Vol 17, No 3 (2018)

The paper presents results of complex research of vibration behavior of the differential reduction gear unit of a turboprop engine on the basis of statistics of products with repaired reduction gears and those placed under repair. The conducted research made it possible to establish the source of resonant oscillations of the compressor design elements leading to their breakage. It is established that this source is determined by the kinematics of the reduction gear unit and is associated with the wear of its gear teeth.  Standards for the intensity of the appropriate discrete component of the reduction gear vibration spectrum and those for the amount of permissible wear are substantiated and established on the basis of the work carried out. A complex of diagnostic parameters of wear based on intensity components of the auto-spectrum and the spectrum of maxima, the depth of amplitude modulation in some narrow-band processes, their characteristics based on the parameters of the current frequency and mutual characteristics was identified. It is shown that for the whole complex of the diagnostic parameters obtained their dependence on the wear value is satisfactorily approximated by a linear characteristic. The obtained results can serve as a basis for the development of a complex of methods of differential reduction gear vibration diagnostics.

The article deals with the use of telemetric information, namely data on emergencies, failures and malfunctions occurring on AIST small satellites. These data are used for the refinement of standard algorithms of satellite operable state recovery. To this end, an analysis was made of the accumulated volume of telemetric information, consisting of two stages: searching for parameters exceeding the acceptable limits and establishing the causes of emergencies. A detailed study of the causes and consequences of emergencies made it possible to create two fault trees reflecting the ways of the propagation of failures in the small satellite onboard equipment. The use of fault trees and information on emergencies made it possible to refine the algorithms for the operable state recovery developed at the stage of designing AIST small satellites. Two examples of refined algorithms allowing the recovery of the operable state of small satellites after failure of on-board equipment are given in the article.

Gas pressure pulsations are one of the main parameters taken into account in gas turbine engine development. Therefore, special attention is paid to the accuracy of measuring pressure fluctuations. A high temperature of gas flow, sensor’s size limitations in many cases do not allow it to be installed directly at the measurement point. There is a need to connect the sensor to the process using a waveguide channel (waveguide). It is known that resonant oscillations occur in the waveguide, leading to an additional dynamic error of the measuring channel. To improve the accuracy of measuring pressure fluctuations, corrective elements are used. A device consisting of a pressure pulsation sensor, a waveguide connected to the process, and a correction element is called a pressure pulsation probe in technical literature. In foreign and domestic literature there is a large amount of information on probes, but because of the variety of schemes of probe correction selecting those that would provide the required accuracy of measurement of pressure pulsations always poses a challenge. Therefore, taking into account the constant increase in the energy intensity of modern engines, and, accordingly, the increase in the temperature of working media, the authors analyzed the effectiveness of corrective elements on the basis of available patents, articles, and monographs. The article considers hardware and software schemes of correction of dynamic characteristics of acoustic probes based on corrective elements with distributed and lumped parameters. The advantages and disadvantages of the schemes are pointed out. Information on methods of calculating frequency characteristics of probes and their digital correction in the processing of experimental data is presented. The article will be of interest to developers of pressure pulsation probes and engineering and technical workers involved in GTE refinement.

The article presents an analysis of promising directions of improving the design and layout schemes of power plants of modern long-range interception aircraft, related to the implementation of the capabilities of bypass turbojet engines. Research of power plants of unconventional design-layout schemes opens significant prospects for improving flight performance of the long-range intercept aviation systems. These are primarily engines with variable parameters of the work process due to wider control of the elements in the flow passage. In engines with variable parameters the elements of the flow duct – compressor guide vanes, turbine nozzle guide vanes, the exhaust system, the combustion chamber and other elements are controlled. Additional components are used that can be switched off or over during the operation of the power plant (combustion chambers in the bypass duct, bypass valves, turbofan adapters), which ensures the adaptation of the engine operation mode to the flight conditions due to the integrated control system adapted to possible failures and malfunctions. It is expedient to use the range of the interception line in the case of a typical flight profile and providing the specified values of the maximum flight speed and altitude as a criterion of efficiency. It is shown that the computational methods based on mathematical modeling are an effective tool for justifying the decision-making in choosing rational values of the parameters of the work process of aviation gas turbine engines.

The article presents the results of comparison of computation data on the energy parameters of the working process of engines and the thermal condition of the structure obtained for low-thrust rocket engines fueled by gaseous oxygen-hydrogen, using various schemes of mixture formation. The analysis of the efficiency of the working process is carried out on the basis of the patterns of distribution of combustion products temperature in the cross sections of combustion chambers, temperature diagrams, their values in the area of the engine chamber wall and the specific thrust impulse. It is shown that the chosen tools fully characterize the efficiency of the working process implemented in various schemes of mixing in engines and make it possible to assess the quality of a particular scheme. It was found that for most of the parameters used and additional criteria for evaluating the efficiency of the mixture formation scheme for low-thrust rocket engines, the scheme implementing a rotational coaxial multistage flow of gaseous fuel components in the chamber is preferable.

The article provides an analytical overview of previously created engines, those in operational service and engines being developed for unmanned military-purpose aerial vehicles. The current state of the engine fleet, modern problems of development and production of domestic engines are described. It is shown that modern unmanned military-purpose aerial vehicles use a variety of types of power plants, for which their main technical characteristics, design and layout schemes are given. Some projects carried out under the program of import substitution are disclosed. The results of work conducted at the Department of Aircraft Engines of the Air Force Academy named after Professor N.E. Zhukovsky and Y.A. Gagarin are presented. The article outlines critical technologies for creating full-size gas turbine engines for the most complex and expensive class of heavy unmanned combat air vehicles with a take-off weight of more than 10 tons, designed to solve a wide range of tasks, including strategic ones. On the basis of the analysis of the existing unmanned systems conclusions were drawn as to the choice of the type of engine depending on their take-off weight. The basic directions of further development of power plants for one of the most dynamically developing branches of aviation – unmanned air vehicles - were forecast.

The decision on creation of a new energy-efficient vibration screen using combination parametrical resonance is presented. The decision makes it possible to expand functional and operational opportunities of vibration machines. Dynamic and mathematical models of a dual-mass resonant vibration screen are presented. Differential equations of the machine motion are given. The principle of work of a resonant vibration screen is described. The trajectory of motion of the center of mass of the system of pendulums of the inertia member of the parametrical drive during their running in on racetracks is given. A method of reducing the data on a dual-mass system to a single-mass one is presented. At the same time an additional condition on the stiffness of elastic members of the oscillatory system is introduced. The value of the coercive force under steady-state resonant oscillations is identified. Ratios between the masses of actuating devices, damping coefficients and linear displacements of the actuating device are obtained. The parametric resonance coupled with the phenomenon of self-synchronization makes it possible to realize self-controlled and self-supported proper motion of the machine. Real samples of dual-mass oscillatory systems with one and two parametrical vibration generators are presented. On the basis of the results obtained for prototypes of a dual-mass system the conclusion about the stability of the resonant operating mode is drawn. The results of this work can be used to produce new highly efficient resonant vibration machines.

The article discusses questions of shaping honeycomb panels for turbojet engine noise insulation casings. Various types of structures and materials used for manufacturing honeycomb panels are presented. Samples were tested to determine mechanical characteristics. The technology of manufacturing honeycomb panels was determined by the value of relative elongation. The main rejection criteria in forming panels on bending and stretching presses were reviewed. The process of shaping honeycomb panels using computer numerical control (CNC) equipment was analyzed. Force parameters of the shaping process required for the assessment of the stress-strain state and obtaining the control program were determined. The values of the spring action were calculated for single-layer and double-layer panels using the A.A. Ilyushin unloading theorem. It was found that the springing of single-layer and two-layer panels differs due to the magnitude of the generalized rigidity. The value of springing is determined by the known height of the honeycomb panel. Designs of honeycomb panels with different positions of the middle layer along the height of the panel are given. Graphs showing the dependence of the punch radius adjusted for the value of springing on the radius of the part for various types of structures from titanium alloys and stainless steels are presented.