotating equilibrium models, while we account for (uniform) rotation in the computations of the pulsation frequencies. We calculate 1D stellar structure and evolution models with and without microscopic diffusion and examine the effect of radiative levitation on mode excitation, for both low-radial order pressure and gravity modes and for high-radial order gravity modes. As is common practice in asteroseismology, rotation is included in the pulsation computations according to the mode’s frequency regime. For modes having frequencies below twice the rotation frequency, that is, modes in the sub-inertial regime, we adopt the traditional approximation of rotation. For modes in the super-inertial regime with frequency above twice the rotation frequency, rotation is treated perturbatively up to first order in the rotation. We consider macroscopic envelope mixing induced by internal gravity waves to compute the modes and study its effect on the surface abundances. Results. We find systematically more modes to be excited for the stellar models including microscopic diffusion compared to those without it, in agreement with observational findings of pulsating B-type dwarfs. Furthermore, the models with microscopic diffusion predict that excited modes occur earlier on in the evolution compared to modes without it. In order to maintain realistic surface abundances during the main sequence, we include macroscopic envelope mixing by internal gravity waves. Along with microscopic diffusion, such macroscopic envelope mixing ensures both more excited modes and surface abundances consistent with spectroscopic studies of B-type stars. Conclusions. While radiative levitation has so far largely been neglected in stellar evolution computations of B-type stars for computational convenience, it impacts mode excitation predictions for stellar models of such stars. We conclude that the process of radiative levitation is able to reduce the discrepancy between predicted and observed excited pulsation modes in B-type stars.

Method for Two-Stage Radar Measurement of the Blade Repetition Rate of a Propeller-Driven Aircraft

Introduction. Radar images of aircraft propellers can significantly improve the quality of their recognition and protection against simulating interference. Such images can be obtained using algorithms based on an inverse antenna aperture synthesis. A key factor determining the quality of image acquisition is the accuracy of the rotor blade rotation frequency measurement. In 2019, a method for measuring the blade repetition rate was proposed, which is based on convolution of the "secondary" signal modulation spectrum while simultaneously eliminating the influence of the Doppler frequency of the signal reflected from the aircraft body. In sequential analysis, the number of cycles is determined by the ratio of the maximum blade repetition rate (hundreds of hertz) to the discrete frequency shift (thousandths of hertz). In this case, to solve the measurement problem, the required number of cycles should be hundreds of thousands, which is expensive in terms of practical implementation.Aim. Development of a two-stage method for measuring the blade repetition rate, which allows the number of signal convolution cycles to be reduced by hundreds of times.Materials and methods. The proposed method is aimed at implementing adaptation circuits to an a priori unknown rotor speed of an aircraft, which can be determined based on the blade rotation frequency. The method involves measuring the blade frequency in two stages: a rough measurement of the blade frequency rate followed by its accurate measurement within the limits of the maximum errors of the rough measurement.Results. A method for a two-stage measurement of the blade repetition rate as applied to the construction of radar images of aircraft propellers is proposed. The feasibility of the method is illustrated by the example of a signal reflected from a Mi-8 helicopter. The requirements to the measurement error of the blade repetition rate and to the frequency analysis step at the precise measurement stage are formulated. The requirement to the repetition rate of probing signals is substantiated, the fulfillment of which ensures an unambiguous restoration of the spectrum of "secondary" modulation of the signal reflected from the blades of a propeller-driven aircraft.Conclusion. The developed method for a two-stage measurement of the blade repetition rate ensures the adaptation of algorithms for constructing radar images of aircraft propellers to their rotation frequency.