Topical Collection "Unmanned Aerial Systems"

A topical collection in Aerospace (ISSN 2226-4310). This collection belongs to the section "Aeronautics".

Editors

Dr. David Anderson
E-Mail Website
Collection Editor
Aerospace Sciences Research Division, School of Engineering, University of Glasgow, Glasgow, Scotland, UK
Interests: autonomous systems; multi-agent & multi-resolution simulation; nonlinear control; operational analysis and flight dynamics & control
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Javaan Chahl
E-Mail Website
Collection Editor
Sensor Systems, School of Engineering, University of South Australia, Adelaide 5001, Australia
Interests: aerospace automation; unmanned aerial vehicles; defence systems; biologically inspired vision systems; biologically inspired flight systems; space exploration technology; vision; robots; UAV; surveillance; sensors; biomimetics
Dr. Michael Wing
E-Mail Website
Collection Editor
Director of Aerial Information Systems Laboratory, Forest Engineering, Resources and Management Department, Oregon State University, 204 Peavy Hall, Corvallis, OR 97331, USA
Interests: Unmanned Aerial Systems (UAS); Geographic Information Systems (GIS); Land Cover Change; Global Positioning Systems (GPS); Remote Sensing; Land Surveying and Geodesy; Visualization and Visibility Analysis; Crime Mapping and Analysis; Geographic Information Science; Digital Measurement Tools for Natural Resource Applications; Stream Habitat; Precision Forestry; Spatial Statistics

Topical Collection Information

Dear Colleagues,

Once perceived as a niche application, Unmanned Aerial Systems (UAS) are now well established as a serious sector within the aerospace industry. The global marketplace for UAS technology has seen the sharpest growth of any aerospace sector for the past decade and this trend is predicted to continue well into the 21st century. Currently, the most prolific UAS application is military surveillance, where UAS systems have proven to be invaluable in recent conflicts. However, such uses merely scratch the surface of potential UAS applications—the real challenge facing researchers is to develop technologies to enable widespread adoption of UAS in civilian airspace, both controlled and urban.

Research in UAS requires expertise from disciplines across the academic and industrial spectra. Advances in computing and communications bandwidth for example have allowed aerodynamicists and aircraft structural engineers to explore the design space in a manner impossible even a few years ago. This is especially true in the domain of small-UAS, where a number of new platform designs from tail-sitters and stop-rotors to compound configurations have recently been proposed. Not new ideas, granted, but configurations now realisable within an unmanned aircraft setting. Unmanned systems have therefore created an opportunity for novelty, innovation and creativity in aerospace design not seen for half a century. Another key research area is in unmanned aircraft operations analysis. Here, new application areas for UAS are discovered as advances in airborne sensing, autonomy and precise platform control flow into UAS designs, yielding greater performance and capability.

The challenges in realising the true potential of UAS are not all technical. Societal factors must be addressed, particularly the negative stereotype of the ‘drone’. Such challenges may be overcome in part by developing innovative new design and analysis methods for improving and demonstrating UAS safety and reliability. We invite papers either addressing the research opportunities outlined here or in the general topic area of unmanned aerial vehicles that will make a substantive contribution to the state of the art.

Dr. David Anderson
Prof. Dr. Javaan Chahl
Dr. Michael Wing
Collection Editors

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Keywords

  • autonomous systems
  • aerospace sensor technologies
  • aerodynamic technologies
  • systems engineering
  • guidance navigation and control
  • unmanned systems operational analysis/air traffic management
  • system of systems simulation
  • aerospace design and optimization
  • aerospace propulsion
  • smart materials and structures
  • composite structures and health monitoring
  • rotorcraft
  • flight safety
  • reconfigurable/fault tolerant control
  • flight dynamics
  • small unmanned aerial vehicles

Related Special Issue

Published Papers (49 papers)

2022

Jump to: 2021, 2020, 2019, 2018, 2017, 2016, 2015

Article
Trajectory Tracking Based on Active Disturbance Rejection Control for Compound Unmanned Aircraft
Aerospace 2022, 9(6), 313; https://doi.org/10.3390/aerospace9060313 - 09 Jun 2022
Viewed by 550
Abstract
The compound unmanned aircraft is provided with three primary flight modes, which are helicopter flight mode in low forward speed flight, airplane flight mode in high forward speed flight and transition flight mode in middle forward speed flight. For the different flight modes, [...] Read more.
The compound unmanned aircraft is provided with three primary flight modes, which are helicopter flight mode in low forward speed flight, airplane flight mode in high forward speed flight and transition flight mode in middle forward speed flight. For the different flight modes, an appropriate flight control law is the need to ensure good flying qualities. In this paper, a trajectory tracking control system based on the active disturbance rejection controller (ADRC) for the compound unmanned aircraft is proposed to adapt the full flight modes. A flight dynamics model and a Simulink simulation model of the compound unmanned aircraft are developed. The transition flight control strategy is analyzed and synthesized to meet the requirement of control strategy in the full flight modes. The internal uncertainties and external disturbance of the UAV are estimated with an extended state observer to compensate control input. A genetic algorithm-particle swarm optimization (GA-PSO) algorithm is utilized to optimize the controller parameters. The simulation of route tracking and spiral climb with different flight modes is conducted, which demonstrates the tracking ability, interference rejection, robustness and effectiveness of the developed controller in the full flight modes. Full article
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Article
A Cyber-Physical Prototyping and Testing Framework to Enable the Rapid Development of UAVs
Aerospace 2022, 9(5), 270; https://doi.org/10.3390/aerospace9050270 - 17 May 2022
Viewed by 604
Abstract
In this work, a cyber-physical prototyping and testing framework to enable the rapid development of UAVs is conceived and demonstrated. The UAV Development Framework is an extension of the typical iterative engineering design and development process, specifically applied to the rapid development of [...] Read more.
In this work, a cyber-physical prototyping and testing framework to enable the rapid development of UAVs is conceived and demonstrated. The UAV Development Framework is an extension of the typical iterative engineering design and development process, specifically applied to the rapid development of UAVs. Unlike other development frameworks in the literature, the presented framework allows for iteration throughout the entire development process from design to construction, using a mixture of simulated and real-life testing as well as cross-aircraft development. The framework presented includes low- and high-order methods and tools that can be applied to a broad range of fixed-wing UAVs and can either be combined and executed simultaneously or be executed sequentially. As part of this work, seven novel and enhanced methods and tools were developed that apply to fixed-wing UAVs in the areas of: flight testing, measurement, modeling and emulation, and optimization. A demonstration of the framework to quickly develop an unmanned aircraft for agricultural field surveillance is presented. Full article
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Article
Architectural Process for Flight Control Software of Unmanned Aerial Vehicle with Module-Level Portability
Aerospace 2022, 9(2), 62; https://doi.org/10.3390/aerospace9020062 - 25 Jan 2022
Viewed by 834
Abstract
To apply UAVs (Unmanned Aerial Vehicle) into different fields, including research and industry, and expand it quickly, reliable but modular software is required. The existing flight control software (FCS) of the UAV consists of various types of modules categorized into different layers, and [...] Read more.
To apply UAVs (Unmanned Aerial Vehicle) into different fields, including research and industry, and expand it quickly, reliable but modular software is required. The existing flight control software (FCS) of the UAV consists of various types of modules categorized into different layers, and it is responsible for coordinating, monitoring, and controlling the vehicle during its flight. This paper proposes mpFCS, a structure of UAV flight control software, which provides portability to its modules and is easy to expand. The mpFCS consists of four segments and several modules within the segments. mpFCS provides portability for each module within the segment. Existing software does not provide portability for its modules because of the tight coupling resulting from its different and private interfaces. The mpFCS uses interfaces of the standard airborne software architecture to transfer data between its modules. Moreover, the structure provides portability for its modules to run in the standard airborne software environment. In order to verify the mpFCS, we tested the mpFCS with the conformance test suite of the airborne software that provides the testing environment for the interfaces and modules of the software. The mpFCS passed the test. Test results show that all modules of the mpFCS are portable. Additionally, portable modules can be interoperable with other software, and the structure is expandable with new modules that use standard airborne software interfaces. Full article
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Article
An End-to-End UAV Simulation Platform for Visual SLAM and Navigation
Aerospace 2022, 9(2), 48; https://doi.org/10.3390/aerospace9020048 - 19 Jan 2022
Cited by 1 | Viewed by 1038
Abstract
Visual simultaneous localization and mapping (v-SLAM) and navigation of unmanned aerial vehicles (UAVs) are receiving increasing attention in both research and education. However, extensive physical testing can be expensive and time-consuming due to safety precautions, battery constraints, and the complexity of hardware setups. [...] Read more.
Visual simultaneous localization and mapping (v-SLAM) and navigation of unmanned aerial vehicles (UAVs) are receiving increasing attention in both research and education. However, extensive physical testing can be expensive and time-consuming due to safety precautions, battery constraints, and the complexity of hardware setups. For the efficient development of navigation algorithms and autonomous systems, as well as for education purposes, the ROS-Gazebo-PX4 simulator was customized in-depth, integrated into our previous released research works, and provided as an end-to-end simulation (E2ES) solution for UAV, v-SLAM, and navigation applications. Unlike most other similar works, which can only stimulate certain parts of the navigation algorithms, the E2ES platform simulates all of the localization, mapping, and path-planning kits in one simulator. The navigation stack performs well in the E2ES test bench with the absolute pose errors of 0.3 m (translation) and 0.9 degree (rotation), respectively, for an 83 m length trajectory. Moreover, the E2ES provides an out-of-box, click-and-fly autonomy in UAV navigation. The project source code is opened for the benefit of the research community. Full article
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2021

Jump to: 2022, 2020, 2019, 2018, 2017, 2016, 2015

Article
A Simplified FE Modeling Strategy for the Drop Process Simulation Analysis of Light and Small Drone
Aerospace 2021, 8(12), 387; https://doi.org/10.3390/aerospace8120387 - 09 Dec 2021
Cited by 1 | Viewed by 844
Abstract
The numerical accuracy of drop process simulation and collision response for drones is primarily determined by the finite element modeling method and simplified method of drone airframe structure. For light and small drones exhibiting diverse shapes and configurations, mixed materials and structures, deformation [...] Read more.
The numerical accuracy of drop process simulation and collision response for drones is primarily determined by the finite element modeling method and simplified method of drone airframe structure. For light and small drones exhibiting diverse shapes and configurations, mixed materials and structures, deformation and complex destruction behaviors, the way of developing a reasonable and easily achieved high-precision simplified modeling method by ensuring the calculation accuracy and saving the calculation cost has aroused increasing concern in impact dynamics simulation. In the present study, the full-size modeling and simplified modeling methods that are specific to different components of a relatively popular light and small drone were analyzed in an LS-DYNA software environment. First, a full-size high-precision model of the drone was built, and the model accuracy was verified by performing the drop tests at the component level as well as the whole machine level. Subsequently, based on the full-size high-precision model, the property characteristics of the main components of the light and small drone and their common simplification methods were classified, a series of simplified modeling methods for different components were developed, several single simplified models and combined simplified models were built, and a method to assess the calculation error of the peak impact load in the simplified models was proposed. Lastly, by comparing and analyzing the calculation accuracy of various simplified models, the high-precision simplified modeling strategy was formulated, and the suggestions were proposed for the impact dynamics simulation of the light and small drone falling. Given the analysis of the calculation scale and solution time of the simplified model, the high-precision simplified modeling method developed here is capable of noticeably reducing the modeling difficulty, the solution scale and the calculation time while ensuring the calculation accuracy. Moreover, it shows promising applications in several fields (e.g., structure design, strength analysis and impact process simulation of drone). Full article
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Article
A Detailed Survey and Future Directions of Unmanned Aerial Vehicles (UAVs) with Potential Applications
Aerospace 2021, 8(12), 363; https://doi.org/10.3390/aerospace8120363 - 25 Nov 2021
Cited by 10 | Viewed by 1436
Abstract
Recently, unmanned aerial vehicles (UAVs), also known as drones, have gained widespread interest in civilian and military applications, which has led to the development of novel UAVs that can perform various operations. UAVs are aircraft that can fly without the need of a [...] Read more.
Recently, unmanned aerial vehicles (UAVs), also known as drones, have gained widespread interest in civilian and military applications, which has led to the development of novel UAVs that can perform various operations. UAVs are aircraft that can fly without the need of a human pilot onboard, meaning they can fly either autonomously or be remotely piloted. They can be equipped with multiple sensors, including cameras, inertial measurement units (IMUs), LiDAR, and GPS, to collect and transmit data in real time. Due to the demand for UAVs in various applications such as precision agriculture, search and rescue, wireless communications, and surveillance, several types of UAVs have been invented with different specifications for their size, weight, range and endurance, engine type, and configuration. Because of this variety, the design process and analysis are based on the type of UAV, with the availability of several control techniques that could be used to improve the flight of the UAV in order to avoid obstacles and potential collisions, as well as find the shortest path to save the battery life with the support of optimization techniques. However, UAVs face several challenges in order to fly smoothly, including collision avoidance, battery life, and intruders. This review paper presents UAVs’ classification, control applications, and future directions in industry and research interest. For the design process, fabrication, and analysis, various control approaches are discussed in detail. Furthermore, the challenges for UAVs, including battery charging, collision avoidance, and security, are also presented and discussed. Full article
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Article
Mutual Aerodynamic Interference Mechanism Analysis of an “X” Configuration Quadcopter
Aerospace 2021, 8(11), 349; https://doi.org/10.3390/aerospace8110349 - 16 Nov 2021
Viewed by 606
Abstract
This paper studies the quadcopter’s mutual interference phenomenon. The flow field of the quadcopter at different flight speeds is simulated by solving the three-dimensional unsteady Reynolds averaged Navier-Stokes equations with sliding mesh methods. “Virtual Modes” (VMs) are introduced to examine the mechanisms of [...] Read more.
This paper studies the quadcopter’s mutual interference phenomenon. The flow field of the quadcopter at different flight speeds is simulated by solving the three-dimensional unsteady Reynolds averaged Navier-Stokes equations with sliding mesh methods. “Virtual Modes” (VMs) are introduced to examine the mechanisms of aerodynamic interference among the quadcopter’s components (front rotors, rear rotors, and fuselage). By comparing the aerodynamic forces of different VMs, this work shows that mutual interference to the front rotors can be negligible, interference to the rear rotors is due to the wake of front rotors and fuselage, and mutual interference to fuselage is caused by front and rear rotors. Only the rear rotors’ thrust and pitch moment as well as the lift of the fuselage are significant. At the flight speed of 5–15 m/s, the mutual interference causes 11% loss of thrust and 35% loss of pitching moment to the rear rotors; In the cases of hovering and 25 m/s forward flight, the interference is negligible. Full article
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Article
Mission Oriented Multi-Prop UAV Analysis Using Statistical Design Trends
Aerospace 2021, 8(11), 321; https://doi.org/10.3390/aerospace8110321 - 28 Oct 2021
Cited by 1 | Viewed by 604
Abstract
This paper presents a methodology for the sizing and preliminary analysis of Multi-Prop UAVs. The methodology is founded on design trends that emerge from a vast and unique database that has been collected for such vehicles. The database includes geometry parameters, components’ weight, [...] Read more.
This paper presents a methodology for the sizing and preliminary analysis of Multi-Prop UAVs. The methodology is founded on design trends that emerge from a vast and unique database that has been collected for such vehicles. The database includes geometry parameters, components’ weight, the power required, and flight performance estimation. For a given mission, the analysis enables optimization of a specific design of a Multi-Prop configuration for either minimal weight or minimal dimensions. As opposed to low-order and relatively simple analyses that are typically used in early design stages, the results presented in this paper include design trends and correlations within existing flying configurations and, therefore, contain many design constraints that typically emerge only during advanced stages of the design process. Full article
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Article
Design of Low Altitude Long Endurance Solar-Powered UAV Using Genetic Algorithm
Aerospace 2021, 8(8), 228; https://doi.org/10.3390/aerospace8080228 - 16 Aug 2021
Cited by 3 | Viewed by 1388
Abstract
This paper presents a novel framework for the design of a low altitude long endurance solar-powered UAV for multiple-day flight. The genetic algorithm is used to optimize wing airfoil using CST parameterization, along with wing, horizontal and vertical tail geometry. The mass estimation [...] Read more.
This paper presents a novel framework for the design of a low altitude long endurance solar-powered UAV for multiple-day flight. The genetic algorithm is used to optimize wing airfoil using CST parameterization, along with wing, horizontal and vertical tail geometry. The mass estimation model presented in this paper is based on structural layout, design and available materials used in the fabrication of similar UAVs. This model also caters for additional weight due to the change in wing airfoil. The configuration is optimized for a user-defined static margin, thereby incorporating static stability in the optimization. Longitudinal and lateral control systems are developed for the optimized configuration using the inner–outer loop strategy with an LQR and PID controller, respectively. A six degree-of-freedom nonlinear simulation is performed for the validation of the proposed control scheme. The results of nonlinear simulations are in good agreement with static analysis, validating the complete design process. Full article
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Article
Propulsion Sizing Correlations for Electrical and Fuel Powered Unmanned Aerial Vehicles
Aerospace 2021, 8(7), 171; https://doi.org/10.3390/aerospace8070171 - 24 Jun 2021
Cited by 5 | Viewed by 1161
Abstract
Despite the increasing demand of Unmanned Aerial Vehicles (UAVs) for a wide range of civil applications, there are few methodologies for their initial sizing. Nowadays, classical methods, mainly developed for transport aircraft, have been adapted to UAVs. However, these tools are not always [...] Read more.
Despite the increasing demand of Unmanned Aerial Vehicles (UAVs) for a wide range of civil applications, there are few methodologies for their initial sizing. Nowadays, classical methods, mainly developed for transport aircraft, have been adapted to UAVs. However, these tools are not always suitable because they do not fully adapt to the plethora of geometrical and propulsive configurations that the UAV sector represents. Therefore, this work provides series of correlations based on off-the-shelf components for the preliminary sizing of propulsion systems for UAVs. This study encompassed electric and fuel-powered propulsion systems, considering that they are the most used in the UAV industry and are the basis of novel architectures such as hybrid propulsion. For these systems, weight correlations were derived, and, depending on data availability, correlations regarding their geometry and energy consumption are also provided. Furthermore, a flowchart for the implementation of the correlations in the UAV design procedure and two practical examples are provided to highlight their usability. To summarize, the main contribution of this work is to provide parametric tools to size rapidly the propulsion system components, which can be embedded in a UAV design and optimization framework. This research complements other correlation studies for UAVs, where the initial sizing of the vehicle is discussed. The present correlations suit multiple UAV categories ranging from micro to Medium-Altitude-Long-Endurance (MALE) UAVs. Full article
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Article
An Explosion Based Algorithm to Solve the Optimization Problem in Quadcopter Control
Aerospace 2021, 8(5), 125; https://doi.org/10.3390/aerospace8050125 - 27 Apr 2021
Viewed by 988
Abstract
This paper presents an optimization algorithm named Random Explosion Algorithm (REA). The fundamental idea of this algorithm is based on a simple concept of the explosion of an object. This object is commonly known as a particle: when exploded, it will randomly disperse [...] Read more.
This paper presents an optimization algorithm named Random Explosion Algorithm (REA). The fundamental idea of this algorithm is based on a simple concept of the explosion of an object. This object is commonly known as a particle: when exploded, it will randomly disperse fragments around the particle within the explosion radius. The fragment that will be considered as a search agent will fill the local space and search that particular region for the best fitness solution. The proposed algorithm was tested on 23 benchmark test functions, and the results are validated by a comparative study with eight well-known algorithms, which are Particle Swarm Optimization (PSO), Artificial Bee Colony (ABC), Genetic Algorithm (GA), Differential Evolution (DE), Multi-Verse Optimizer (MVO), Moth Flame Optimizer (MFO), Firefly Algorithm (FA), and Sooty Tern Optimization Algorithm (STOA). After that, the algorithm was implemented and analyzed for a quadrotor control application. Similarly, a comparative study with the other algorithms stated was done. The findings reveal that the REA can yield very competitive results. It also shows that the convergence analysis has proved that the REA can converge more quickly toward the global optimum than the other metaheuristic algorithms. For the control application result, the REA controller can better track the desired reference input with shorter rise time and settling time, lower percentage overshoot, and minimal steady-state error and root mean square error (RMSE). Full article
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Article
Online Identification-Verification-Prediction Method for Parallel System Control of UAVs
Aerospace 2021, 8(4), 99; https://doi.org/10.3390/aerospace8040099 - 02 Apr 2021
Cited by 1 | Viewed by 1035
Abstract
In order to solve the problem of how to efficiently control a large-scale swarm Unmanned Aerial Vehicle (UAV) system, which performs complex tasks with limited manpower in a non-ideal environment, this paper proposes a parallel UAV swarm control method. The key technology of [...] Read more.
In order to solve the problem of how to efficiently control a large-scale swarm Unmanned Aerial Vehicle (UAV) system, which performs complex tasks with limited manpower in a non-ideal environment, this paper proposes a parallel UAV swarm control method. The key technology of parallel control is to establish a one-to-one artificial UAV system corresponding to the aerial swarm UAV on the ground. This paper focuses on the computational experiments algorithm for artificial UAV system establishment, including data processing, model identification, model verification and state prediction. Furthermore, this paper performs a comprehensive flight mission with four common modes (climbing, level flighting, turning and descending) for verification. The results of the identification experiment present a good consistency between the outputs of the refined dynamics model and the real flight data. The prediction experiment results show that the prediction method in this paper can basically guarantee that the prediction states error is kept within 10% about 16 s. Full article
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Article
Unmanned Aerial Vehicle Operating Mode Classification Using Deep Residual Learning Feature Extraction
Aerospace 2021, 8(3), 79; https://doi.org/10.3390/aerospace8030079 - 16 Mar 2021
Cited by 7 | Viewed by 1243
Abstract
Unmanned Aerial Vehicles (UAVs) undoubtedly pose many security challenges. We need only look to the December 2018 Gatwick Airport incident for an example of the disruption UAVs can cause. In total, 1000 flights were grounded for 36 h over the Christmas period which [...] Read more.
Unmanned Aerial Vehicles (UAVs) undoubtedly pose many security challenges. We need only look to the December 2018 Gatwick Airport incident for an example of the disruption UAVs can cause. In total, 1000 flights were grounded for 36 h over the Christmas period which was estimated to cost over 50 million pounds. In this paper, we introduce a novel approach which considers UAV detection as an imagery classification problem. We consider signal representations Power Spectral Density (PSD); Spectrogram, Histogram and raw IQ constellation as graphical images presented to a deep Convolution Neural Network (CNN) ResNet50 for feature extraction. Pre-trained on ImageNet, transfer learning is utilised to mitigate the requirement for a large signal dataset. We evaluate performance through machine learning classifier Logistic Regression. Three popular UAVs are classified in different modes; switched on; hovering; flying; flying with video; and no UAV present, creating a total of 10 classes. Our results, validated with 5-fold cross validation and an independent dataset, show PSD representation to produce over 91% accuracy for 10 classifications. Our paper treats UAV detection as an imagery classification problem by presenting signal representations as images to a ResNet50, utilising the benefits of transfer learning and outperforming previous work in the field. Full article
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Article
Human–Machine Interface Design for Monitoring Safety Risks Associated with Operating Small Unmanned Aircraft Systems in Urban Areas
Aerospace 2021, 8(3), 71; https://doi.org/10.3390/aerospace8030071 - 10 Mar 2021
Cited by 6 | Viewed by 1414
Abstract
The envisioned introduction of autonomous Small Unmanned Aircraft Systems (sUAS) into low-altitude urban airspace necessitates high levels of system safety. Despite increased system autonomy, humans will most likely remain an essential component in assuring safety. This paper derives, applies, and evaluates a display [...] Read more.
The envisioned introduction of autonomous Small Unmanned Aircraft Systems (sUAS) into low-altitude urban airspace necessitates high levels of system safety. Despite increased system autonomy, humans will most likely remain an essential component in assuring safety. This paper derives, applies, and evaluates a display design concept that aims to support safety risk monitoring of multiple sUAS by a human operator. The concept comprises of five design principles. The core idea of the concept is to limit display complexity despite increasing the number of sUAS monitored by primarily visualizing highly abstracted information while hiding detailed information of lower abstraction, unless specifically requested by the human operator. States of highly abstracted functions are visualized by function-specific icons that change hue in accordance to specified system states. Simultaneously, the design concept aims to support the human operator in identifying off-nominal situations by implementing design properties that guide visual attention. The display was evaluated in a study with seven subject matter experts. Although preliminary, the results clearly favor the proposed display design concept. The advantages of the proposed design concept are demonstrated, and the next steps for further exploring the proposed display design concept are outlined. Full article
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2020

Jump to: 2022, 2021, 2019, 2018, 2017, 2016, 2015

Article
Method to Characterize Potential UAS Encounters Using Open Source Data
Aerospace 2020, 7(11), 158; https://doi.org/10.3390/aerospace7110158 - 04 Nov 2020
Cited by 1 | Viewed by 1208
Abstract
As unmanned aerial systems (UASs) increasingly integrate into the US national airspace system, there is an increasing need to characterize how commercial and recreational UASs may encounter each other. To inform the development and evaluation of safety critical technologies, we demonstrate a methodology [...] Read more.
As unmanned aerial systems (UASs) increasingly integrate into the US national airspace system, there is an increasing need to characterize how commercial and recreational UASs may encounter each other. To inform the development and evaluation of safety critical technologies, we demonstrate a methodology to analytically calculate all potential relative geometries between different UAS operations performing inspection missions. This method is based on a previously demonstrated technique that leverages open source geospatial information to generate representative unmanned aircraft trajectories. Using open source data and parallel processing techniques, we performed trillions of calculations to estimate the relative horizontal distance between geospatial points across sixteen locations. Full article
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Article
Risk Assessment for UAS Logistic Delivery under UAS Traffic Management Environment
Aerospace 2020, 7(10), 140; https://doi.org/10.3390/aerospace7100140 - 25 Sep 2020
Cited by 5 | Viewed by 1938
Abstract
Resulting from a mature accomplishment of the unmanned aircraft system (UAS), it is feasible to be adopted into logistic delivery services. The supporting technologies should be identified and examined, accompanying with the risk assessment. This paper surveys the risk assessment studies for UAVs. [...] Read more.
Resulting from a mature accomplishment of the unmanned aircraft system (UAS), it is feasible to be adopted into logistic delivery services. The supporting technologies should be identified and examined, accompanying with the risk assessment. This paper surveys the risk assessment studies for UAVs. The expected level of safety (ELS) analysis is a key factor to safety concerns. By introducing the UTM infrastructure, the UAS implementation can be monitored. From the NASA technical capability level (TCL), UAV in beyond visual line of sight (BVLOS) flights would need certain verifications. Two UAS logistic delivery case studies are tested to assert the UAS services. To examine the ELS to ground risk and air risk, the case studies result in acceptable data to support the UAS logistic delivery with adequate path planning in the remote and suburban areas in Taiwan. Full article
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Article
Pareto Optimal PID Tuning for Px4-Based Unmanned Aerial Vehicles by Using a Multi-Objective Particle Swarm Optimization Algorithm
Aerospace 2020, 7(6), 71; https://doi.org/10.3390/aerospace7060071 - 04 Jun 2020
Cited by 7 | Viewed by 3427
Abstract
Unmanned aerial vehicles (UAVs) are affordable these days. For that reason, there are currently examples of the use of UAVs in recreational, professional and research applications. Most of the commercial UAVs use Px4 for their operating system. Even though Px4 allows one to [...] Read more.
Unmanned aerial vehicles (UAVs) are affordable these days. For that reason, there are currently examples of the use of UAVs in recreational, professional and research applications. Most of the commercial UAVs use Px4 for their operating system. Even though Px4 allows one to change the flight controller structure, the proportional-integral-derivative (PID) format is still by far the most popular choice. A selection of the PID controller parameters is required before the UAV can be used. Although there are guidelines for the design of PID parameters, they do not guarantee the stability of the UAV, which in many cases, leads to collisions involving the UAV during the calibration process. In this paper, an offline tuning procedure based on the multi-objective particle swarm optimization (MOPSO) algorithm for the attitude and altitude control of a Px4-based UAV is proposed. A Pareto dominance concept is used for the MOPSO to find values for the PID comparing parameters of step responses (overshoot, rise time and root-mean-square). Experimental results are provided to validate the proposed tuning procedure by using a quadrotor as a case study. Full article
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2019

Jump to: 2022, 2021, 2020, 2018, 2017, 2016, 2015

Article
A Virtual Test Bench of a Parallel Hybrid Propulsion System for UAVs
Aerospace 2019, 6(7), 77; https://doi.org/10.3390/aerospace6070077 - 02 Jul 2019
Cited by 5 | Viewed by 3464
Abstract
The article proposes the design of a test bench simulator to test a parallel hybrid propulsion architecture for aeronautical applications. The virtual test bench simulates, in a scaled version, the real test bench, designed for a power of about 0.4 MW. After presenting [...] Read more.
The article proposes the design of a test bench simulator to test a parallel hybrid propulsion architecture for aeronautical applications. The virtual test bench simulates, in a scaled version, the real test bench, designed for a power of about 0.4 MW. After presenting the architecture of the real propulsion system, the virtual test bench is described. The real system is basically composed by a paralleled electric motor and thermal engine which provide mechanical power to the propeller. Saving cost and volume the test bench is composed by electric motors simulates the behaviors of the real propulsion system despite their differences. The dynamic relationships expressing the transmission of torque between the components, and the method of down-sizing the power delivered are highlighted. Particular attention is given to the real inertia actions that must be simulated on the virtual test bench. An application of the proposed methodology is then presented through the simulation of the take-off phase, and the torque time histories, angular velocities and powers generated on the virtual test bench are used to verify the corresponding time histories expected in the real system. Full article
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Article
Investigation of Micro Gas Turbine Systems for High Speed Long Loiter Tactical Unmanned Air Systems
Aerospace 2019, 6(5), 55; https://doi.org/10.3390/aerospace6050055 - 14 May 2019
Cited by 15 | Viewed by 3712
Abstract
In this study, the on-going research into the improvement of micro-gas turbine propulsion system performance and the suitability for its application as propulsion systems for small tactical UAVs (<600 kg) is investigated. The study is focused around the concept of converting existing micro [...] Read more.
In this study, the on-going research into the improvement of micro-gas turbine propulsion system performance and the suitability for its application as propulsion systems for small tactical UAVs (<600 kg) is investigated. The study is focused around the concept of converting existing micro turbojet engines into turbofans with the use of a continuously variable gearbox, thus maintaining a single spool configuration and relative design simplicity. This is an effort to reduce the initial engine development cost, whilst improving the propulsive performance. The BMT 120 KS micro turbojet engine is selected for the performance evaluation of the conversion process using the gas turbine performance software GasTurb13. The preliminary design of a matched low-pressure compressor (LPC) for the proposed engine is then performed using meanline calculation methods. According to the analysis that is carried out, an improvement in the converted micro gas turbine engine performance, in terms of thrust and specific fuel consumption is achieved. Furthermore, with the introduction of a CVT gearbox, the fan speed operation may be adjusted independently of the core, allowing an increased thrust generation or better fuel consumption. This therefore enables a wider gamut of operating conditions and enhances the performance and scope of the tactical UAV. Full article
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2018

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Article
Robust Full Tracking Control Design of Disturbed Quadrotor UAVs with Unknown Dynamics
Aerospace 2018, 5(4), 115; https://doi.org/10.3390/aerospace5040115 - 30 Oct 2018
Cited by 7 | Viewed by 3739
Abstract
In this study, we develop a rigorous tracking control approach for quadrotor unmanned aerial vehicles (UAVs) with unknown dynamics, unknown physical parameters, and subject to unknown and unpredictable disturbances. In order to better estimate the unknown functions, seven interval type-2-adaptive fuzzy systems (IT2-AFSs) [...] Read more.
In this study, we develop a rigorous tracking control approach for quadrotor unmanned aerial vehicles (UAVs) with unknown dynamics, unknown physical parameters, and subject to unknown and unpredictable disturbances. In order to better estimate the unknown functions, seven interval type-2-adaptive fuzzy systems (IT2-AFSs) and five adaptive systems are designed. Then, a new IT2 adaptive fuzzy reaching sliding mode system (IT2-AFRSMS) which generates an optimal smooth adaptive fuzzy reaching sliding mode control law (AFRSMCL) using IT2-AFSs is introduced. The AFRSMCL is designed a way that ensures that its gains are efficiently estimated. Thus, the global proposed control law can effectively achieve the predetermined performances of the tracking control while simultaneously avoiding the chattering phenomenon, despite the approximation errors and all disturbances acting on the quadrotor dynamics. The adaptation laws are designed by utilizing the stability analysis of Lyapunov. A simulation example is used to validate the robustness and effectiveness of the proposed method of control. The obtained results confirm the results of the mathematical analysis in guaranteeing the tracking convergence and stability of the closed loop dynamics despite the unknown dynamics, unknown disturbances, and unknown physical parameters of the controlled system. Full article
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Article
Experimental Control of Two Connected Fixed Wing Aircraft
Aerospace 2018, 5(4), 113; https://doi.org/10.3390/aerospace5040113 - 28 Oct 2018
Cited by 6 | Viewed by 3273
Abstract
This paper investigates the design and flight test of two fixed wing aircraft connected at the wing tips. Connecting multiple aircraft introduces flexible modes into a typically rigid body system. These flexible modes make manual control of the entire system extremely difficult if [...] Read more.
This paper investigates the design and flight test of two fixed wing aircraft connected at the wing tips. Connecting multiple aircraft introduces flexible modes into a typically rigid body system. These flexible modes make manual control of the entire system extremely difficult if not impossible. An autopilot system that seeks to keep this aircraft system wings level and a constant pitch angle is investigated here. The autopilot system is shown to work in an example simulation for a two body aircraft connected at the wing tips. An experimental aircraft system is also designed, built and flown with reasonable success proving the implementation of said controller on a real system. Full article
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Article
Fast and Robust Flight Altitude Estimation of Multirotor UAVs in Dynamic Unstructured Environments Using 3D Point Cloud Sensors
Aerospace 2018, 5(3), 94; https://doi.org/10.3390/aerospace5030094 - 06 Sep 2018
Cited by 8 | Viewed by 3629
Abstract
This paper presents a fast and robust approach for estimating the flight altitude of multirotor Unmanned Aerial Vehicles (UAVs) using 3D point cloud sensors in cluttered, unstructured, and dynamic indoor environments. The objective is to present a flight altitude estimation algorithm, replacing the [...] Read more.
This paper presents a fast and robust approach for estimating the flight altitude of multirotor Unmanned Aerial Vehicles (UAVs) using 3D point cloud sensors in cluttered, unstructured, and dynamic indoor environments. The objective is to present a flight altitude estimation algorithm, replacing the conventional sensors such as laser altimeters, barometers, or accelerometers, which have several limitations when used individually. Our proposed algorithm includes two stages: in the first stage, a fast clustering of the measured 3D point cloud data is performed, along with the segmentation of the clustered data into horizontal planes. In the second stage, these segmented horizontal planes are mapped based on the vertical distance with respect to the point cloud sensor frame of reference, in order to provide a robust flight altitude estimation even in presence of several static as well as dynamic ground obstacles. We validate our approach using the IROS 2011 Kinect dataset available in the literature, estimating the altitude of the RGB-D camera using the provided 3D point clouds. We further validate our approach using a point cloud sensor on board a UAV, by means of several autonomous real flights, closing its altitude control loop using the flight altitude estimated by our proposed method, in presence of several different static as well as dynamic ground obstacles. In addition, the implementation of our approach has been integrated in our open-source software framework for aerial robotics called Aerostack. Full article
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Article
Multi-UAV Doppler Information Fusion for Target Tracking Based on Distributed High Degrees Information Filters
Aerospace 2018, 5(1), 28; https://doi.org/10.3390/aerospace5010028 - 08 Mar 2018
Cited by 12 | Viewed by 4505
Abstract
Multi-Unmanned Aerial Vehicle (UAV) Doppler-based target tracking has not been widely investigated, specifically when using modern nonlinear information filters. A high-degree Gauss–Hermite information filter, as well as a seventh-degree cubature information filter (CIF), is developed to improve the fifth-degree and third-degree CIFs proposed [...] Read more.
Multi-Unmanned Aerial Vehicle (UAV) Doppler-based target tracking has not been widely investigated, specifically when using modern nonlinear information filters. A high-degree Gauss–Hermite information filter, as well as a seventh-degree cubature information filter (CIF), is developed to improve the fifth-degree and third-degree CIFs proposed in the most recent related literature. These algorithms are applied to maneuvering target tracking based on Radar Doppler range/range rate signals. To achieve this purpose, different measurement models such as range-only, range rate, and bearing-only tracking are used in the simulations. In this paper, the mobile sensor target tracking problem is addressed and solved by a higher-degree class of quadrature information filters (HQIFs). A centralized fusion architecture based on distributed information filtering is proposed, and yielded excellent results. Three high dynamic UAVs are simulated with synchronized Doppler measurement broadcasted in parallel channels to the control center for global information fusion. Interesting results are obtained, with the superiority of certain classes of higher-degree quadrature information filters. Full article
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2017

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Article
Experimental Investigation of the Wake and the Wingtip Vortices of a UAV Model
Aerospace 2017, 4(4), 53; https://doi.org/10.3390/aerospace4040053 - 01 Nov 2017
Cited by 9 | Viewed by 6419
Abstract
An experimental investigation of the wake of an Unmanned Aerial Vehicle (UAV) model using flow visualization techniques and a 3D Laser Doppler Anemometry (LDA) system is presented in this work. Emphasis is given on the flow field at the wingtip and the investigation [...] Read more.
An experimental investigation of the wake of an Unmanned Aerial Vehicle (UAV) model using flow visualization techniques and a 3D Laser Doppler Anemometry (LDA) system is presented in this work. Emphasis is given on the flow field at the wingtip and the investigation of the tip vortices. A comparison of the velocity field is made with and without winglet devices installed at the wingtips. The experiments are carried out in a closed-circuit subsonic wind tunnel. The flow visualization techniques include smoke-wire and smoke-probe experiments to identify the flow phenomena, whereas for accurately measuring the velocity field point measurements are conducted using the LDA system. Apart from the measured velocities, vorticity and circulation quantities are also calculated and compared for the two cases. The results help to provide a more detailed view of the flow field around the UAV and indicate the winglets’ significant contribution to the deconstruction of wing-tip vortex structures. Full article
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Article
Aerial Target Tracking Algorithm Based on Faster R-CNN Combined with Frame Differencing
Aerospace 2017, 4(2), 32; https://doi.org/10.3390/aerospace4020032 - 20 Jun 2017
Cited by 6 | Viewed by 5418
Abstract
We propose a robust approach to detecting and tracking moving objects for a naval unmanned aircraft system (UAS) landing on an aircraft carrier. The frame difference algorithm follows a simple principle to achieve real-time tracking, whereas Faster Region-Convolutional Neural Network (R-CNN) performs highly [...] Read more.
We propose a robust approach to detecting and tracking moving objects for a naval unmanned aircraft system (UAS) landing on an aircraft carrier. The frame difference algorithm follows a simple principle to achieve real-time tracking, whereas Faster Region-Convolutional Neural Network (R-CNN) performs highly precise detection and tracking characteristics. We thus combine Faster R-CNN with the frame difference method, which is demonstrated to exhibit robust and real-time detection and tracking performance. In our UAS landing experiments, two cameras placed on both sides of the runway are used to capture the moving UAS. When the UAS is captured, the joint algorithm uses frame difference to detect the moving target (UAS). As soon as the Faster R-CNN algorithm accurately detects the UAS, the detection priority is given to Faster R-CNN. In this manner, we also perform motion segmentation and object detection in the presence of changes in the environment, such as illumination variation or “walking persons”. By combining the 2 algorithms we can accurately detect and track objects with a tracking accuracy rate of up to 99% and a frame per second of up to 40 Hz. Thus, a solid foundation is laid for subsequent landing guidance. Full article
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Article
Nonlinear Model Predictive Control for Unmanned Aerial Vehicles
Aerospace 2017, 4(2), 31; https://doi.org/10.3390/aerospace4020031 - 17 Jun 2017
Cited by 39 | Viewed by 5531
Abstract
This paper discusses the derivation and implementation of a nonlinear model predictive control law for tracking reference trajectories and constrained control of a quadrotor platform. The approach uses the state-dependent coefficient form to capture the system nonlinearities into a pseudo-linear system matrix. The [...] Read more.
This paper discusses the derivation and implementation of a nonlinear model predictive control law for tracking reference trajectories and constrained control of a quadrotor platform. The approach uses the state-dependent coefficient form to capture the system nonlinearities into a pseudo-linear system matrix. The state-dependent coefficient form is derived following a rigorous analysis of aerial vehicle dynamics that systematically accounts for the peculiarities of such systems. The same state-dependent coefficient form is exploited for obtaining a nonlinear equivalent of the model predictive control. The nonlinear model predictive control law is derived by first transforming the continuous system into a sampled-data form and and then using a sequential quadratic programming solver while accounting for input, output and state constraints. The boundedness of the tracking errors using the sampled-data implementation is shown explicitly. The performance of the nonlinear controller is illustrated through representative simulations showing the tracking of several aggressive reference trajectories with and without disturbances. Full article
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Article
Stochastic Trajectory Generation Using Particle Swarm Optimization for Quadrotor Unmanned Aerial Vehicles (UAVs)
Aerospace 2017, 4(2), 27; https://doi.org/10.3390/aerospace4020027 - 08 May 2017
Cited by 17 | Viewed by 7167
Abstract
The aim of this paper is to provide a realistic stochastic trajectory generation method for unmanned aerial vehicles that offers a tool for the emulation of trajectories in typical flight scenarios. Three scenarios are defined in this paper. The trajectories for these scenarios [...] Read more.
The aim of this paper is to provide a realistic stochastic trajectory generation method for unmanned aerial vehicles that offers a tool for the emulation of trajectories in typical flight scenarios. Three scenarios are defined in this paper. The trajectories for these scenarios are implemented with quintic B-splines that grant smoothness in the second-order derivatives of Euler angles and accelerations. In order to tune the parameters of the quintic B-spline in the search space, a multi-objective optimization method called particle swarm optimization (PSO) is used. The proposed technique satisfies the constraints imposed by the configuration of the unmanned aerial vehicle (UAV). Further particular constraints can be introduced such as: obstacle avoidance, speed limitation, and actuator torque limitations due to the practical feasibility of the trajectories. Finally, the standard rapidly-exploring random tree (RRT*) algorithm, the standard (A*) algorithm and the genetic algorithm (GA) are simulated to make a comparison with the proposed algorithm in terms of execution time and effectiveness in finding the minimum length trajectory. Full article
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Article
Direct Entry Minimal Path UAV Loitering Path Planning
Aerospace 2017, 4(2), 23; https://doi.org/10.3390/aerospace4020023 - 18 Apr 2017
Cited by 1 | Viewed by 4829
Abstract
Fixed Wing Unmanned Aerial Vehicles (UAVs) performing Intelligence, Surveillance and Reconnaissance (ISR) typically fly over Areas of Interest (AOIs) to collect sensor data of the ground from the air. If needed, the traditional method of extending sensor collection time is to loiter or [...] Read more.
Fixed Wing Unmanned Aerial Vehicles (UAVs) performing Intelligence, Surveillance and Reconnaissance (ISR) typically fly over Areas of Interest (AOIs) to collect sensor data of the ground from the air. If needed, the traditional method of extending sensor collection time is to loiter or turn circularly around the center of an AOI. Current Autopilot systems on small UAVs can be limited in their feature set and typically follow a waypoint chain system that allows for loitering, but requires that the center of the AOI to be traversed which may produce unwanted turns outside of the AOI before entering the loiter. An investigation was performed to compare the current loitering techniques against two novel smart loitering methods. The first method investigated, Tangential Loitering Path Planner (TLPP), utilized paths tangential to the AOIs to enter and exit efficiently, eliminating unnecessary turns outside of the AOI. The second method, Least Distance Loitering Path Planner (LDLPP), utilized four unique flight maneuvers that reduce transit distances while eliminating unnecessary turns outside of the AOI present in the TLPP method. Simulation results concluded that the Smart Loitering Methods provide better AOI coverage during six mission scenarios. It was also determined that the LDLPP method spends less time in transit between AOIs. The reduction in required transit time could be used for surveying additional AOIs. Full article
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Technical Note
Perpetual Solar-Powered Flight across Regions around the World for a Year-Long Operation
Aerospace 2017, 4(2), 20; https://doi.org/10.3390/aerospace4020020 - 11 Apr 2017
Cited by 7 | Viewed by 4190
Abstract
This study aims to promote the conventional solar-powered unmanned aerial vehicle (UAV) to be used as a satellite known as a pseudo-satellite (pseudolite). The applications of UAV as a satellite are still in the initial stages because these proposed UAVs are required to [...] Read more.
This study aims to promote the conventional solar-powered unmanned aerial vehicle (UAV) to be used as a satellite known as a pseudo-satellite (pseudolite). The applications of UAV as a satellite are still in the initial stages because these proposed UAVs are required to fly for long hours at a specified altitude. Any solar-powered system requires extensive mission operation planning to ensure sufficient power to sustain a level flight. This study simulates the optimal UAV configurations at various global locations, and determines the feasibility of a solar-powered UAV to sustain a continuous mission. This study is divided into two different phases. An all-year operation of the average UAV (AVUAV) is simulated in Phase One and is designed specifically for each of 12 cities, namely, Ottawa, Honolulu, Quito, Tahiti, Brasilia, London, Riyadh, Tokyo, Kuala Lumpur, Accra, Port Louis, and Suva. Phase Two is a simulation of a solar-powered UAV design model known as 1UAV, applicable to any city around the world for a year-long flight. The findings state that a single UAV design is sufficient to operate continuously around the world if its detailed mission path planning has been defined. Full article
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Technical Note
3D CFD Simulation and Experimental Validation of Small APC Slow Flyer Propeller Blade
Aerospace 2017, 4(1), 10; https://doi.org/10.3390/aerospace4010010 - 25 Feb 2017
Cited by 38 | Viewed by 7617
Abstract
The current work presents the numerical prediction method to determine small-scale propeller performance. The study is implemented using the commercially available computational fluid dynamics (CFD) solver, FLUENT. Numerical results are compared with the available experimental data for an advanced precision composites (APC) Slow [...] Read more.
The current work presents the numerical prediction method to determine small-scale propeller performance. The study is implemented using the commercially available computational fluid dynamics (CFD) solver, FLUENT. Numerical results are compared with the available experimental data for an advanced precision composites (APC) Slow Flyer propeller blade to determine the discrepancy of the thrust coefficient, power coefficient, and efficiencies. The study utilized unstructured tetrahedron meshing throughout the analysis, with a standard k-ω turbulence model. The Multiple Reference Frame model was also used to consider the rotation of the propeller toward its local reference frame at 3008 revolutions per minute (RPM). Results show reliable thrust coefficient, power coefficient, and efficiency data for the case of low advance ratio and an advance ratio less than the negative thrust conditions. Full article
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Article
Trajectory Tracking of a Tri-Rotor Aerial Vehicle Using an MRAC-Based Robust Hybrid Control Algorithm
Aerospace 2017, 4(1), 3; https://doi.org/10.3390/aerospace4010003 - 19 Jan 2017
Cited by 5 | Viewed by 5272
Abstract
In this paper, a novel Model Reference Adaptive Control (MRAC)-based hybrid control algorithm is presented for the trajectory tracking of a tri-rotor Unmanned Aerial Vehicle (UAV). The mathematical model of the tri-rotor is based on the Newton–Euler formula, whereas the MRAC-based hybrid controller [...] Read more.
In this paper, a novel Model Reference Adaptive Control (MRAC)-based hybrid control algorithm is presented for the trajectory tracking of a tri-rotor Unmanned Aerial Vehicle (UAV). The mathematical model of the tri-rotor is based on the Newton–Euler formula, whereas the MRAC-based hybrid controller consists of Fuzzy Proportional Integral Derivative (F-PID) and Fuzzy Proportional Derivative (F-PD) controllers. MRAC is used as the main controller for the dynamics, while the parameters of the adaptive controller are fine-tuned by the F-PD controller for the altitude control subsystem and the F-PID controller for the attitude control subsystem of the UAV. The stability of the system is ensured and proven by Lyapunov stability analysis. The proposed control algorithm is tested and verified using computer simulations for the trajectory tracking of the desired path as an input. The effectiveness of our proposed algorithm is compared with F-PID and the Fuzzy Logic Controller (FLC). Our proposed controller exhibits much less steady state error, quick error convergence in the presence of disturbance or noise, and model uncertainties. Full article
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2016

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Article
Analysis of Pilot-Induced-Oscillation and Pilot Vehicle System Stability Using UAS Flight Experiments
Aerospace 2016, 3(4), 42; https://doi.org/10.3390/aerospace3040042 - 29 Nov 2016
Cited by 9 | Viewed by 4769
Abstract
This paper reports the results of a Pilot-Induced Oscillation (PIO) and human pilot control characterization study performed using flight data collected with a Remotely Controlled (R/C) unmanned research aircraft. The study was carried out on the longitudinal axis of the aircraft. Several existing [...] Read more.
This paper reports the results of a Pilot-Induced Oscillation (PIO) and human pilot control characterization study performed using flight data collected with a Remotely Controlled (R/C) unmanned research aircraft. The study was carried out on the longitudinal axis of the aircraft. Several existing Category 1 and Category 2 PIO criteria developed for manned aircraft are first surveyed and their effectiveness for predicting the PIO susceptibility for the R/C unmanned aircraft is evaluated using several flight experiments. It was found that the Bandwidth/Pitch rate overshoot and open loop onset point (OLOP) criteria prediction results matched flight test observations. However, other criteria failed to provide accurate prediction results. To further characterize the human pilot control behavior during these experiments, a quasi-linear pilot model is used. The parameters of the pilot model estimated using data obtained from flight tests are then used to obtain information about the stability of the Pilot Vehicle System (PVS) for Category 1 PIOs occurred during straight and level flights. The batch estimation technique used to estimate the parameters of the quasi-linear pilot model failed to completely capture the compatibility nature of the human pilot. The estimation results however provided valuable insights into the frequency characteristics of the human pilot commands. Additionally, stability analysis of the Category 2 PIOs for elevator actuator rate limiting is carried out using simulations and the results are compared with actual flight results. Full article
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Communication
Effect of Leading-Edge Slats at Low Reynolds Numbers
Aerospace 2016, 3(4), 39; https://doi.org/10.3390/aerospace3040039 - 17 Nov 2016
Cited by 2 | Viewed by 6424
Abstract
One of the most commonly implemented devices for stall control on wings and airfoils is a leading-edge slat. While functioning of slats at high Reynolds number is well documented, this is not the case at the low Reynolds numbers common for small unmanned [...] Read more.
One of the most commonly implemented devices for stall control on wings and airfoils is a leading-edge slat. While functioning of slats at high Reynolds number is well documented, this is not the case at the low Reynolds numbers common for small unmanned aerial vehicles. Consequently, a low-speed wind tunnel investigation was undertaken to elucidate the performance of a slat at Re = 250,000. Force balance measurements accompanied by surface flow visualization images are presented. The slat extension and rotation was varied and documented. The results indicate that for small slat extensions, slat rotation is deleterious to performance, but is required for larger slat extensions for effective lift augmentation. Deployment of the slat was accompanied by a significant drag penalty due to premature localized flow separation. Full article
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Article
An Empirical Study of Overlapping Rotor Interference for a Small Unmanned Aircraft Propulsion System
Aerospace 2016, 3(4), 32; https://doi.org/10.3390/aerospace3040032 - 10 Oct 2016
Cited by 24 | Viewed by 4938
Abstract
The majority of research into full-sized helicopter overlapping propulsion systems involves co-axial setups (fully overlapped). Partially overlapping rotor setups (tandem, multirotor) have received less attention, and empirical data produced over the years is limited. The increase in demand for compact small unmanned aircraft [...] Read more.
The majority of research into full-sized helicopter overlapping propulsion systems involves co-axial setups (fully overlapped). Partially overlapping rotor setups (tandem, multirotor) have received less attention, and empirical data produced over the years is limited. The increase in demand for compact small unmanned aircraft has exposed the need for empirical investigations of overlapping propulsion systems at a small scale (Reynolds Number < 250,000). Rotor-to-rotor interference at the static state in various overlapping propulsion system configurations was empirically measured using off the shelf T-Motor 16 inch × 5.4 inch rotors. A purpose-built test rig was manufactured allowing various overlapping rotor configurations to be tested. First, single rotor data was gathered, then performance measurements were taken at different thrust and tip speeds on a range of overlap configurations. The studies were conducted in a system torque balance mode. Overlapping rotor performance was compared to an isolated dual rotor propulsion system revealing interference factors which were compared to the momentum theory. Tests revealed that in the co-axial torque-balanced propulsion system the upper rotor outperforms the lower rotor at axial separation ratios between 0.05 and 0.85. Additionally, in the same region, thrust sharing between the two rotors changed by 21%; the upper rotor produced more thrust than the lower rotor at all times. Peak performance was recorded as a 22% efficiency loss when the axial separation ratio was greater than 0.25. The performance of a co-axial torque-balanced system reached a 27% efficiency loss when the axial separation ratio was equal to 0.05. The co-axial system swirl recovery effect was recorded to have a 4% efficiency gain in the axial separation ratio region between 0.05 and 0.85. The smallest efficiency loss (3%) was recorded when the rotor separation ratio was between 0.95 and 1 (axial separation ratio was kept at 0.05). Tests conducted at a rotor separation ratio of 0.85 showed that the efficiency loss decreased when the axial separation ratio was greater than 0.25. The lower rotor outperformed the upper rotor in the rotor separation ratio region from 0.95 to 1 (axial separation ratio was kept at 0.05) at an overall system thrust of 8 N, and matched the upper rotor performance at the tested overall thrust of 15 N. Full article
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Review
Bio-Inspired Principles Applied to the Guidance, Navigation and Control of UAS
Aerospace 2016, 3(3), 21; https://doi.org/10.3390/aerospace3030021 - 20 Jul 2016
Cited by 12 | Viewed by 5691
Abstract
This review describes a number of biologically inspired principles that have been applied to the visual guidance, navigation and control of Unmanned Aerial System (UAS). The current limitations of UAS systems are outlined, such as the over-reliance on GPS, the requirement for more [...] Read more.
This review describes a number of biologically inspired principles that have been applied to the visual guidance, navigation and control of Unmanned Aerial System (UAS). The current limitations of UAS systems are outlined, such as the over-reliance on GPS, the requirement for more self-reliant systems and the need for UAS to have a greater understanding of their environment. It is evident that insects, even with their small brains and limited intelligence, have overcome many of the shortcomings of the current state of the art in autonomous aerial guidance. This has motivated research into bio-inspired systems and algorithms, specifically vision-based navigation, situational awareness and guidance. Full article
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Article
A Shape Memory Alloy Application for Compact Unmanned Aerial Vehicles
Aerospace 2016, 3(2), 16; https://doi.org/10.3390/aerospace3020016 - 31 May 2016
Cited by 13 | Viewed by 5623
Abstract
Shape memory alloys materials, SMA, offer several advantages that designers can rely on such as the possibility of transmitting large forces and deformations, compactness, and the intrinsic capability to absorb loads. Their use as monolithic actuators, moreover, can lead to potential simplifications of [...] Read more.
Shape memory alloys materials, SMA, offer several advantages that designers can rely on such as the possibility of transmitting large forces and deformations, compactness, and the intrinsic capability to absorb loads. Their use as monolithic actuators, moreover, can lead to potential simplifications of the system, through a reduction of number of parts and the removal of many free play gaps among mechanics. For these reasons, technological aerospace research is focusing on this kind of technology more and more, even though fatigue life, performance degradation, and other issues are still open. In the work at hand, landing gear for unmanned aerial vehicles, UAV, is presented, integrated with shape memory alloys springs as actuation devices. A conceptual prototype has been realized to verify the system ability in satisfying specs, in terms of deployment and retraction capability. Starting from the proposed device working principle and the main design parameters identification, the design phase is faced, setting those parameters to meet weight, deployment angle, energy consumption, and available room requirements. Then, system modeling and performance prediction is performed and finally a correlation between numerical and experimental results is presented. Full article
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Article
Fixed-Wing UAV Attitude Estimation Using Single Antenna GPS Signal Strength Measurements
Aerospace 2016, 3(2), 14; https://doi.org/10.3390/aerospace3020014 - 13 May 2016
Cited by 9 | Viewed by 4821
Abstract
This article considers a novel approach to using global positioning system (GPS) signal strength readings and estimated velocity vector for estimating the attitude of a small fixed-wing unmanned aerial vehicle (UAV). This approach has the benefit being able to estimate full position, velocity [...] Read more.
This article considers a novel approach to using global positioning system (GPS) signal strength readings and estimated velocity vector for estimating the attitude of a small fixed-wing unmanned aerial vehicle (UAV). This approach has the benefit being able to estimate full position, velocity and attitude states of a UAV using only the data from a single GPS receiver and antenna. Two different approaches for utilizing GPS signal strength within measurement updates for UAV attitude in a nonlinear Kalman filter are discussed and assessed using recorded UAV flight data. Comparisons of UAV pitch and roll estimates against measurements from a high-grade mechanical gyroscope are used to show that approximately 5° error with respect to both mean and standard-deviation on both axes is achievable. Full article
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Article
Guidance, Navigation and Control of Unmanned Airships under Time-Varying Wind for Extended Surveillance
Aerospace 2016, 3(1), 8; https://doi.org/10.3390/aerospace3010008 - 17 Feb 2016
Cited by 14 | Viewed by 4720
Abstract
This paper deals with the control of lighter-than-air vehicles, more specifically the design of an integrated guidance, navigation and control (GNC) scheme that is capable of navigating an airship through a series of constant-altitude, planar waypoints. Two guidance schemes are introduced, a track-specific [...] Read more.
This paper deals with the control of lighter-than-air vehicles, more specifically the design of an integrated guidance, navigation and control (GNC) scheme that is capable of navigating an airship through a series of constant-altitude, planar waypoints. Two guidance schemes are introduced, a track-specific guidance law and a proportional navigation guidance law, that provide the required signals to the corresponding controllers based on the airship position relative to a target waypoint. A novel implementation of the extended Kalman filter, namely the scheduled extended Kalman filter, estimates the required states and wind speed to enhance the performance of the track-specific guidance law in the presence of time-varying wind. The performance of the GNC system is tested using a high fidelity nonlinear dynamic simulation for a variety of flying conditions. Representative results illustrate the performance of the integrated system for chosen flight conditions. Full article
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Article
Turbulence Effects on Modified State Observer-Based Adaptive Control: Black Kite Micro Aerial Vehicle
Aerospace 2016, 3(1), 6; https://doi.org/10.3390/aerospace3010006 - 05 Feb 2016
Cited by 1 | Viewed by 4074
Abstract
This paper presents the implementation of a modified state observer-based adaptive dynamic inverse controller for the Black Kite micro aerial vehicle. The pitch and velocity adaptations are computed by the modified state observer in the presence of turbulence to simulate atmospheric conditions. This [...] Read more.
This paper presents the implementation of a modified state observer-based adaptive dynamic inverse controller for the Black Kite micro aerial vehicle. The pitch and velocity adaptations are computed by the modified state observer in the presence of turbulence to simulate atmospheric conditions. This state observer uses the estimation error to generate the adaptations and, hence, is more robust than model reference adaptive controllers which use modeling or tracking error. In prior work, a traditional proportional-integral-derivative control law was tested in simulation for its adaptive capability in the longitudinal dynamics of the Black Kite micro aerial vehicle. This controller tracks the altitude and velocity commands during normal conditions, but fails in the presence of both parameter uncertainties and system failures. The modified state observer-based adaptations, along with the proportional-integral-derivative controller enables tracking despite these conditions. To simulate flight of the micro aerial vehicle with turbulence, a Dryden turbulence model is included. The turbulence levels used are based on the absolute load factor experienced by the aircraft. The length scale was set to 2.0 meters with a turbulence intensity of 5.0 m/s that generates a moderate turbulence. Simulation results for various flight conditions show that the modified state observer-based adaptations were able to adapt to the uncertainties and the controller tracks the commanded altitude and velocity. The summary of results for all of the simulated test cases and the response plots of various states for typical flight cases are presented. Full article
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Article
Target Tracking in 3-D Using Estimation Based Nonlinear Control Laws for UAVs
Aerospace 2016, 3(1), 5; https://doi.org/10.3390/aerospace3010005 - 01 Feb 2016
Cited by 9 | Viewed by 4611
Abstract
This paper presents an estimation based backstepping like control law design for an Unmanned Aerial Vehicle (UAV) to track a moving target in 3-D space. A ground-based sensor or an onboard seeker antenna provides range, azimuth angle, and elevation angle measurements to a [...] Read more.
This paper presents an estimation based backstepping like control law design for an Unmanned Aerial Vehicle (UAV) to track a moving target in 3-D space. A ground-based sensor or an onboard seeker antenna provides range, azimuth angle, and elevation angle measurements to a chaser UAV that implements an extended Kalman filter (EKF) to estimate the full state of the target. A nonlinear controller then utilizes this estimated target state and the chaser’s state to provide speed, flight path, and course/heading angle commands to the chaser UAV. Tracking performance with respect to measurement uncertainty is evaluated for three cases: (1) stationary white noise; (2) stationary colored noise and (3) non-stationary (range correlated) white noise. Furthermore, in an effort to improve tracking performance, the measurement model is made more realistic by taking into consideration range-dependent uncertainties in the measurements, i.e., as the chaser closes in on the target, measurement uncertainties are reduced in the EKF, thus providing the UAV with more accurate control commands. Simulation results for these cases are shown to illustrate target state estimation and trajectory tracking performance. Full article
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