Solar Unmanned Aerial Vehicle Research Articles

Overview and Energy Power Analysis of Composite Solar Unmanned Aerial Vehicles

In this paper, based on the existing research progress and challenges in unmanned aerial vehicles (UAVs), efforts are made to enhance the performance of UAVs in terms of endurance and range by optimizing the energy and power systems. We propose the concept of a composite UAV and further introduce the concept of a solar-powered UAV. The paper outlines the project's design philosophy and innovative aspects, followed by an exploration of potential applications. Energy control calculations are then conducted, leading to the proposal of a gravity energy storage strategy. Then a preliminary flight control scheme is presented. This paper concludes with a conclusion and prospects for future work.

Experimental Study to Increase the Autonomy of a UAV by Incorporating Solar Cells

Solar energy is recognized as an alternative to combustion engines to reduce the environmental impact and increase the endurance of unmanned aerial vehicles (UAVs). This work aims to present a project for a solar UAV to contribute to the mission of the Air Force Academy Research Center and test the energy system on the ground. To achieve this study’s objectives, a literature review on photovoltaic cells (PVCs), batteries, and maximum power point tracking algorithms was conducted. The most appropriate airframe and wing designs for this particular type of flight are then investigated. Following that, the project requirements and mission profile were defined, and the copper indium gallium selenide eFilm cells, a solar power management system (SPMS), avionics, and payload required for the mission were chosen based on them. A methodology for ground testing of solar systems was created and used, achieving an endurance of 7 h and 34 min on an April day. The SPMS achieved an efficiency of around 96%, while PVCs ranged from 11.3 to 14.1%.

Aerodynamic Investigation and Simulation Studies on Wing Section of an Unmanned Aerial Vehicle Attached with Solar Plate

The paper investigates the aerodynamic performance and power requirement characteristics of wing sections integrated with high-lift airfoil to support the operation of solar-powered Unmanned Aerial vehicle (UAV). The flight mission is aimed to simulate the operation of solar-powered UAVs under low -speed environment. The research focuses on studying the aerodynamic effect of non-solar UAV wing model and solar UAV wing model for the varying angle of attack. The UAV wing models are tested using a subsonic wind tunnel to validate the aerodynamic characteristics at low-speed condition. The aerodynamic parameters such as coefficient of lift (Cl), coefficient of drag (Cd), coefficient of pressure (Cp), and the total power required to accelerate the solar UAV are studied to maintain steady level flight. The solar UAV and non-solar UAV wing models were subjected to a computational process to examine the pressure and velocity distributions for the aerodynamic performance analysis. Evident results show that the solar cells positioned at the flow separation region of the UAV wing model produces an aerodynamic efficiency rate of 5.45% and required 37.13W of minimum power compared to non-solar UAV at the Reynolds number of 9.8 106.

Design of Solar Endurance Control for Unmanned Aerial Vehicles based on Schmidt Trigger Control

In order to improve the endurance of unmanned aerial vehicles (UAVs), a power supply controller with automatic switching between solar energy and battery was designed. The controller is mainly composed of an AT89C51 single chip microcomputer. By collecting ambient light intensity and comparing it with the preset light intensity of the system, the controller completes automatic switching of the power supply for solar unmanned aerial vehicles, thereby achieving continuous and stable power supply for solar unmanned aerial vehicles. In addition, the implementation method of the single-chip microcomputer program in the controller is also introduced. The control core is to use Schmidt de shake control to switch between solar energy and battery, and to test the various functions of the controller through the flight experiment of a small solar powered unmanned aerial vehicle. Tests have found that solar powered drones using this controller can navigate for a long time in weather with varying light intensity, and the device operates well, effectively improving the power stability of solar powered drones.

Research on route planning for solar UAV based on the intelligent optimization algorithm.

The solar unmanned aerial vehicle (UAV) route planning needs to comprehensively consider the conversion efficiency of solar cells under the influence of solar ground reflection radiation and sky scattering radiation. On the one hand, it is necessary to consider the cost of radar threat, mileage energy consumption, mountain impact and other costs. On the other hand, it is also necessary to consider the influence of high threat, mountain shadow occlusion cost, and cloud shading cost on solar photovoltaic conversion efficiency. The above problem was solved through using the ant colony intelligent optimization algorithm. By constructing ant colony paths rationally, models of mountain impact cost, high threat, mountain shadow shelter cost, and cloud shading cost were established. The constraints such as the maximum action distance, solar irradiation angle and effective action distance of various costs were introduced into the cost model and exploration factor calculation, and the comprehensive optimization problem of solar UAV route was solved. Finally, the simulation results show that the algorithm path structure is reasonable; the target node can be found independently; the convergence speed can meet the requirements of route planning; the generated route cost is small; the algorithm is reasonable and effective.

Optimal trajectory planning of a small UAV using solar energy and wind energy

Due to size limitations and the working environment near the ground, small low-altitude unmanned aerial vehicles (UAVs) cannot carry large-area solar cells and energy storage devices. Solar energy alone has only a limited effect on the improvement of their endurance. To solve this problem, this study proposes the combination of solar energy technology and dynamic soaring technology to improve the endurance of small UAVs. Then, the optimal energy acquisition strategy based on the combination of solar energy and dynamic soaring technology is analyzed in terms of energy. The motion equations and energy acquisition and consumption models of a small solar UAV based on horizontal wind shear are established. Moreover, an optimal trajectory planning problem with the maximum charging power of rechargeable batteries as the optimization objective is proposed. The optimal trajectory is solved based on the hp adaptive pseudo-spectral method, and the optimal trajectory combining the two technologies is simulated and compared with the constant-altitude constant-velocity (CACV) trajectory of the UAV using only solar technology. The simulation results show that under the flight background of tmission = 6:00 (summer sunrise) and β = 0.125 s−1 (wind gradient of the wind shear), the optimized O-type trajectory decreased the energy consumption power by 39.86% and increased the solar energy acquisition power by 86.34% compared to the CACV trajectory. Consequently, the small UAV stores more energy in the rechargeable batteries to improve the endurance performance. Compared to the environment where the sun is located on the leeward side of the wind shear, the environment where the sun is located on the windward side of the wind shear can enable the UAV to acquire more energy through the optimized O-type trajectory.

Solar UAVs—More Aerodynamic Efficiency or More Electrical Power?

Solar UAVs (unmanned aerial vehicles) have experienced important development in recent years. The use of solar free energy is not neglected in the present energy crisis, with the intention to move toward green energies. However, an important problem arises concerning the limited amount of solar energy available on board UAVs. Until now, high-aerodynamic-efficiency configurations have been used. These configurations use high-aspect-ratio wings. However, high-aspect-ratio wings have some disadvantages regarding their excessive elasticity and weak bending resistance in the housing section. Additionally, the aircraft maneuverability is reduced. In this work, a study is proposed on a solar UAV configuration that sacrifices high aerodynamic efficiency for a higher surface area available for solar cells. In this manner, the amount of energy available on board the UAV is increased, and the UAV structure becomes more rigid and robust. The presented UAV fits better with more complex evolutions, is more maneuverable and the wingspan is much reduced. This UAV is more compact, can maneuver better in the take-off and landing phases, and the necessary storage space is considerably reduced. This paper highlights the performances that can be achieved using this kind of UAV and explores whether these performances are enough for some applications. Using an on-board energy balance, the possible performances of this new configuration is studied. As this is a preliminary study, the precision level is not very high, but it offers an image concerning the possibilities of this new configuration.

Design of longitudinal autopilot for Sky Sailor UAV using SLC and TECS controllers

in recent years, UAVs (Unmanned Aerial Vehicle) have become playing an active role and have been involved in a number of fields such as surveillance, photography, agriculture, transportation and communications. For this reason, the research institution is working to develop linear and non-linear controllers to make these UAVs more stable and effective while performing various tasks assigned to them. In this paper, a longitudinal autopilot was designed for a solar UAV (sky sailor) using two controllers, the first is SLC (Successive Loop Closure) which is a classic controller that is based on successive loops with a PID controller, and the second method is the TECS (Total Energy Control System) controller that depends on the total specific energy rate and the energy distribution rate to control the airspeed and altitude of the UAV. After detailing the working principle and tuning of each controller they were applied to the non-linear model of UAV using MATLAB Simulink. Through the results obtained from the simulations, we conclude that the TECS controller is better than the SLC controller in terms of stability and energy economy, being an ideal choice for solar UAVs to increase their endurance, and for civil aircraft to reduce the cost of flights.

MDAO and Aeroelastic Analyses of Small Solar-Powered UAVs with Box-Wing and Tandem-Wing Architectures

The market of solar-powered Unmanned Aerial Vehicles (UAVs) for defence purposes and drone services is expected to grow by a factor of more than 2 in the next decade. From an aircraft design perspective, the main challenge is the scalability of the proposed architectures, which is needed to increase the payload capabilities. Beside some successful examples of wing-tail UAVs, some newcomers are developing prototypes with tandem-wing architectures, hence enlarging the possible design. The present paper aims to introduce a further step in this direction, taking also the box-wing architecture into account to show how the presence of wing tip joiners can provide benefits from the aeroelastic point of view. UAVs with take-off mass within 25 kg are considered and the main tools adopted are presented. These are an in-house developed Multi-Disciplinary Analysis and Optimization (MDAO) code called SD2020 and the open source aeroelastic code ASWING, both presented together with an assessment of their accuracy by means of higher fidelity numerical results. SD2020 results are presented for the case of small box-wing solar UAVs optimized to achieve the longest endurance, focusing on the strategy implemented to achieve feasible solutions under an assigned set of constraints. Further results are presented for comparable box-wing and tandem-wing UAVs from both the aerodynamic and aeroelastic standpoints. Whereas the aerodynamic advantages introduced by the box-wing are marginal, significant advantages result from the aeroelastic analyses which indicate that, if the joiners are removed from the box-wing configuration, safety margin from flutter speed is halved and the bending-torsion divergence occurs at relatively low speed values.

Ponder: Enabling Balloon-Borne Based Solar Unmanned Aerial Vehicle's Take Off Diagnosis under Little Data.

Balloon-borne based solar unmanned aerial vehicle (short for BS-UAV) has been researched prevalently due to the promising application area of near-space (i.e., 20–100 km above the ground) and the advantages of taking off. However, BS-UAV encounters serious fault in its taking off phase. The fault in taking off hinders the development of BS-UAV and causes great loss to human property. Thus, timely diagnosing the running state of BS-UAV in taking off phase is of great importance. Unfortunately, due to lack of fault data in the taking off phase, timely diagnosing the running state becomes a key challenge. In this paper, we propose Ponder to diagnose the running state of BS-UAV in the taking off phase. The key idea of Ponder is to take full advantage of existing data and complement fault data first and then diagnose current states. First, we compress existing data into a low-dimensional space. Then, we cluster the low-dimensional data into normal and outlier clusters. Third, we generate fault data with different aggression at different clusters. Finally, we diagnose fault state for each sampling at the taking off phase. With three datasets collected on real-world flying at different times, we show that Ponder outperforms existing diagnosing methods. In addition, we demonstrate Ponder’s effectiveness over time. We also show the comparable overhead.

Improvements on permanent magnet synchronous motor by integrating heat pipes into windings for solar unmanned aerial vehicle

The successful market uptake of all-electric propulsion systems is closely related to the performance metrics of the electrical motor used within. In light of this, various road-maps have been set for the next two decades by aerospace and automotive bodies targeting ambitious future targets of the motor's power densities and efficiencies. In achieving motors with such step-improvement performance metrics, often the thermal management is a key challenge. In this paper, a cooling structure for a propulsion motor of solar unmanned aircraft is proposed which combines the stator windings with heat pipes, and which is shown to simultaneously improve the heat dissipation as well as the efficiency. This paper firstly determines the heat transfer characteristic of the heat pipe experimentally which is then used in the development of a bespoke thermal network model of the motor. The effects of the cooling structure on the motor's temperature rise, copper losses, torque, and efficiency are studied in detail. Finally, a prototype is developed and a test platform is built. The experimental results are consistent with the analytical result, verifying the correctness of the thermal network model and the benefits of the proposed mechanism. Compared to the motor without heat pipes, the temperature rise of the motor is reduced by 35%, while its efficiency is improved by a significant 1.5%.

An Extended Methodology for Sizing Solar Unmanned Aerial Vehicles: Theory and Development of a Python Framework for Design Assist.

There is a growing interest in using unmanned aerial vehicles (UAVs) in the most diverse application areas from agriculture to remote sensing, that determine the need to project and define mission profiles of the UAVs. In addition, solar photovoltaic energy increases the flight autonomy of this type of aircraft, forming the term Solar UAV. This study proposes an extended methodology for sizing Solar UAVs that take off from a runway. This methodology considers mission parameters such as operating location, altitude, flight speed, flight endurance, and payload to sizing the aircraft parameters, such as wingspan, area of embedded solar cells panels, runway length required for takeoff and landing, battery weight, and the total weight of the aircraft. Using the Python language, we developed a framework to apply the proposed methodology and assist in designing a Solar UAV. With this framework, it was possible to perform a sensitivity analysis of design parameters and constraints. Finally, we performed a simulation of a mission, checking the output parameters.

Acid Aging of CFRP Composite Materials for Solar UAV Structure

The purpose of this investigation is to study the performance degradation mechanism of CRRP composite materials used in the structure of a solar UAV under acid rain environment and to provide references for the structural design of the solar UAV. An aging test was designed according to the actual working conditions of the solar unmanned aerial vehicle and was carried out by continuously immersing the composite material in both deionized water and an acidic solution with a pH of 2.0 at 60°C. The mechanical behavior of the composites was studied through a three-point bending test. The results showed that after 120 days of aging test, the composite material exhibits different characteristics in the two conditions. The composite material under the hygrothermal conditions finally reached the equilibrium moisture absorption content of 1.07%, and the flexural strength decreased by 8.77%. The composite material under acidic conditions deviated from the Fick behavior in the final stage of the test, and the final moisture content was 2.88%, and the bending strength decreased by 26.43%. Several typical empirical models were analyzed, and a hyperbolic tangent function empirical model with moisture content as the main variable was used to predict the CFRP flexural strength degradation process, and good results were obtained. The effect of aging conditions on the microstructure of composite materials was observed by SEM, and the aging mechanism of composite materials was analyzed. The corrosion of the polymer matrix and the debonding of the fiber/matrix interface are the root causes of the performance degradation of composite materials.

Design and Implementation of an Innovative Series Power Supplies for Solar Unmanned Aerial Vehicles

Conventional unmanned aerial vehicles power systems only have one MPPT controller to operate. And MPPT controller will be influenced by loss of solar arrays and multiple maximum power points. In this paper, an innovative topology of UAV power system is proposed as well as generating a related MPPT control strategy to keep output voltage increase slowly. Hardware circuit design is presented based on selection of power diode, input filter capacitance, output filter capacitance and parallel diode. A prototype of 1.2kW power supplies is implemented to verify the proposed topology and MPPT control strategies.

Experimental Analysis of Small Solar Unmanned Aerial Vehicle to Predict Aerodynamic Performance

Various studies have been done in recent years on unmanned solar-powered aircraft for non-stop flight at a specified location or area. However, if a solar-powered unmanned aerial vehicle (UAV) can achieve a non-stop flight around the world, it may lead to the possibility of a pseudolite (i.e., pseudo-satellite) operation. These solar UAVs capable of operating as a satellite enable sustainable aviation that provides cheaper communication accessibility. Recently, we have developed a mathematical model for solar UAVs that was followed by the fabrication of a solar UAV model. Both the mathematical design model and the prototype model have been published. Thus, this work aims to determine the actual flight performance characteristics of the fabricated solar UAV. In this work, the bench and flight tests of the prototype solar and non-solar UAV model were compared in terms of aerodynamic characteristics and performance. These characteristics are determined using the flight test data and then compared with simulation data using a mathematical design model published earlier. Both accelerated and un-accelerated methods have been applied to predict the polar drag curve, and a distinct band of data obtained for both UAV prototypes. The predicted zero-lift drag coefficients were similar to the theoretical prediction in these UAVs.

Optimal Energy Utilization for a Solar-Powered Aircraft using Sliding Mode-Based Attitude Control

In this article, an energy optimal dynamic attitude for a solar-powered aircraft is determined and implemented using the finite-time sliding-mode approach. A nonlinear constrained optimization technique has been considered to determine the optimal attitude of the aircraft for given a geographical location, solar position, heading direction, and other flight conditions for clear sky conditions. The optimization is performed so as to travel in the fastest possible way from one location to another location without utilizing the battery power, provided the solar energy is sufficient for the flight. The gain in the velocity due to the attitude optimization is validated with the test flight results of solar unmanned aerial vehicle (UAV) Maraal, which demonstrate the efficacy of the approach proposed here. Computational fluid dynamics (CFD) simulation is carried out to estimate aerodynamic forces acting on the aircraft at different sideslip angles. The developed aircraft dynamics incorporates the nonlinearities associated with relatively large aileron and rudder deflections. To obtain the desired attitude, a sliding-mode-based control scheme is considered. A power rate reaching law is applied to avoid chattering in the controls. Finite-time stability of the closed-loop system is discussed and it is shown that the attitude angles reach the desired values in finite time.

Design and Optimization of a High-altitude Long Endurance UAV Propeller

This paper presents a propeller designed for a solar unmanned aerial vehicle (UAV) at 22km altitude. The design objective for the 3-blade propeller is to achieve 72% efficiency and 7 N thrust, with 0.5588m diameter propeller rotating at 5500rpm under freestream velocity 50m/s. For such High-Altitude Long Endurance (HALE) flight vehicle, firstly, three low Reynolds number airfoils were assessed by airfoil aerodynamic performance analysis software Profili. As a result, FX 63-137 was selected for the best lift to drag ratio at given altitude. Secondly, a MATLAB program based on Joukowski propeller vortex theory was employed to determine three dimensional configuration of the blades. Then, CFD simulation was carried out on the preliminary design. Furthermore, optimal design method was employed to improve propeller efficiency of the preliminary design using software ISIGHT. Ten variables including chord lengths and blade pitch angles distribution at five spanwise sections were employed. Finally, the optimized propeller with power 467W was obtained, performance satisfying the requirement.

Energy acquisition of a small solar UAV using dynamic soaring

ABSTRACTDynamic soaring improves the endurance of Unmanned Aerial Vehicles (UAVs) by obtaining energy from the horizontal wind shear gradient. The use of dynamic soaring in small solar UAVs can mitigate the trade-off between energy capacity and battery weight to achieve continuous all-day flight. The goal of this study is to determine the optimal energy acquisition methods for small solar UAVs using dynamic soaring and to decrease the battery weight to achieve all-day flight. A dynamic soaring UAV model that considers the influence of the wind shear gradient and a solar power energy model are established. The conditions to obtain a closed-loop energy system during daytime and nighttime flights are discussed, and the minimum mass of the energy system required for these conditions is determined. Simulations of single-cycle circular flights and a 72-h continuous flight of a small solar UAV are performed. The analyses and simulation results show that: (1) the combination of dynamic soaring and solar technology significantly reduces the energy consumption and reduces the required battery weight, (2) the flight speed and flight attitude angles have significant effects on the optimal total energy acquisition and (3) wind fields with a large horizontal gradient and strong solar illumination provide energy and load advantages.

Aerodynamics, Stability and Control Analysis of Tactical Solar Power UAV

This paper addresses the fundamental aerodynamics, stability, and control analysis of a solar power Unmanned Aerial Vehicle (UAV) as a part of the preliminary design stage. The tactical solar-powered UAV addressed in this paper is primarily developed for intelligence, surveillance, and reconnaissance (ISR) missions at low altitude. Moreover, such design also has a dual-use capability, which could be utilized in both military and civilian domains. The aerodynamic characteristics of the UAV are obtained from both computational fluid dynamics analysis technique and the wind-tunnel testing at the design operating Reynolds number ranging from 1x105 – 4.5x105. The fundamental aerodynamics coefficient consists of lift, drag, and pitching moment variations versus the angle of attack. The stability and control analysis was carried out based on the small disturbance theory in correlation with the XFLR5 software. The results show that the tactical solar power UAV design could achieve high aerodynamic efficiency at a 4-degree angle of attack which is corresponding to the lift-to-drag ratio of 20.05. Also, the analysis results confirm that the design possesses positive static and dynamic stability at the design cruise flight condition.

Development and Verification of Hybrid Power Controller Using Indoor HIL Test for the Solar UAV

A hybrid power system (HPS) is developed for the photovoltaic (PV) powered and tethered multirotor unmanned aerial vehicle (UAV) based on the robot operating system (ROS) and verified using an indoor hardware-in-the-loop (HIL) test. All the processes, including a UAV flight mode change (i.e., takeoff, hovering, and landing) and power flow control (consisting of PV modules, a LiPo battery pack, and a UAV) are completely automated using a combination of Pixhawk 2.1 and the Raspberry Pi 3 Model B (RPi 3B). Once the indoor HIL test starts, (1) the UAV takes off and hovers with a preassigned 10 m altitude at a fixed point and keeps hovering until the voltage drops below 13.4 V ; (2) the UAV lands when the voltage drops below 13.4 V, and the hybrid power controller (HPC) starts to charge the LiPo battery pack using the energy from PV modules; and (3) the UAV takes off when the voltage of the battery pack becomes more than 16.8 V, and the procedure repeats from (1). A PV-powered and tethered multirotor UAV using the proposed HPS can fly more safely for a longer time, particularly in an urban area, and so it is competitive to the traditional multirotor type UAV in the sense of both the flight time and the surveillance mission performance.