A steady trend of expanding the small aircraft fleet equipped with piston engines is observed today. Special fuel (aviation gasoline with specified operational properties) for aircraft piston engines (PE) ensuring their stable operation in all modes and under all operating conditions is used. The indicators of aviation fuels operational properties including gasoline are achieved by means of adding special additives. One of these additives is an anti-knock additive – tetraethyl lead (TEL) that is added into the fuel in a certain amount in an ethyl liquid form. Despite the excellent TEL properties as an anti-knock additive, it also has a number of significant disadvantages. From the point of view of aircraft engine operation, it is noted that the TEL combustion products (decomposition) that are not effectively removed from the combustion chamber, enter the oil system in a significant amount, causing fine oil filters clogging. The article notes that even a small content of TEL decomposition products in aviation oils deteriorates dramatically their pumping capacity and leads to complete fine oil filters clogging for few minutes of engine operation, even on fresh oil. Moreover, the multi-stage oil cleaning stipulated by the design of some PE does not have a significant impact on this negative factor posing a threat to flight safety. These days the lead-containing gasoline use for aviation PE has no alternative, so solutions to reduce the negative consequences while applying are required.

Today, technologies for the production of alternative fuels and for the development of engines on different operating principles are actively developing, due to both the tightening of the environmental requirements of ICAO (International Civil Aviation Organization) for harmful emissions into the atmosphere and the depletion of non-renewable resources, and the interests of the oil importing countries. Strict requirements are imposed on the quality of aviation fuels related to ensuring the reliability of aviation technology and flight safety. Requirement toughening for quality indicators will inevitably lead to higher fuel prices, so today we can observe some concessions in domestic and foreign regulatory documents to certain quality indicators of aviation fuels, for example, to indicators of low-temperature properties. It follows that the use of petroleum fuels will sooner or later become inappropriate. Technologies to produce synthetic and biological fuels from various types of raw materials make it possible to obtain fuel with close quality indicators to traditional kerosene, but it has not yet been completely replaced. Therefore, today we are considering the use of alternative fuels in a mixture with petroleum kerosene in various proportions. The question remains open: in what proportion is it possible to use mixtures of alternative fuel with kerosene on the aircraft without any negative consequences for their operation. Based on the known dependencies, a mathematical model is proposed for calculating some operational indicators of fuel, engine and aircraft depending on the proportion of mixing alternative fuel and kerosene. In accordance with the calculations, the most rational ratio of petroleum kerosene and SPK fuel is substantiated both from the point of view of the necessary operational properties and from the point of view of economic feasibility.

Aircraft airworthiness maintenance is carried out by a number of measures guaranteeing safe operation. TsAGI, SibNIIA, GosNIIGA and other organizations with a highly-efficient laboratory base conduct tests and studies of structures and structural elements to determine or extend the operational life in stages. The tests require the capability to recreate complex loading spectra and they can be lengthy and expensive. One of the main problems encountered during testing is its forcing. Forcing reduces the test time while maintaining the equivalence of the fatigue damage and structural failure accumulation mechanisms under real and model loading. For every stage, the operational life limit and durability, guaranteeing flight safety, are determined on the basis of laboratory tests, operation tests and prediction of expected operating conditions. At every stage, information about the emerging defects is accumulated, additional tests are carried out and technical measures, determining the aircraft structure or structural elements operational life and durability, are developed, and design, manufacture, maintenance and repair deficiencies are identified. One of the key issues is the fracture mechanics, which the assessment of the aircraft structures survivability is based on. The fatigue failure mechanism depends on many factors: operational load or its model; stress condition that occurs during testing; the material, which the structural elements are made of. Fatigue failure begins with the microcracks in the structural element weakened area. Under the loads action, often being a random process, the cracks propagation is quite intense and it leads to the destruction of the structure. To determine the durability of the samples, modeling the MS-21 fuselage longitudinal and cross joints, theoretical calculations and experimental studies were carried out, and it allowed to judge about the compliance of the results obtained by the loaded hole.

The control system sensors failures can cause the aircraft stability and controllability deterioration. Such failures fast and reliable inflight detection and localization allows minimization their consequences and prevention of an accident. Direct application of traditional parametric methods for sensors health monitoring with the use of their mathematical models is impossible due to the lack of information about the real inputs on their sensitive elements. This leads to the need for the problem of aircraft flight dynamics modeling with a high level of uncertainties to be solved, which complicates the application of functional test methods and determines the necessity of excessive sensors hardware redundancy. Widely known nonparametric methods either require a prior knowledge base, preliminary training, or long-term tuning on a large real flight data volume, or have low selective sensitivity for the failed sensors reliable localization. This paper expands the application of the well-known nonparametric failure detection criterion, based on the analysis of the linear dependence of the input-output data Hankel matrix columns and solution of the sensor failures localizing problem. Necessary and sufficient solvability conditions are given, the structure and the criterion values are determined in an analytical form before and after the failures occurrence. The proposed method does not require functional or hardware redundancy, prior information about the parameters of mathematical models and their stability, identification, observation, or prediction problems solution. The efficiency of the method is shown on the Boeing 747–100/200 longitudinal model example. Fast tuning, fast response and selective sensitivity of the developed algorithms are noted.

When designing a stabilization system for highly maneuverable unmanned aerial vehicles (UAVs), one of the relevant tasks is to study the operation of the steering drive in the frequency band corresponding to the flexural vibrations of the UAV body. To ensure the stability of the UAV stabilization system, quite conflicting requirements may be imposed on the dynamic characteristics of the drive. In particular, the requirement for a sharp suppression of the amplitude-frequency characteristic at the frequency of UAV bending vibrations with minimal phase distortions in the control band of the longitudinal and lateral channels of the stabilization system can significantly complicate the task of researching the stability of the UAV motion control system. The article discusses an electric drive prototype with a digital microcontroller, designed for a highly maneuverable UAV. Adaptive algorithms of the digital controller make it possible to provide the necessary phase delays in the control frequency band and at the same time almost completely suppress the harmonic components of the control signals at the frequencies of the bending vibrations of the UAV body. The algorithms are essentially nonlinear in nature and are based on a change in the gain of the direct circuit of the drive depending on the frequency of the input signal, which greatly complicates the calculation of the transfer function of the steering drive for use in the frequency model of the stabilization system. Generally, the steering drive is described by a linear minimum-phase system, presented as a transfer function of one of the typical blocks of the first or second order, but for the specified steering drive with given dynamic characteristics, this approach is untenable. As a result of the study, a method for obtaining a frequency model of the steering drive is proposed, which is implemented as a non-minimum phase system, the main property of which is the independence of the amplitude-frequency and phase-frequency characteristics. In the process of research, the results obtained on the proposed model are compared with the results of experiments on a drive prototype and its complete non-linear time model. The main advantage of the proposed frequency model is a fairly simple description of the steering drive in the frequency domain, convenient for use as part of the frequency model of the stabilization system in the study of problems of ensuring the stability of UAV flight.

A modern large-sized aircraft dynamic properties analysis, determined by the specificity of its layout scheme, demonstrates that the engines on under the wing elastic pylons lightly damped oscillations cause a number of undesirable phenomena, including intense accumulation of fatigue damage of the pylon-to-the-wing attachment, in fact in the area of engine installation in the pylon and the wing. The results of theoretical and experimental research show that with some engine attachment to the pylon structural modification it becomes possible to use the engines inertial and gyroscopic properties to absorb these oscillations. In this case, the motor tones damping coefficients increase by an order of magnitude or even more, so the gyroscopic coupling of elastic vibration tones is realized. With the rational choice of the additional parameters of elastic and dissipative bonds in the engine attachments it is possible to affect the aircraft wing and engines aero elastic vibrations effectively, which has a significant effect on the aircraft elements structural capabilities. A mathematical model of aero elasticity (MMAE) with respect to the kinetic moment of the engine rotors and specially designed units for attaching the engines to the pylons was developed in order to study the influence and the selection of rational elastic-dissipative parameters of the pylons-under-the-wing aircraft engine mounts. The method of predetermined basic forms is used for the aircraft with running engines on the pylons MMAE synthesis. The given forms are considered as the aircraft basic structure forms natural vibrations in the void. This work treats the engine nacelle and the rotor as absolutely rigid bodies, the elasticity of the rotor to the nacelle attachment is neglected. The pylon is modeled by an elastic beam, and the elastic and dissipative properties of the pylon-to-the-wing and the engine-to-the-pylon attachments are correspondingly by elastic-dissipative bonds. Schematic diagrams of the engine to the pylon attachments are proposed. The results of the study devoted to the influence of the proposed attachment points modifications on the load and integral strength characteristics of the main structural elements of the engine – pylon – wing dynamic system on the example of an An-124 aircraft are presented. The practical implementation of the proposed solutions aimed to reduce the level of fatigue damage to structural elements of the aircraft feasibility is proved.

It has been shown that with air transportation rise it is necessary to increase the efficiency of storm and wastewater purification from the territory of the airports and other air enterprises. It is suggested to use higher aquatic vegetation to protect the environment from airborne pollutants into natural water reservoirs. For further step of final cleanup it is proposed to use aquatic hyacinth – Eichornia. The rationalization for the plant selection is provided, its essential characteristics and the way for extracting pollutants out of the aquatic environment during the metabolism process are described. The technique of experiments on determining the effectiveness of biological wastewater purification within the conditions of the central part of the country is discussed in terms of Moscow region. The measurement results of suspended materials and petrochemicals concentrations in water before and after purification in sediment ponds are presented. The effectiveness of biological purification is shown. The possibility of using water hyacinth for purification of some superficial water reservoirs is also outlined. It is recommended all the year round to use protecting constructions (covers) in open purification plants, then under protected conditions metabolism processes can proceed in the rhizome, stems and foliage of the vegetation even in the autumn-winter period. It is proposed to recycle the used biomass for commercial purposes as a livestock fodder additive under the certain conditions that have been defined. The algorithm of preserving seedlings in the cold season and their subsequent planting in water reservoirs in spring is discussed. It is economically feasible to use biological final purification by aquatic hyacinth but observing the unusual environmental safety measures that have been formulated is required. Practicability of further prospective work on producing specialized ecosystems involving higher aquatic vegetation for nature-like integrated purification of certain types of wastewater was underlined.