Authors:Yeong-Ki Jung, Kyoungsik Chang, Sang-Hwan Park, Van Thanh Ho, Ho-Joon Shim, Min-Woo Kim Pages: 1 - 12 Abstract: Unmanned Systems, Ahead of Print. In this work, 22 off-the-shelf propellers of 15–40 inches in diameter are reverse-engineered using a scanning system and reverse engineering software. Geometric information, including the diameter and pitch of the propeller and its airfoil sections, are extracted, and the chord length and twist angle of the extracted airfoil sections are investigated. All processes for reverse engineering are validated through comparison with design drawing information, product and performance data of the KPROP propeller designed by Korea Aerospace Research Institute. Based on the validated process, a database of 22 commercial propellers from four companies is constructed containing all the reverse-engineered information. The chord length, the maximum length and twist angle with respect to the diameter of the extracted airfoil section are analyzed in comparison with each other depending on the company and propeller size. In addition, the thrust and torque are simulated using computational fluid dynamic methodology, and the predictions are compared with reference data provided by the manufacturers. Citation: Unmanned Systems PubDate: 2021-01-18T08:00:00Z DOI: 10.1142/S2301385021500163
Authors:Seng Man Wong, Hann Woei Ho, Mohd Zulkifly Abdullah Pages: 45 - 63 Abstract: Unmanned Systems, Volume 09, Issue 01, Page 45-63, January 2021. The interest in building hybrid Unmanned Aerial Vehicles (UAVs) is increasing intensively due to its capability to perform Vertical Take-Off and Landing (VTOL), in addition to forward flight. With this capability, the hybrid UAVs are highly on demand in various industries. In this paper, a fixed-wing VTOL UAV with a novel configuration of a dual rotor-embedded wing was designed and developed. The methodology used in the design process adopted the traditional sizing and aerodynamic estimation method with advanced computational simulations and estimation approaches. The design was determined based on a thorough analysis of weight contribution, aerodynamics, propulsion, and stability and control. The results show that the UAV’s preliminary design has successfully reached a total weight of 1.318 kg, achieved a high lift-to-drag ratio of approximately 4, and ensured stable flights with Level 1 flying qualities. A fixed-wing VTOL prototype was developed and fabricated based on the final design parameters using a low-cost hand lay-up process. Citation: Unmanned Systems PubDate: 2020-10-02T07:00:00Z DOI: 10.1142/S2301385021500096 Issue No:Vol. 09, No. 01 (2020)
Authors:Mostafa E. El-Salamony, Mohamed A. Aziz Pages: 1 - 12 Abstract: Unmanned Systems, Ahead of Print. Generally, unmanned aerial vehicles and micro aerial vehicles depend on batteries or conventional fuel as a source of energy. These sources of energy have limited flight time, relatively high cost, and also a certain level of pollutants. Solar energy applied to aerial vehicles is an excellent alternative way to overcome other sources of energy’s disadvantage. This study aimed to design a solar-powered aerial vehicle to achieve continuous flight on Earth. The efficiency of the solar system is related to the absorbed sun rays. The concept of an anti-symmetric N-shaped morphing wing is a good idea to increase the collected solar energy during the daily sun path. But this comes with the penalty of side forces and moments due to the anti-symmetry of the wing. This paper introduces a study for two parameters that strongly affect the aerodynamics of the N-shaped morphing wing; the dihedral part angle and the dihedral part length. The impact of the dihedral angle decreases the lift coefficient and increases the drag coefficient. The impact of the morphing wing on the aircraft performance is also considered. Citation: Unmanned Systems PubDate: 2020-12-21T08:00:00Z DOI: 10.1142/S2301385021500138
Authors:Yu Herng Tan, Ben M. Chen Pages: 1 - 20 Abstract: Unmanned Systems, Ahead of Print. As the development of mobile robots matures, there is an increasing amount of interest in expanding the functionality of such robots through developing multimodal locomotion. As compared to land–water or land–air hybrids, the design of air–water vehicles is much less straightforward due to the fact that both mediums are three-dimensional fluid spaces and there is inherent disparity in fluid properties between them. As such, the development of these vehicles has received limited attention until very recently. Nevertheless, the potential applications of such vehicles range widely from military surveillance, oceanic data collection to heterogeneous robot team operation, which has led to an increasing number of projects working on aerial–aquatic hybrid mobility. In this paper, we discuss the fundamental challenges associated with aerial–aquatic hybrid locomotion as well as the necessary trade-offs in design decisions. We also summarize and review the existing work and prototypes of aerial–aquatic vehicles that have been designed thus far, analyzing the range of solutions that have been adopted to solve the aforementioned challenges. Lastly, the limitations of these solutions are analyzed to offer a perspective on how future developments in the area can enable greater functionality for the concept. Citation: Unmanned Systems PubDate: 2020-12-10T08:00:00Z DOI: 10.1142/S2301385021410028
Authors:A. Hamissi, K. Busawon, L. Dala, Y. Bouzid, M. Zaouche, M. Hamerlain Pages: 1 - 16 Abstract: Unmanned Systems, Ahead of Print. This paper proposes a novel nonlinear feedback control strategy for velocity and attitude control of fixed wing aircrafts. The key feature of the control design strategy is the introduction of a virtual control input in order to deal with the underactuation property of such vehicles and to indirectly control the orientation of the aircraft. As such, the proposed strategy consists of three control loops each realizing a specific task. Simulations are carried out by using the jetstream-3102 aircraft in a real-time virtual Simulation Platform for the development of Aircraft Control Systems (SP-ACS). The proposed approach of control is model-based for which we have introduces an identification part before test and validation. We use the Total Least Squares Estimation (TLSE) technique to identify the aerodynamic parameters, which are unknown, variable and classified. Each aerodynamic coefficient is defined as the mean of its numerical values. All other variations are considered as modeling uncertainties that will be compensated by the robustness of the piloting law. Simulation results on Jetstream-3102 aircraft show very good performance in terms of convergence towards the desired reference trajectories and in terms of robustness with respect to modeling uncertainties. Citation: Unmanned Systems PubDate: 2020-11-25T08:00:00Z DOI: 10.1142/S2301385021500126
Authors:Han Fu, Hugh H.-T. Liu Pages: 1 - 16 Abstract: Unmanned Systems, Ahead of Print. A target defense game with two defenders and a faster intruder is solved based on the classic differential game theory. In the game, the intruder seeks to enter a circular target area, while the defenders endeavor to capture it outside of the target. Under the faster intruder assumption, the game has two phases, where the optimal trajectories are straight and curved, respectively. In the second phase, a peculiar phenomenon exists where the intruder moves at the edge of one defender’s capture region, yet this defender cannot force capture. Because of this, the terminal states of the game are singular, therefore the standard method of integrating optimal trajectories from terminal states is not applicable. The way to circumvent this singularity is to solve the optimal trajectories of a two-player game between the intruder and the closer defender, and assemble them with the trajectory of the other defender. The key contribution of this paper is the solution of the intruder-closer-defender subgame against a circular target area. In the vector field of the optimal trajectories, two singular surfaces and a singular point are observed. Each singular surface indicates a discontinuity in the closer defender’s control, while the singular point represents a situation where the target is successfully protected by a single defender. The complete solution of the two-defender game is solved based on the result of the intruder-closer-defender subgame. The proposed solution is verified through a special case where the capture range is zero. This verification also presents a simpler approach of solving the zero capture range problem. Citation: Unmanned Systems PubDate: 2020-10-30T07:00:00Z DOI: 10.1142/S2301385021410016
Authors:Simone A. Ludwig Pages: 1 - 9 Abstract: Unmanned Systems, Ahead of Print. Inertial Measurement Units (IMUs) were first applied to aircraft navigation and large devices in the 1930s. At that time their application was restricted because of constraints such as size, cost, and power consumption. In recent years, however, Micro-electromechanical (MEMS) IMUs were introduced with very favorable features such as low cost, compactness, and low processing power. One of the disadvantages of these low cost IMU sensors is that the accuracy is lower compared to high-end sensors. However, past experimental results have shown that redundant Magnetic and Inertial Measurement Units (MIMUs) improve navigation performance such as for unmanned air vehicles. Even though past simulation and experimental results demonstrated that redundant sensors improve the navigation performance, however, none of the current research work offers information as to how many sensors are required in order to meet a certain accuracy. This paper evaluates different numbers of sensor configurations of an MIMU sensor array using a simulation environment. Differently rotated MIMU sensors are incrementally added and the Madgwick filter is used to estimate the Euler angles of foot mounted MIMU data. The evaluation measure used is the root mean square error (RMSE) based on the Euler angles as compared to the ground truth. During the experiments it was noticed that the execution time with increasing number of sensors increases exponentially, and thus, the parallelization of the code was designed and implemented, and run on a multi-core machine. Thus, the speedup of the parallel implementation was evaluated. The findings using the parallel version with 16 sensors are that the execution time is less than twice the execution time of having only 1 sensor and 24 times less than using the sequential version with the added benefit of a 26% increase in accuracy. Citation: Unmanned Systems PubDate: 2020-10-29T07:00:00Z DOI: 10.1142/S2301385021500114
Authors:Nate Quirion, Dahai Liu Pages: 1 - 11 Abstract: Unmanned Systems, Ahead of Print. In recent years, Unmanned Aerial Systems (UASs) development and application have achieved remarkable growth. With the advancement of technology, UASs nowadays feature more advanced autonomous capabilities than ever before. In order to achieve autonomous behavior, intelligent systems are required to be incorporated to support system learning, control and decision-making. With these capabilities, UASs can learn from their past experiences, through interacting with the task environment to adapt their behavior to enhance their future performance. Machine learning is one of the most commonly used techniques for UASs to acquire knowledge from their experience, and research in this area is still developing. In this study, Reinforcement Learning (RL) algorithms were used on autonomous aerial systems to achieve adaptive behavior and decision-making capabilities. The effects of UAS sensor sensitivity, as modeled through Signal Detection Theory (SDT), on the ability of RL algorithms to accomplish a target localization task were investigated. Three levels of sensor sensitivity were simulated and compared to the results of the same system using a perfect sensor, with the consideration of two RL algorithms, namely, Temporal Difference (TD) and Monte Carlo (MC) methods. Target localization and identification task were used as the test bed, and a hierarchical architecture was developed with two distinct agents. Mission performance was analyzed using multiple metrics, including episodic reward and the time taken to locate all targets. Statistical analyses were carried out to detect significant differences in the comparison of steady-state behavior of different factors. Results were discussed, and future research direction was given at the end of the paper. Citation: Unmanned Systems PubDate: 2020-10-02T07:00:00Z DOI: 10.1142/S2301385021500023
Authors:Xiaofeng Chai, Jian Liu, Yao Yu, Jianxiang Xi, Changyin Sun Pages: 1 - 12 Abstract: Unmanned Systems, Ahead of Print. In this paper, we study the practical fixed-time event-triggered time-varying formation tracking problem of leader-follower multi-agent systems with multi-dimensional dynamics. Fixed-time event-triggered control schemes with continuous communication and intermittent communication are developed, respectively. Continuous communication and measurement are avoided, and computation cost is reduced greatly in the latter scheme. And the settling time is to be specified regardless of initial states of agents. Meanwhile, tracking errors are adjustable as desired with expected settling time. It is demonstrated that time-varying formation tracking can be achieved under the two proposed control schemes and Zeno behavior can be excluded. Finally, numerical examples are provided to illustrate the effectiveness of the proposed control strategies. Citation: Unmanned Systems PubDate: 2020-10-02T07:00:00Z DOI: 10.1142/S2301385021500035
Authors:Mohanad Alnuaimi, Mario G. Perhinschi Pages: 1 - 8 Abstract: Unmanned Systems, Ahead of Print. This paper is focused on analyzing effects of several significant parameters on the performance of an immunity-inspired methodology for autonomous navigation of unmanned air vehicles when measurements from global navigation satellite systems (GNSS) or similar current sources, including external information of opportunity, are not available. An artificial immune system (AIS) provides corrections to a dead reckoning algorithm for adequate estimates of vehicle position and velocity. Parameter effects are assessed and analyzed through simulation in terms of trajectory tracking errors during autonomous flight. Citation: Unmanned Systems PubDate: 2020-10-02T07:00:00Z DOI: 10.1142/S2301385021500059
Authors:Qiuyang Tao, Tun Jian Tan, Jaeseok Cha, Ye Yuan, Fumin Zhang Pages: 1 - 14 Abstract: Unmanned Systems, Ahead of Print. Swing oscillation is widely observed among indoor miniature autonomous blimps (MABs) due to their underactuated design and unique aerodynamic shape. This paper presents the modeling, identification and control system design that reduce the swing oscillation of an MAB during hovering flight. We establish a dynamic model to describe the swing motion of the MAB. The model parameters are identified from both physical measurements, computer modeling and experimental data captured during flight. A control system is designed to stabilize the swing motion with features including low latency and center-of-mass (CM) position estimation. The modeling and control methods are verified with the Georgia-Tech Miniature Autonomous Blimp (GT-MAB) during hovering flight. The experimental results show that the proposed methods can effectively reduce the swing oscillation of GT-MAB. Citation: Unmanned Systems PubDate: 2020-10-02T07:00:00Z DOI: 10.1142/S2301385021500060
Authors:M. El-Salamony, S. Serokhvostov Pages: 1 - 9 Abstract: Unmanned Systems, Ahead of Print. Geometry and mass of an aircraft are important factors in flight mechanics and in the calculations of stability and natural frequencies of its flight modes, which are of great importance in controller design process. In this paper, comparison between the formulae of the large aircraft applied on small UAVs scale, XFLR5 as a numerical program and experimental data obtained from flight tests is made to investigate their accuracy. A method to validate natural frequencies for UAVs is presented. It is found that for the phugoid mode, methods of Roskam (exact), Ostoslavsky, and XFLR5 estimate the frequency within range of the experimental results while the methods of Roskam (approximation) and Hull overestimate it and should not be applied in case of small UAVs. Considering the short-period mode, all methods can predict the actual frequency with acceptable accuracy. Citation: Unmanned Systems PubDate: 2020-07-25T07:00:00Z DOI: 10.1142/S2301385020500211
Authors:Wei Zhang, Yunfeng Zhang, Ning Liu Pages: 1 - 9 Abstract: Unmanned Systems, Ahead of Print. Self-navigation, referred as the capability of automatically reaching the goal while avoiding collisions with obstacles, is a fundamental skill required for mobile robots. Recently, deep reinforcement learning (DRL) has shown great potential in the development of robot navigation algorithms. However, it is still difficult to train the robot to learn goal-reaching and obstacle-avoidance skills simultaneously. On the other hand, although many DRL-based obstacle-avoidance algorithms are proposed, few of them are reused for more complex navigation tasks. In this paper, a novel danger-aware adaptive composition (DAAC) framework is proposed to combine two individually DRL-trained agents, obstacle-avoidance and goal-reaching, to construct a navigation agent without any redesigning and retraining. The key to this adaptive composition approach is that the value function outputted by the obstacle-avoidance agent serves as an indicator for evaluating the risk level of the current situation, which in turn determines the contribution of these two agents for the next move. Simulation and real-world testing results show that the composed Navigation network can control the robot to accomplish difficult navigation tasks, e.g. reaching a series of successive goals in an unknown and complex environment safely and quickly. Citation: Unmanned Systems PubDate: 2020-07-23T07:00:00Z DOI: 10.1142/S2301385021500011
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