Vol 17, No 2 (2018)

Synthesis of the height control system for an unmanned aerial vehicle (UAV) with a soft wing, like a paraglider or a powered parachute, is considered in the article. An UAV is described, its scheme is shown, the forces and moments acting on it in the longitudinal plane are examined. A mathematical model of UAV motion is described in a body-axis coordinate system. Direct control is provided by the thrust motor. The thrust motor is mounted on the UAV so that the thrust is directed along the OX axis in the OXY plane. It is proposed to form the height control law on the basis of the thrust moment, which gives the advantage of stabilizing the angular velocity and the pitch angle. To synthesize the control and stabilization systems, the backstepping method is applied. According to this method, the task of developing a control law for the entire system is divided into a sequence of respective subtasks to lower-order subsystems. The algorithm of backstepping consists in making each integrator of the object stable by adding the feedback computed from this algorithm. The resulting control takes into account the nonlinearity of the object and depends on the entire state vector. The main advantages of the regulator obtained are: the system is stable within a broad range of input values; by varying the regulator coefficients, you can easily select the desired characteristics of control quality. The results of numerical simulation of UAV motion with the regulator obtained in the MATLAB environment are presented in the article.

A method of low-cycle fatigue equivalent tests based on the application of test specimens whose stress-strain state shall be similar to the stress-strain state of the part to be investigated is proposed in the paper. The stiffness ratio of the stressed state is used as the similarity criterion of stress and strain state of the specimens and the part. The method was successfully applied on the low-pressure compressor disk of a gas turbine engine. Specimens with a circular cross section and a V-concentrator were used as equivalent specimens. The tests were carried out as follows: the specimens were tested under stretching and compression for the zero-to-compression stress cycle; the disks were tested on a dedicated test bench with the spin-up of up to 5000 rpm. The proposed method of equivalent tests makes it possible to forecast low-cycle fatigue life of large-sized critical parts whose full-scale tests cannot be carried out. The method can also be used to assess the high-cycle fatigue life of parts and to forecast their long-term strength. The obtained equations make it possible to design and optimize the construction of aviation parts: the permissible value of strain rate in the most strained area of the part can be determined by the specified fatigue life.

The article describes surface hardening of aircraft engine titanium-alloy hydraulic cylinder face using the method of electro-spark doping by low-energy discharges. Graphite electrodes were used to provide functional behavior of the cylinder surface layer. The carbon oxide layer formed has a highly dispersed structure of a complex composition (with particles of titanium carbide, titanium oxide, graphite), 3-10 micron thick, characterized by high hardness and sliding properties. Graphite electrode alloying practically does not change the part dimensions. Subsequent diamond burnishing of the hardened surfaces decreases the value of the friction coefficient and surface roughness. Healing of defects and micro-cracks improves the fatigue resistance of the part. The developed technology makes it possible to assure the characteristics required of hydraulic cylinder work surfaces and increase their life.

The biological module BINOM is a platform for multi-purpose biomedical space experiments with a wide range of biological objects (bacteria, algae, fungi, plants, multicomponent ecosystems). It was designed as a payload for SamSat nanosatellites and can be easily mounted on any other space vehicle. The module consists of three main blocks – a sealed chamber for biological objects, a life support system, a system of control and measurement supporting scientific data acquisition and pre-processing. The BiNOM interacts with the electronic systems of the nanosatellite with the help of a single four-pin connector. The life support system maintains the required temperature, pressure, humidity and gas mixture composition in the chamber of the biological object. The control system makes it possible to carry out biomedical experiments in the automatic mode according to a specified program or by commands from the ground control post. The control system is designed to measure the parameters of the environment and the biological object. The module supports visualization of objects in the UV-VIS-IR spectral range, fluorescence analysis, temperature and humidity measurement at several points, pressure, concentration of oxygen and carbon dioxide. Additional sensors can be used depending on the goals of the experiment. A module prototype was made and a number of tests were carried out to confirm the adequacy of the engineering solutions proposed. In particular, the vacuum chamber tests showed that the pressure loss in the pressure hull does not exceed 20% per year. A number of biological experiments demonstrated the possibility of initialization, growth and life support of various biological objects during a long, up to two months, period.

The article describes a methodology of experimental determination of dynamic behavior of rocket and space equipment, using the example of AIST-2D small spacecraft. Experimentally obtained modal characteristics (natural modes and frequencies) are compared with modal characteristics calculated for the said spacecraft using a finite element model (FEM). The natural modes and frequencies of the spacecraft were experimentally obtained using scanning laser vibrometry; the modal analysis was performed using finite elements and the MSC. Patran / Nastran FEM package. The objectives and tasks are formulated; the main stages of modal analysis are described. It is necessary to update the finite-element models of spacecraft parts to obtain precise loads applied to such parts. During the tests target resonance frequencies of the test object were obtained for the 5-130 Hz range, as this range contains the first modes of the structure. Since the spacecraft is characterized by many uncertainties in stiffness parameters, the error of determining own frequencies was as high as 45.75% at the first stage of the research, which confirms the necessity of carrying out modal analysis. Dynamic characteristics of spacecraft structural elements obtained during the research will allow creating more precise and reliable spacecraft dynamic models at the design stage; this, in its turn, will improve precision of load calculations and reliability of the spacecraft in general.

Modifying the working surface of a product by applying protective and functional coatings makes possible considerable changes in the mechanical, optical, electrical, magnetic, thermal and chemical properties of the original structural material, its real surface, producing articles with protective, for example, anti-corrosion, wear-resistant and other properties. We investigated the possibility of improving the friction units of aircraft power plants by applying nanostructured ceramic composite spray coatings. A heavily loaded bearing forming a part of the gearbox of a turbojet engine is used as a prototype of the friction unit. The advantages and drawbacks of improved friction units as compared to production models and their prototypes made according to an improved technology are assessed. The results obtained during the experimental work are presented. A positive conclusion is made about the use of nanostructured composite materials in the development of friction units; the most favorable method of coating is determined.

Traditionally, sheet stamping is carried out in the cold state of the workpiece being processed. At the same time, due to the limited plasticity of the workpiece, stamping parts of complex shape is performed in several operating steps, which significantly increases the cost of production. The article is devoted to the development and research of a device providing stamping of parts with heating of the workpiece being processed. The device comprises a die and a working cylinder between which  the workpiece is placed, as well as a combustion chamber separated from the working cylinder by a piston. The heating of the sheet billet and its punching is carried out in two stages within 1...2 s with its exposure to the action of gas mixture combustion products. At the first stage, the billet is heated and deformed by the combustion products formed in the die cavity and the working cylinder, whereas at the second stage these processes take place due to the energy of the combustion products formed in the combustion chamber. The workflow of the developed device was studied. The regularities of the pressure and temperature changes of the gas that heats and deforms the billet being stamped were established. The optimum proportions of the volumes of the combustion chamber and the working cylinder were determined. The developed device ensures stamping of complex-shaped parts in one process step due to the heating of the workpiece. In this device the pressure on the surface of the workpiece being processed is 2...3 times higher compared with the existing analogues, which ensures stamping of heavy-thickness parts, as well as parts made of hard-to-deform alloys.

The article reviews domestic and foreign methods of estimating heat generation in angular contact ball bearings. Models for general-purpose bearings and for aviation angular contact ball bearings are considered. Models adopted at bearing manufacturers FAG (Germany) and SKF (Sweden) are considered for general-purpose bearings. Models developed at the KAI, CIAM named after P.I. Baranov and MTU (Germany) are considered for aviation bearings. The results of heat generation obtained in testing bearings 126206 (30×62×16 mm) and 176126 (130×200×33 mm) are presented. The calculated heat generation values, obtained by various methods, are compared with the experimental data. On the basis of the research the models that yield the calculated values of heat generation in ball bearings closest to the experimental data are specified. They can be used to estimate heat generation in aviation roller bearings with oil jet lubrication.

Porous materials, including bulk materials, are widely used for cleaning liquid and gaseous media from mechanical impurities, as heat insulating materials, working bodies in various technologies of mechanical engineering, power engineering, metallurgy, chemistry, petroleum chemistry, food industry, pharmacology, etc. The aim of the work is mathematical modeling of heat transfer in disperse bulk media, their melting, engineering assessment of a number of indicators essential in practice. A bulk disperse medium consisting of solid particles (lumps) of different shapes, sizes and composition, randomly arranged relative to each other, is considered. The article provides relationships for determining effective density, heat capacity, thermal conductivity, taking into account radiant heat transfer between particles (lumps) as applied to porous bulk materials. Using the obtained relationships, the model problem of heating and subsequent melting of the disperse medium under consideration is solved. The melting rate and the relaxation time during which the system consisting of melt and lumps comes to thermodynamic equilibrium are assessed. Though only one-dimensional thermal processes are considered in this paper, the proposed approach can be extended to two- and three-dimensional cases and applied for mathematical description of thermal behavior of nonmetallic porous materials. It is these materials that are mainly used for thermal insulation. Their behavior, especially in extreme, abnormal conditions is of great interest.

Creating web-applications is illustrated by an example of developing a multiuser web-interface for the computer-aided search of solving systems of non-linear equations in the Django package. The automated system is implemented in the Python programming language. Creation of a web application is proposed based on the client-server technology, where the client part implements the user interface, forms requests to the server and processes the responses from it. The server part receives the request from the client, performs the necessary calculations, then forms a web page and sends it to the client online. The developed application is designed for solving systems of nonlinear equations. The system has the ability to solve systems of equations of any dimensionality, save the solutions on the server and the PC, and to visualize the step-by-step process of solving and plotting. The system efficiency was tested on real data. For example, gas turbine engine parameters were calculated and the obtained results were used to design a 3D model of a gas turbine engine