Medium-sized Unmanned Aerial Vehicles Research Articles

Effects of a Self-Pressurized Injection Strategy on the Formation of a Stratified Mixture and the Combustion of an Aviation Kerosene Piston Engine

Abstract The aviation kerosene piston engine (AKPE) is the main power system for small- and medium-sized unmanned aerial vehicles (UAVs). Conventional AKPEs use carburetors or port fuel injection (PFI) as fuel supply, resulting in poor cold start performance and difficulty in forming an economically efficient stratified mixture. In addition, two-stroke AKPEs using carburetors or PFI have serious scavenging losses. These reasons lead to the poor economic performance of conventional AKPEs. Direct injection (DI) can be controlled through precise injection timing to form a stratified mixture. The combustion of stratified mixtures in engines can effectively improve the fuel economy and endurance flight time characteristics of UAVs. As a special DI injector, self-pressurized injectors have great potential in the power field of UAVs. To effectively apply self-pressurized injectors on UAV engines and improve the economy, an engine model and a self-pressurized injector spray model are established and verified in this paper. The single injection strategy and segmented injection strategy for forming stratified mixtures are explored, and the combustion performance is studied. The main conclusions are as follows: the optimal installation angle of the injector is 15 deg, which yields excellent results in the formation of the mixture at this angle. When the fuel injection quantity is small, utilizing a single injection strategy combined with delaying the end of the injection phase (EOIP) can form a stratified mixture. Reducing the angle difference between the EOIP and the ignition timing can improve the power and economy. As the fuel injection quantity is large, a stratified mixture can be formed through two-stage injection. When the fuel injection ratio is 4:1, the uniformity of the mixture distribution in the combustion chamber is significantly improved. Adjusting the second EOIP between a 35 deg crank angle (CA) before top dead center (BTDC) and a 30 deg CA BTDC can achieve a stratified mixture with good economy and power performance.

Research and calculate flight navigation parameters using data from the angular speed sensor and long acceleration sensor

Today, along with the development of science and technology, inertial navigation systems are applied with precision sensors and high-speed specialized digital computers. With the advantages of compactness and ease of integration and installation on aircraft, this type of navigation system is effectively applied to small and medium-sized unmanned aerial vehicles. When combined with other systems of the same function, such as satellite navigation systems, radio altimeter systems, barometric altimeter systems, etc., this system allows for the provision of angle and position information with high precision. In this paper, the Inertial Labs INS-P Professional Single Antenna GPS-Aided Inertial Navigation System was selected by the authors to improve the aircraft navigation system.

ICI-Robust Transceiver Design for Integration of MIMO-OFDM Radar and MU-MIMO Communication

By virtue of the low cost and flexible deployment, unmanned aerial vehicles (UAVs) are becoming the most promising platform for active radar sensing to find targets in shaded areas and build a temporary communication infrastructure at disaster sites. Radar and wireless communication are essential functions for reliable control of UAVs and real-time exchange of sensed measurements. However, due to the limited payload and power budget of UAVs, it is impossible to mount two individual radar and communication systems, especially on small- or medium-sized UAVs. Recently, joint communication and radar (JCR) systems have emerged as a breakthrough, which perform the communication and radar functions simultaneously on the same hardware platform. Compared to a simple combination of individual communication and radar systems, a UAV JCR system can minimize the implementation cost, power consumption, payload, and radio resource usage. This paper proposes transmit beamformer and receive beamformer designs for a UAV network composed of a UAV JCR base station, a target, and multiple user equipments. Specifically, the UAV transmits an orthogonal frequency division multiplexing (OFDM)-modulated waveform with transmit and receive beamforming to perform multi-input multi-output (MIMO) radar and multiuser-MIMO (MU-MIMO) communication functions simultaneously. Unlike the previous OFDM radar scheme that employs the communication symbol repetition method, a novel receive beamformer design is proposed to resolve the inter-carrier interference problem in the range/velocity estimation process, which therefore does not sacrifice the communication transmission rate. As a result, simulation results show that the proposed scheme achieves a higher radar signal-to-clutter ratio while achieving a higher communication sum-rate than existing schemes.

Embedded Payload Solutions in UAVs for Medium and Small Package Delivery

Investigations about the feasibility of delivery systems with unmanned aerial vehicles (UAVs) or drones have been recently expanded, owing to the exponential demand for goods to be delivered in the recent years, which has been further increased by the COVID-19 pandemic. UAV delivery can provide new contactless delivery strategies, in addition to applications for medical items, such as blood, medicines, or vaccines. The safe delivery of goods is paramount for such applications, which is facilitated if the payload is embedded in the main drone body. In this paper, we investigate payload solutions for medium and small package delivery (up to 5 kg) with a medium-sized UAV (maximum takeoff of less than 25 kg), focusing on (i) embedded solutions (packaging hosted in the drone fuselage), (ii) compatibility with transportation of medical items, and (iii) user-oriented design (usability and safety). We evaluate the design process for possible payload solutions, from an analysis of the package design (material selection, shape definition, and product industrialization) to package integration with the drone fuselage (possible solutions and comparison of quick-release systems). We present a prototype for an industrialized package, a right prism with an octagonal section made of high-performance double-wall cardboard, and introduce a set of concepts for a quick-release system, which are compared with a set of six functional parameters (mass, realization, accessibility, locking, protection, and resistance). Further analyses are already ongoing, with the aim of integrating monitoring and control capabilities into the package design to assess the condition of the delivered goods during transportation.

Acoustic detection of unmanned aerial vehicles using biologically inspired vision processing.

Robust detection of acoustically quiet, slow-moving, small unmanned aerial vehicles is challenging. A biologically inspired vision approach applied to the acoustic detection of unmanned aerial vehicles is proposed and demonstrated. The early vision system of insects significantly enhances signal-to-noise ratios in complex, cluttered, and low-light (noisy) scenes. Traditional time-frequency analysis allows acoustic signals to be visualized as images using spectrograms and correlograms. The signals of interest in these representations of acoustic signals, such as linearly related harmonics or broadband correlation peaks, essentially offer equivalence to meaningful image patterns immersed in noise. By applying a model of the photoreceptor stage of the hoverfly vision system, it is shown that the acoustic patterns can be enhanced and noise greatly suppressed. Compared with traditional narrowband and broadband techniques, the bio-inspired processing can extend the maximum detectable distance of the small and medium-sized unmanned aerial vehicles by between 30% and 50%, while simultaneously increasing the accuracy of flight parameter and trajectory estimations.

Architecture of Distributed Control System for Gearbox-Free More Electric Turbofan Engine

This article presents the development of the electric turbofan engine in distributed architecture with a design thrust in the range of 3 to 7.5 and from 7.5 to 30 kN for small and medium-sized unmanned aerial vehicles. The engine subsystems are considered as separate smart modules with a built-in control system, exchanging data via a digital channel with the central engine control and diagnostics unit. The key smart engine units are combined in the following subsystems: starter and turbine generators, oil pumps, actuator of guide vanes, fuel pumps, fuel metering unit, control and diagnostic unit. All pumps and guide vane actuator are electrically driven. Control and monitoring signals are transmitted via a digital bus. Functional and reliability analysis and the technical configuration design of each subsystem are presented. Based on analysis of the architecture of distributed control systems for a gearbox-free electric engine, different configurations of described subsystems are proposed.

Computational Fluid Dynamic Analysis of Flow Rate Performance of a Small Piezoelectric-Hydraulic Pump

This paper investigates the transient flow rate performance of small piezoelectric-hydraulic pumps. In a previous study, a small piezoelectric hydraulic pump was designed and developed to be applicable to the braking systems of small- and medium-sized UAVs (unmanned aerial vehicles). To this end, a thin plate spring check valve was designed in order to effectively discharge the flow in a single direction. The flow rate of the piezoelectric-hydraulic pump is an important criterion for evaluating pump efficiency. Therefore, a study on the parameters affecting such a flow rate is necessary to enhance the efficiency of piezoelectric hydraulic pumps used in brake systems. This study on small piezoelectric-hydraulic pumps is performed to accurately predict the flow rate using a CFD (Computational Fluid Dynamics) tool. In other words, an unsteady CFD method is applied to model the transient flow rate characteristics and the internal flow field of the fluid. The visualization of the internal flow field is evaluated for a better understanding of the flow fields inside the pump. Moreover, this work also illustrates the detailed motion of both the inlet and outlet check valves during the pump operation that fully reflects the phase shift between the check valves and the piston motion, all of which affect the flow rate performance of the pump. An experiment of flow rate characteristics was conducted on a designed piezoelectric-hydraulic pump, which verifies the validity of the CFD results.

Radar Surveillance of Unmanned Aerial Vehicles (Review)

Radar surveillance of unmanned aerial vehicles (UAVs) is actively developing area of scientific research. This article provides a review and analysis of publications in recent years devoted to the methods and radar systems of detection and recognition of classes and types of UAVs. It is noted that the most difficult targets for radar detection are low-sized, low-speed small UAVs (drones) flying at low and extremely low altitudes. If large and medium-sized UAVs can be detected by modern radar systems, then for the detection of small UAVs it is advisable to create specialized highly efficient, highly mobile, portable and inexpensive active UAV detection radars. The technical requirements for such radars are defined and recommendations for their implementation are provided. High-performance protection systems based on adaptive lattice filters are offered to protect UAV detection radars from noise jamming and passive interference. It is shown that the research on the methods of recognizing UAV classes and types is a development of the existing theory and technology of radar recognition of air targets.

Investigation on the Performance Characteristics of 2-Stroke Heavy Fuel Light Aeroengine (2SHFLA) with Different Fuel Injection Systems: Modeling and Comparative Simulation

Extensive application of small and medium-sized unmanned aerial vehicles (UAVs) have already made the development of corresponding power system a research hotspot nowadays. Two-stroke heavy fuel light aeroengine (2SHFLA) is selected as the research focus in this paper. The working principle of 2SHFLA with different fuel injection systems is elaborated systematically. By dividing the initial prototype engine into several subsystems, the simulation platform is set up with its key model parameters accurately calibrated against the test data. Simulation platforms of the other two types of engines are subsequently constructed based on the pre-calibrated simulation platform of the initial prototype engine. Afterwards, comparative simulation is performed and the corresponding simulation results include: (1) comparison of performance characteristics of the initial prototype engine fueled with regular gasoline/heavy fuel; (2) comprehensive comparison of the performance characteristics of all the three types of engine.

Effect of O-ring Deformation on Saturated Load Pressure of the Small Piezoelectric-Hydraulic Pump Brake System

This paper examines the effect of deformation of the O-ring on maximum pressure in the load side of the small piezoelectric-hydraulic pump brake system. In the previous study, the small piezoelectric-hydraulic pump braking system used for small- and medium-sized unmanned aerial vehicles was developed. To operate the brake system, load pressure must be formed. The magnitude of the load pressure is determined by the pressure in the chamber and the adapted check valve type. Therefore, a study of the parameters affecting the chamber pressure is necessary to improve the load side pressure. The volume change of the O-ring seal has a complicated effect on the maximum pressure in the chamber of the piezoelectric-hydraulic pump. Accordingly, this study analyzed the effect of the O-ring on chamber pressure, considering the changing volume of the O-ring seal with nonlinear property material. The deformation of the O-ring made of nitrile-butadiene rubber was investigated using the finite-element method. In addition, the optimal radius of the piston was determined to obtain the maximum chamber pressure. The obtained maximum pressure and optimal radius are verified by comparison with the pressurization experiment using the developed small piezoelectric-hydraulic pump brake system.

Smart Relay Architecture for Over-the-Horizon High Quality Communications With Unmanned Aerial Vehicles

This paper presents a system architecture to accomplish over-the-horizon communications with medium-sized unmanned aerial vehicles (UAV) in order to enhance its autonomy and maximum range. This architecture is based on using a second UAV as a communication relay with a compact active circular array with separated transmitting and receiving elements at C-band. The designed active feeding network provides switching capabilities in order to selectively activate these elements depending on the desired direction of the antenna beam, achieving maximum equivalent isotropic radiated power (EIRP) in transmission and maximum antenna gain in reception. In this way, a bidirectional long-range link for telemetry, telecommand, and high-resolution video can be deployed between UAVs providing high quality of service, reliability, and moderate data throughput at an affordable cost. Based on the measurements of a manufactured prototype, the maximum range of the deployed air-air link using the designed system is estimated in 20 km, considerably increasing the performance of current systems based on the use of omnidirectional antennas onboard UAVs.

A novel endurance prediction method of series connected lithium-ion batteries based on the voltage change rate and iterative calculation

High-power lithium-ion battery packs are widely used in large and medium-sized unmanned aerial vehicles and other fields, but there is a safety hazard problem with the application that needs to be solved. The generation mechanism and prevention measurement research is carried out on the battery management system for the unmanned aerial vehicles and the lithium-ion battery state monitoring. According to the group equivalent modeling demand of the battery packs, a new idea of compound equivalent circuit modeling is proposed and the model constructed to realize the accurate description of the working characteristics. In order to realize the high-precision state prediction, the improved unscented Kalman feedback correction mechanism is introduced, in which the simplified particle transforming is introduced and the voltage change rate is calculated to construct a new endurance prediction model. Considering the influence of the consistency difference between battery cells, a novel equilibrium state evaluation idea is applied, the calculation results of which are embedded in the equivalent modeling and iterative calculation to improve the prediction accuracy. The model parameters are identified by the Hybrid Pulse Power Characteristic test, in which the conclusion is that the mean value of the ohm internal resistance is 20.68 mΩ. The average internal resistance is 1.36 mΩ, and the mean capacitance value is 47747.9F. The state of charge prediction error is less than 2%, which provides a feasible way for the equivalent modeling, battery management system design and practical application of pack working lithium-ion batteries.

Scavenging Ports’ Optimal Design of a Two-Stroke Small Aeroengine Based on the Benson/Bradham Model

The two-stroke engine is a common power source for small and medium-sized unmanned aerial vehicles (UAV), which has wide civil and military applications. To improve the engine performance, we chose a prototype two-stroke small areoengine, and optimized the geometric parameters of the scavenging ports by performing one-dimensional (1D) and three-dimensional (3D) computational fluid dynamics (CFD) coupling simulations. The prototype engine is tested on a dynamometer to measure in-cylinder pressure curves, as a reference for subsequent simulations. A GT Power simulation model is established and validated against experimental data to provide initial conditions and boundary conditions for the subsequent AVL FIRE simulations. Four parameters are considered as optimal design factors in this research: Tilt angle of the central scavenging port, tilt angle of lateral scavenging ports, slip angle of lateral scavenging ports, and width ratio of the central scavenging port. An evaluation objective function based on the Benson/Bradham model is selected as the optimization goal. Two different operating conditions, including the take-off and cruise of the UAV are considered. The results include: (1) Orthogonal experiments are analyzed, and the significance of parameters are discussed; (2) the best factors combination is concluded, followed by simulation verification; (3) results before and after optimization are compared in details, including specific scavenging indexes (delivery ratio, trapping efficiency, scavenging efficiency, etc.), conventional performance indicators, and the sectional views of gas composition distribution inside the cylinder.

A modeling and simulation framework for UAVs utilizing 4G-LTE cellular networks

Only a small amount of work has been published on the topic of exploiting existing Long-Term Evolution-Advanced (LTE) cellular communication network infrastructure for Unmanned Aerial Vehicles (UAV) data links. This paper documents a modeling and simulation (m&s) framework that has been developed utilizing the powerful OMNeT[Formula: see text] simulation tool for assessing the feasibility and effectiveness of this prospect in various UAV scenarios. Using multiple scenarios, we have studied the data rate requirements for communications between small and medium-sized UAVs and base stations. Using this framework, we have shown that the data rate requirements for the links are within the data throughput achieved by LTE networks. The developed framework implements a propagation model endorsed by the 3GPP LTE project team and also accurately models the high mobility of UAVs. The framework is highly configurable and extensible and boasts of automatic aggregation of results and chart plotting. The outcomes of this research may be utilized by industry for rapidly deploying highly mobile, low-cost UAVs in a wide range of applications and scenarios.

Low Altitude UAV Air-to-Ground Channel Measurement and Modeling in Semiurban Environments

Small- and medium-sized unmanned aerial vehicles (UAVs) can fly for a short distance (<2 km) from a control station in a nonsegregated air space (altitudes < 100 m). It is of great interest to model the propagation channel under such condition, where there is an important influence from the environment. This paper presents multiple measurements carried out in low altitudes with a medium-sized UAV flying over a semiurban environment. Path loss exponent is given based on the measurements done at different altitudes and a height-dependent Rician K factor model is proposed. The results clearly reveal the existence of two propagation zones with very distinct channel characteristics. The breakpoint indicates the height where the condition of the channel changes rapidly. At low altitudes, the obstacles generate a large amount of multipath and the propagation is greatly affected, while at higher altitudes the influence mitigates. Our results are useful for the modeling of low altitude air-to-ground (AG) propagation channels and the performance analysis of UAV-enabling AG communication systems, such as the channel capacity and the throughput.

Mm-Wave SAR demonstrator as a test bed for advanced solutions in microwave imaging

The capability of imaging and surveying ground areas with airborne and spaceborne sensors has a very high priority in many applications, both in the civilian and military sectors. One of the most essential uses of this capability is in disaster monitoring, where up-to-date, reliable images and data are vital for the undertaking and coordinating of rescue actions. Sensors in space are very accurate but typically have a long revisit time, and thus their use for continuous monitoring is limited. Manned aircrafts equipped with optical, infrared, and synthetic aperture radar (SAR) are costly, and their operation in poor weather conditions (like heavy storms) are limited due to concerns over pilot safety. Unmanned aerial vehicles (UAV) are ideal candidates for the safe and cheap surveillance and imaging of such areas. They can provide continuous monitoring at very low cost, be deployed very quickly, and pose no risk of the loss of life in the case of a platform malfunction caused by heavy weather conditions, technical problems, or human error. The disadvantage of small, unmanned platforms is that they only offer limited space for payloads and have a low electrical power supply. This lays down the conditions for the design of an airborne sensor for small- and medium-sized UAVs. The cheapest solution for UAV surveillance is the use of visual light cameras. Optical cameras are cheap, light, and require a low supply of power, but their usage is limited to the daytime and good weather conditions. The presence of heavy rain, clouds, fog, or smoke can significantly reduce their imaging distance, sometimes down to just a few meters. Far better results can be obtained using much longer electromagnetic waves. The use of far infrared (e.g. in the 10 μm region) can provide thermal information and can be used for the detection of people in both day and night conditions, but it does not provide satisfactory images of land and infrastructures. The use of millimeter and centimeter microwaves with active illumination, combined with SAR technology, can provide high resolution images in all weather conditions, day and night, at a distance of several kilometers.

Digital Autoland Control Laws Using Quantitative Feedback Theory and Direct Digital Design

of several aircraft problems, but not for outer-loop control or for automatic landing. This paper describes the synthesis and development of an automatic landing controller for medium-sized unmanned aerial vehicles, using discrete quantitative feedback theory. Controllers for the localizer, glideslope tracker, and automatic flare are developed, with a focus on outer-loop synthesis and robustness with respect to model uncertainty. Linear, nonreal-time, six-degree-of-freedom Monte Carlo simulation is used to compare the quantitative feedback theory controller with a baseline proportional–integral controller in several still-air and turbulent-air landing scenarios. Results presented in the paper show that the quantitative feedback theory controller provides superior performance robustness to the proportional–integral controller in turbulent-air conditions when model uncertainties are present. It is therefore concluded to be a promising candidate for an autoland controller for unmanned air vehicles.