Authors:Ziqing Ma, Ewoud J.J. Smeur, Guido C.H.E. de Croon Abstract: International Journal of Micro Air Vehicles, Volume 14, Issue , January-December 2022. Tailsitters have complex aerodynamics that make them hard to control throughout the entire flight envelope, especially at very high angle of attack (AoA) and reverse flow conditions. The development of controllers for these vehicles is hampered by the absence of publicly available data on forces and moments experienced in such conditions. In this paper, wind tunnel experiments are performed under different flap deflections and throttle settings at all possible AoA. The dataset is made open access. Our analysis of the data shows for the tested wing, flap deflections greatly affect the lift coefficient and stall occurs at [math] AoA as well as [math]. Wing-propeller interaction is studied by analyzing the propeller induced force in the axis orthogonal to the thrust axis, which is dependent on AoA, airspeed, flap deflections and thrust in a nonlinear and coupled manner. The influence of inverse flow on the wing is also discussed: The data confirm that when the airflow over the wing is reversed, flap deflections will affect the pitch moment in an opposite way compared to the non-reversed case, but this opposite effect can be avoided by increasing the throttle setting. The data show the exact relationship between flap deflections and forces in this condition. Moreover, it is found that the flap control effectiveness for a wing with or without spinning propellers is usually higher around zero degrees AoA than at [math] and it is more effective to change the flaps from [math] to [math] than from [math] to the respective [math]. Citation: International Journal of Micro Air Vehicles PubDate: 2022-07-06T01:38:57Z DOI: 10.1177/17568293221110931 Issue No:Vol. 14 (2022)
Authors:Oghuz Bektash, Jacob Juul Naundrup, Anders la Cour-Harbo Abstract: International Journal of Micro Air Vehicles, Volume 14, Issue , January-December 2022. Autonomous landing is a fundamental aspect of drone operations which is being focused upon by the industry, with ever-increasing demands on safety. As the drones are likely to become indispensable vehicles in near future, they are expected to succeed in automatically recognizing a landing spot from the nearby points, maneuvering toward it, and ultimately, performing a safe landing. Accordingly, this paper investigates the idea of vision-based location detection on the ground for an automated emergency response system which can continuously monitor the environment and spot safe places when needed. A convolutional neural network which learns from image-based feature representation at multiple scales is introduced. The model takes the ground images, assign significance to various aspects in them and recognize the landing spots. The results provided support for the model, with accurate classification of ground image according to their visual content. They also demonstrate the feasibility of computationally inexpensive implementation of the model on a small computer that can be easily embedded on a drone. Citation: International Journal of Micro Air Vehicles PubDate: 2022-06-30T06:31:23Z DOI: 10.1177/17568293221106492 Issue No:Vol. 14 (2022)
Authors:Jolan Wauters Abstract: International Journal of Micro Air Vehicles, Volume 14, Issue , January-December 2022. In this paper the design optimization-under-uncertainty of a forward swept wing (FSW) blended wing body (BWB) unmanned aerial vehicle (UAV) is examined. Conventional BWBs are often tailless, which leads to a backward swept wing to ensure longitudinal static stability. This in turn can induce flow separation at the tip, leading to a loss of lift, controllability and the appearance of a nose-up pitching moment. A possible solution to this problem is a conceptual redesign by introducing a forward swept wing, which is inherently free of tip-stall, but needs a careful design in order to be controllable. However, fixed wing UAVs are often produced by means of direct injection expanded foam moulding, which is characterized by not negligible production tolerances. This lead to a reliability-based robust design optimization problem, for which a novel framework is employed: SAMURAI. Firstly, the method accounts for computational cost by means of surrogate modelling, an analytical treatment of the problem and an asynchronous updating scheme that balances design space exploration and objective exploitation. Secondly, the method treats the problem as a multi-objective problem, which leads to a Pareto front of robust and reliable designs. The result is a novel series of UAV designs that are inherently free of tip stall, perform robustly and meet the stability requirements with the target reliability obtained with a computationally feasible budget. Citation: International Journal of Micro Air Vehicles PubDate: 2022-05-11T07:36:58Z DOI: 10.1177/17568293221092139 Issue No:Vol. 14 (2022)
Authors:Xice Xu, Yang Lu, Xufeng Wu Abstract: International Journal of Micro Air Vehicles, Volume 14, Issue , January-December 2022. In this paper, the design of control law for a new concept fuel-electric hybrid multi-rotor UAV with lift/attitude control separation is investigated. The remarkable feature of the UAV is that it has a large proportion of fuel weight. Firstly, based on the quasi-coordinate Lagrangian equation and sloshing equivalent model using the multi-mass-spring analogy, the non-linear dynamic model of the UAV considering the fuel slosh dynamics is established. Compared with the existing multi-rotor modeling method, it is more intuitive and accurate to describe the non-linear coupling process of sloshing and UAV's motion degrees of freedom. Secondly, the attitude control law is designed based on the finite-time sliding mode observer and cascaded continuous sliding mode controller to eliminate the adverse effects of fuel sloshing and mass changing, and only using the measurable angles. Furthermore, aiming at the problem of power redundancy of the altitude channel, a memoryless non-linear altitude authority assignment controller based on vertical acceleration is proposed for improving the control performance. Finally, the simulation results of the waypoint flight illustrate the feasibility and effectiveness of the proposed control strategy. Citation: International Journal of Micro Air Vehicles PubDate: 2022-02-15T05:46:23Z DOI: 10.1177/17568293221078925 Issue No:Vol. 14 (2022)
Authors:Suyash Verma, Muhammad S.U. Khalid, Arman Hemmati Abstract: International Journal of Micro Air Vehicles, Volume 14, Issue , January-December 2022. The association of lift generation and evolution of wake topology behind an oscillating foil with combined heaving and pitching motion is investigated numerically at a range of bluereduced frequency (0.16 [math] 0.48), phase offset (0[math] [math] 315[math]) and Reynolds number (1000 [math] 4000). The pitch-dominated kinematics that coincide with the range of [math] 120[math] and [math] 225[math] suggests that leading edge vortices are suppressed while trailing edge vortices dominate the wake with increasing reduced frequency. This corresponds to a transition in wake topology from a [math] to a reverse Von Kármán wake mode. Contrarily, heave dominated kinematics (120[math] [math] 225[math]) did not exhibit any wake topology transition with increasing [math]. The temporal lift variation associated with heave-dominated regime further revealed a symmetric feature in terms of the time taken to attain peak lift generation within an oscillation cycle. This temporal symmetry was, however, lost as kinematics transitioned from heave- to pitch-dominated regime. Analyzing the wake evolution and lift features at quarter phase of an oscillation cycle revealed the existence of a correspondence between the two processes during the heave- and pitch-dominated kinematics. Citation: International Journal of Micro Air Vehicles PubDate: 2022-01-24T01:04:37Z DOI: 10.1177/17568293211073959 Issue No:Vol. 14 (2022)
Authors:Pietro Li Volsi, David Gomez-Ariza, Romain Gojon, Thierry Jardin, Jean-Marc Moschetta Abstract: International Journal of Micro Air Vehicles, Volume 14, Issue , January-December 2022. The more restrictive airspace regulations force drone manufacturers to take into account the noise emitted by the drone during the design phase, along with its aerodynamic performance to increase the flight time. A Non-Linear Vortex Lattice Method (NVLM), coupled with the Farassat Formulation-1A of the Ffowcs-Williams and Hawkings acoustic analogy is used to evaluate the aerodynamic and aeroacoustic performance of MAV rotors. Pymoo, a Python-based optimization framework, is employed to modify the geometry, evaluate its performance and extract the set of Pareto optimal solutions. The two objectives are the aerodynamic Figure-of-Merit and the Sound Pressure Level of the Blade Passing Frequency tone for a microphone located at a far-field distance of 1.62 m and 30[math] below the rotor plane. The approach proposed in this paper takes into account up to ten different parameters, ranging from the twist and chord distributions, to the rake and skew angles. Citation: International Journal of Micro Air Vehicles PubDate: 2022-01-24T01:04:07Z DOI: 10.1177/17568293211070827 Issue No:Vol. 14 (2022)
Authors:Shushuai Li, Christophe De Wagter, Guido C. H. E. de Croon Abstract: International Journal of Micro Air Vehicles, Volume 14, Issue , January-December 2022. Wireless ranging measurements have been proposed for enabling multiple Micro Air Vehicles (MAVs) to localize with respect to each other. However, the high-dimensional relative states are weakly observable due to the scalar distance measurement. Hence, the MAVs have degraded relative localization and control performance under unobservable conditions as can be deduced by the Lie derivatives. This paper presents a nonlinear model predictive control (NMPC) by maximizing the determinant of the observability matrix to generate optimal control inputs, which also satisfy constraints including multi-robot tasks, input limitation, and state bounds. Simulation results validate the localization and control efficacy of the proposed MPC method for range-based multi-MAV systems with weak observability, which has faster convergence time and more accurate localization compared to previously proposed random motions. A real-world experiment on two Crazyflies indicates the optimal states and control behaviours generated by the proposed NMPC. Citation: International Journal of Micro Air Vehicles PubDate: 2022-01-21T12:41:33Z DOI: 10.1177/17568293211073680 Issue No:Vol. 14 (2022)
Authors:H.J. Karssies, C. De Wagter Abstract: International Journal of Micro Air Vehicles, Volume 14, Issue , January-December 2022. Hybrid UAVs have gained a lot of interest for their combined vertical take-off & landing (VTOL) and efficient forward flight capabilities. But their control is facing challenges in over-actuation and conflicting requirements depending on the flight phase which can easily lead to actuator saturation. Incremental Non-linear Control Allocation (INCA) has been proposed to solve the platform’s control allocation problem in the case of saturation or over-actuation by minimizing a set of objective functions. This work demonstrates INCA on quadplanes, an in-plane combination between a quadrotor and a conventional fixed-wing, and proposes an extension to control the outer loop. The novel controller is called Extended INCA (XINCA) and adds the wing orientation as a force-generating actuator in the outerloop control optimization. This leads to a single controller for all flight phases that avoids placing the wing at negative angles of attack and minimizes the load on hover motors. XINCA has low dependence on accurate vehicle models and requires only several optimization parameters. Flight simulations and experimental flights are performed to demonstrate the performance. Citation: International Journal of Micro Air Vehicles PubDate: 2022-01-21T12:41:14Z DOI: 10.1177/17568293211070825 Issue No:Vol. 14 (2022)
Authors:Pengfei Yu, KC Wong Abstract: International Journal of Micro Air Vehicles, Volume 14, Issue , January-December 2022. This paper presents an implementation framework to perform a vision-guided, bat-like inverted perching maneuver with a bi-directional thrust quadrotor platform. The framework consists of several distinct modules (guidance, motion planning, control, state estimation) that can be easily be individually customized in the future to meet specific research requirements. The main contribution of this paper lies in the whole framework pipeline with a modular structure developed for implementing a generalized framework for an agile quadrotor to achieve inverted perching. A computationally-light guidance module has been developed as an example to demonstrate the capability while being independent of accurate pre-known target information, and does not require the state estimation of the quadrotor to be provided by an external motion capture system as in our previous work. A motion planning module based on an optimization method has been introduced to generate a two-stage inverted perching trajectory aiming at minimizing altitude loss during the half-flip maneuver. A control module has been developed to enable a bi-directional quadrotor to fly in both upright and inverted states and closely follow the intended trajectory. The compensation strategy used in the control module is key to minimizing the transition time between the upright and inverted states. Finally, an experimental flight platform has been developed to demonstrate the capabilities of the framework. During testing, the proposed framework has achieved an 80 % success rate. To the best of our knowledge, this paper presents the first time a quadrotor has achieved the inverted perching maneuver using onboard vision guidance. Citation: International Journal of Micro Air Vehicles PubDate: 2022-01-18T11:56:06Z DOI: 10.1177/17568293211073672 Issue No:Vol. 14 (2022)
Authors:Gautier Hattenberger, Murat Bronz, Jean-Philippe Condomines Abstract: International Journal of Micro Air Vehicles, Volume 14, Issue , January-December 2022. The aim of this work is to estimate the average wind influencing a quadrotor drone only based on standard navigation sensors and equations of motion. It can be used in several situation, including atmospheric studies, trajectory planning under environmental constraints, or as a reference for studying flights in shear layer. For this purpose, a small quadrotor drone with spherical shape has been developed. Flight data are recorded from telemetry during indoor and outdoor flight tests and are post-processed. The proposed solution is based on a calibration procedure with global optimization to extract the drag model and a Kalman Filter for online estimation of the wind speed and direction. Finally, an on-board implementation of the real-time estimation is demonstrated with real flights in controlled indoor environment. Citation: International Journal of Micro Air Vehicles PubDate: 2022-01-13T01:05:53Z DOI: 10.1177/17568293211070824 Issue No:Vol. 14 (2022)
Authors:Gautier Hattenberger, Titouan Verdu, Nicolas Maury, Pierre Narvor, Fleur Couvreux, Murat Bronz, Simon Lacroix, Grègoire Cayez, Gregory C. Roberts Abstract: International Journal of Micro Air Vehicles, Volume 14, Issue , January-December 2022. Drones are commonly used for civil applications and are accessible to those with limited piloting skills in several scenarios. However, the deployment of a fleet in the context of scientific research can lead to complex situations that require an important preparation in terms of logistics, permission to fly from authorities, and coordination during the flights. This paper is a field report of the flight campaign held at the Barbados Island as part of the NEPHELAE project. The main objectives were to fly into trade wind cumulus clouds to understand the microphysical processes involved in their evolution, as well as to provide a proof of concept of sensor-based adaptive navigation patterns to optimize the data collection. After introducing the flight strategy and context of operation, the main challenges and the solutions to address them will be presented, to conclude with the evaluation of some technical evolution developed from these experiments. Citation: International Journal of Micro Air Vehicles PubDate: 2022-01-10T01:30:02Z DOI: 10.1177/17568293211070830 Issue No:Vol. 14 (2022)
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