Semi-empiric noise modeling of a Cargo eVTOL UAV by means of system identification from flight noise measurement data

This publication shows the semi-empiric noise modeling of an electric-powered vertical takeoff and landing (eVTOL) unmanned aerial vehicle (UAV) by means of system identification from flight noise measurement data. This work aims to provide noise models with a compact analytical ansatz for horizontal and vertical flight which are suited for integration into a geographical information system. Therefore, flight noise measurement campaigns were conducted and evaluated. An existing noise model ansatz is adapted to the eVTOL UAV under consideration and noise models are computed from the measurement data using the output error method. The resulting models are checked for plausibility by comparing them to technical literature. The horizontal flight noise model is subjected to a correlation analysis and the influence of meteorological effects are examined. To achieve a higher level of accuracy in future noise modelings, an optimization of the microphone positions as well as the flight trajectory is carried out.

Impact of Chinese and European Airspace Constraints on Trajectory Optimization

Air traffic trajectory optimization is a complex, multidimensional and non-linear optimization problem and requires a firm focus on the essential criteria. The criteria cover operational, economical, environmental, political, and social factors and differ from continent to continent. Since air traffic is a transcontinental transport system, the criteria may also change during a single flight. Historic flight track data allow observation and assess real flights, to extract essential criteria and to derive optimization strategies to increase air traffic efficiency. Real flight track data from the Chinese and European air traffic show significant differences in the routing structure in both regions. For that reason, reference trajectories of historic ADS-B 24-h air traffic data in China and Europe have been extracted and analyzed regarding horizontal flight efficiency and the most restrictive criteria of trajectory optimization. We found that prohibited areas might be the most powerful reason to describe deviations from the great circle distance in the Chinese air traffic system. Atmospheric conditions, network requirements, aircraft types and flight planning procedures are similar in China and Europe and only have a minor impact on flight efficiency during the cruise phase. In a multi-criteria trajectory optimization of the extracted reference trajectories considering the weather, operational constraints and prohibited areas, we found that flown ground distances could be reduced by 255 km in the Chinese airspace and 2.3 km in the European airspace. The resultant reference trajectories can be used for further analysis to increase the efficiency of continental air traffic flows.

A Two-Point Approximation Approach to Determining Aircraft Aerodynamic Force Coefficients for a Maximal-Duration Horizontal Flight

This paper proposes a two-point approximation approach to determining aircraft aerodynamic force coefficients, and compares it to the traditional methods. A variational concept is used to conduct aircraft flight trials for the maximal duration of quasi-horizontal flights. The advantages of the described optimization theories are demonstrated, in terms of aviation fuel gas savings. The results of a numerical example are presented.

Analytical Synthesis of Control Acceleration of Unmanned Aerial Vehicle

. The problem of analytical synthesis of the control acceleration for an unmanned aerial vehicle (UAV) during its flight along a complex trajectory, consisting of sequentially located horizontal flight sections, located at different heights relative to the earth's surface has been solved in the paper. The problem has been solved as an analytical definition of the optimal control of a linear non-stationary system for a specified minimized quality functional. The mathematical model of the system is presented in the form of differential equations of UAV motion in the vertical plane of a fixed coordinate system related to the earth's surface. A feature of the proposed methodology for solving the problem is the substantiation of the original form of the minimized functional and parameters included in the law of variation of the control acceleration obtained by known methods. As the components of the quality functional, the values of coordinates and velocity of the UAV are considered and they are specified at the corresponding points in space through which the UAV path must pass, in order to obtain the optimal curvature of the trajectory. The derived mathematical dependences make it possible to implement them on board of an aircraft and, ultimately, solve the problem of ensuring the minimum energy consumption when controlling an object (UAV). Computer simulation of the analytically obtained results in the form of the UAV flight trajectory and the processes of changing its acceleration and speed have shown the efficiency of the proposed technique and the prospects of its use at the initial stage of the synthesis of the UAV control system.

Розрахункове дослідження аеродинамічних характеристик рульового гвинта вертольота типу Мі-8 з урахуванням інтерференції з несучим гвинтом на режимі висіння при боковому вітрі

Under certain conditions of a helicopter flight, the main rotor can exert a rather strong effect on the tail rotor, changing its traction and power characteristics. The calculated and experimental characteristics of an isolated tail rotor under such operating conditions can differ significantly from those under conditions of interaction with the main rotor. The study of this phenomenon is an urgent task, since a change in the characteristics of the tail rotor and the conditions of its operation in the presence of the main rotor can cause a decrease in controllability margins and, as a consequence, the cause of an aircraft accident, for example, the so-called. "left rotation" of the helicopter. Since 1985, on helicopters from M. L. Mile, 42 aviation accidents occurred in units and subdivisions of the state and civil aviation of the USSR (and now Russia) due to helicopters falling into spontaneous left rotation. Over the past 10 years, 29 accidents (8 accidents and 21 accidents) have occurred for this reason. 29 helicopters were lost: 20 Mi-8, 5 Mi-24, 4 Mi-2. Experience shows that getting into an uncontrolled left rotation in almost 100% of cases ends with a collision of the helicopter with the ground and overturning it on the starboard side. The interaction of the main and tail rotor is most significantly manifested in the modes of horizontal flight with sliding at low speeds and hovering in crosswind conditions. This is due to the peculiarities of the formation of the main rotor vortex wake. In this article, the case of aerodynamic interference of the main rotor and several helicopter configurations in horizontal flight mode with the low speed with sliding (hovering in a crosswind) is considered. Using the methods of computational fluid dynamics, the degree of influence of the main rotor on the tail rotor was investigated in the described modes. The most severe operating modes of the tail rotor of each configuration have been determined. Based on the results of calculations, the most rational configuration of the tail rotor has been chosen, which has the greatest reserves of controllability under unfavorable operating conditions. The results obtained have been used in the design of a new perspective helicopter, modernization of the existing fleet, as well as improving the flight safety level.

Determination of the flight trajectory in terms of emission and fuel consumption minimization

The present-day world is characterized by the intense development of air transport. However, along with it, significant problems appear. Among these problems, the most important are those relating to safety and negative impact of air transport on the environment. Air transport efficiency and profitability issues, although not critical, must also be taken into account because they decide about the intensity of development of this branch of transport. There are currently two large programs in Europe oriented at improving safety, environmental, and efficiency indicators. These are SESAR 2020 and Clean Sky 2, being a continuation of previous ones. One of the ways to reduce negative impact of air transport on the environment and improve its efficiency is to reduce fuel consumption and pollutants emissions resulting from fuel combustion. To find solutions with the abovementioned features, it is necessary to have sufficiently accurate models to estimate the amount of fuel consumed and the amount of pollutants emitted. Developing a sufficiently accurate model to determine fuel consumption and pollutants emission was performed. Due to the specificity of the missions carried out by passenger aircraft, the focus was on the cruise stage when aircraft flies at a constant altitude with a constant air speed. The result of the analysis was the development of methodology for fuel consumption and emission of main pollutants in cruise conditions. Specific fuel consumption is calculated for the thrust required for horizontal flight at cruising altitude. Emission indexes for CO, NOx, HC, and CO2 for the cruise have been determined based on known indexes for the landing and take-off cycle phase, after applying appropriate corrections. An illustration of the application of the developed methodology was the optimization of a medium-sized transport aircraft trajectory on a selected connection to determine a trajectory characterized by a minimum emission value taking into account weather conditions.

The lifting force of an airplane wing when flying horizontally at high speeds. Explanation of the vortex trail.

In this paper, an explanation is given of the lift force of an airplane during horizontal flight. It is shown that during a flight, five vertical forces act on the airplane: gravity; pressure gradient with a minus sign; Archimedes force; potential force and the vortex force obtained from the action minimum. The first three forces were known before. The potential force was also known from the Bernoulli equation, but its effect on the airfoil from the air had not previously been taken into account. The vortex force obtained from the minimum action in the application to a continuous medium was not taken into account in aerodynamics. In horizontal flight the vortex force is directed upwards, it compensates for the gravity of the airplane at high speed commensurate with the speed of sound. The paper provides an explanation of the vortex trail behind the airplane, mentioned in the Millennium problem Navier-Stokes equation.

Energy Conversion System and Control of Fuel-Cell and Battery-Based Hybrid Drive for Light Aircraft

The paper presents a power electronic conversion system and its control for a fuel cell and a battery-based hybrid drive system for a motor glider. The energy conversion system is designed in such a way that the fuel cell gives power equal to the electric drive power demand for horizontal flight, whereas during motor glider take-off and climbing, the fuel cell is supported by the battery. The paper presents the power demand related to the assumed mission profile, the main components of the hybrid drive system and its holistic structure, and details of power electronics control. Selected stationary experimental test results related to the energy conversion and drive system are shown. Some results related to the aircraft tests on a runway are presented.

Application of pressure head theory to determine the aerodynamic characteristics of the helicopter main rotor

A method is proposed for calculating main aerodynamic characteristics of the main rotor of the Mi-26 helicopter: a lift, a reactive moment, a required power of the propulsion system, a speed of the inductive air flow, a throttle response coefficient, a speed of the horizontal flight. This method based on the pressure propeller theory. The parameters of the Mi-26 helicopter and the propeller of the experimental setup calculated according to the pressure theory of the main rotor are experimentally confirmed. The percentage of the discrepancy between the statistical data on the aerodynamic characteristics of the Mi-26 helicopter rotor calculated with the pressure theory does not exceed 1.5%.

MODELLING THE HELICOPTER ROTOR AERODYNAMICS AT FORWARD FLIGHT WITH FREE WAKE MODEL AND URANS METHOD

The presented work is dedicated to the numerical study of the aerodynamic characteristics of the helicopter rotor. Two approaches to modeling of the rotor are applied: the free wake model developed by the Authors with using steady airfoil characteristics and the Unsteady RANS method based on the Ansys Fluent software. The modes of hovering and horizontal flight in the range of advancing ratio μ = (0-0.45) are considered. The shapes of the rotor wake, the distributions of the normal force coefficient and the fields of inductive velocities for all considered flight modes are calculated. For a particular case with μ = 0.25 there is a comparison with experimental data. The time needed for calculation of the applied methods is estimated. Accuracy of the used methods in the framework of the solved task is analysed with taking into account used models assumptions. It is shown that in the range of μ = (0-0.25) the free wake model provides a fast and reliable calculation of the aerodynamic characteristics of the helicopter rotor. For values of μ > 0.35 it is necessary to take into account the unsteady characteristics of the airfoil.