High Altitude Long Endurance Unmanned Aerial Vehicle Research Articles

Unsteady aerodynamic interaction in regulated two-stage radial turbine at pulsating conditions

Regulated multi-stage turbocharging is an indispensable technology to achieve high boosting pressure and hence power recovery for High-Altitude Long-Endurance Unmanned Aerial Vehicle (HALE UAV). Inevitably, unsteady interstage coupling has become a key factor restricting the pursuit of higher aerodynamic performance in multi-stage turbochargers. This study is to investigate the unsteady gasdynamic behavior of two-stage radial turbines and aimed to obtained the knowledge of unsteady aerodynamic interaction at pulsating conditions. Results reveal an obvious difference in the performance discrepancy mechanisms of high-pressure turbine (HPT) and low-pressure turbine (LPT). HPT shows more unsteady than that of LPT according to the discussion on mass accumulation and local temporal gradient. Furthermore, this unsteadiness is drastically enhanced when the valve is open. For HPT with open valve, a sharp reduction of up to 10.7% in the cycle-averaged efficiency is observed. Both the volute and the rotor are the main components causing the deterioration of efficiency. Swirling flow precession leads to a dramatically loss generation in the volute. Leading-edge separation and tip leakage flow are the dominated factors in rotor. The former is primarily attributed to inlet swirling flow and the latter is predominantly attributed to the pulsating effect. For LPT, the performance is not sensitive to the valve state, with no more than 3% discrepancy on efficiency. At specific velocity ratio, the negative swirling flow tends to exert a positive effect to the rotor efficiency, whereas the positive swirling flow leads to a higher entropy generation in rotor passage.

Numerical investigation on effects of low Reynolds number conditions on fan shaped film cooling performances

This study investigates the effects of low Reynolds number (Re) conditions on the cooling performance of fan-shaped film cooling holes in the gas turbine engines of high-altitude long-endurance Unmanned Aerial Vehicles (UAVs). The significance of film cooling technology becomes paramount due to the low Re operational environment of UAVs. A novel Very Large Eddy Simulation (VLES) method was employed to systematically analyze a range of mainstream Reynolds numbers (ReD) from 480 to 32 000 and blowing ratios (M) from 1.0 to 2.5 while keeping the density ratio (DR) constant at 1.75. Compared to other turbulence models, the VLES model showed the highest similarity in predicting thermal field distributions and the most accurate prediction of film cooling performance at low Re. The results reveal that at low ReD, significant flow concentration within the hole leads to reduced velocity uniformity at the outlet, resulting in poor film coverage downstream. Additionally, the coolant jet tends to detach from the wall, adversely affecting cooling performance. In contrast, higher ReD exhibited improved coolant jet adhesion to the wall and cooling efficiency, attributed to the reduced intensity of counter-rotating vortex pair and decreased hot gas entrainment, thereby enhancing cooling effectiveness. Notably, for the same ReD values, cases with M = 1.5 consistently showed better cooling effectiveness compared to other M conditions. This study provides new insight into the cooling performance of fan-shaped film cooling holes under low Reynolds number conditions, which is crucial for enhancing the cooling efficiency of gas turbines in high-altitude UAVs.

Pitch Mathematical Modeling and Dynamic Analysis of a HALE UAV with Moving Mass Control Technology

Moving mass control (MMC) is considered a promising approach to regulating the attitude of an aircraft via the motion of internal moving masses. The present investigation proposes a moving mass control scheme for a high-altitude long-endurance (HALE) unmanned aerial vehicle (UAV) with a single slider moving longitudinally. To that end, a longitudinal nonlinear motion model is established, and pitch dynamics are analyzed. Furthermore, the influence of the slider parameters on the dynamic characteristics of the UAV and the change in control efficiency with speed are analyzed. Finally, a detailed root-locus-based stability and sensitivity analysis of the proposed control scheme is formulated. At an altitude of 20,000 m, the MMC scheme’s efficiency coefficient was 200% of that of elevator scheme at the cruise speed. The simulation results show that the control efficiency of the moving mass control scheme was significantly higher than that of the traditional elevator control scheme under the conditions of high altitude and low speed.

Neural Network and Dynamic Inversion Based Adaptive Control for an HALE-UAV against Icing Effects

In the past few decades, in-flight icing has become a common problem for many missions, potentially leading to a reduction in control effectiveness and flight stability, which would threaten flight safety. One of the most popular methods to address this problem is adaptive control. This paper establishes a dynamic model of an iced high-altitude long-endurance unmanned aerial vehicle (HALE-UAV) with disturbance and measurement noise. Then, by combining multilayer perceptrons (MLP) with a nonlinear dynamic inversion (NDI) controller, we propose an MLP-NDI controller to compensate for online inversion errors and provide a brief proof of control stability. Two experiments were conducted: on one hand, we compared the MLP-NDI controller with other typical controllers; on the other hand, we evaluated its robustness and adaptiveness under different icing conditions. Results indicate that the MLP-NDI controller outperforms other typical controllers with higher tracking accuracy and exhibits strong robustness in the presence of icing errors and measurement noise, which has huge potential to ensure flight safety.

SIMU/Triple star sensors integrated navigation method of HALE UAV based on atmospheric refraction correction

AbstractTo achieve autonomous all-day flight by high-altitude long-endurance unmanned aerial vehicle (HALE UAV), a new navigation method with deep integration of strapdown inertial measurement unit (SIMU) and triple star sensors based on atmospheric refraction correction is proposed. By analysing the atmospheric refraction model, the stellar azimuth coordinate system is introduced and the coupling relationship between attitude and position is established. Based on the geometric relationship whereby all the stellar azimuth planes intersect on the common zenith direction, the sole celestial navigation system (CNS) method by stellar refraction with triple narrow fields of view (FOVs) is studied and a loss function is built to evaluate the navigation accuracy. Finally, the new SIMU/triple star sensors deep integrated navigation method with refraction correction upgraded from the traditional inertial navigation system (INS)/CNS integrated method can be established. The results of simulations show that the proposed method can effectively restrain navigation error of a HALE UAV in 24 h steady-state cruising in the stratosphere.

High altitude long endurance of unmanned aerial vehicle (UAV) ITB solar panel conceptual design

One of the factors for the long endurance of high altitude long endurance (HALE) of an unmanned aerial vehicle (UAV) that belong to Institut Teknologi Bandung, Indonesia or called as HALE UAV ITB is the design of battery and solar panel. This paper discusses the method to calculate battery and solar panel requirements for HALE UAV ITB to fly for more than 24 hours at 20.000 feet. Several designs, configuration, and type of solar panels are analysed to fulfil HALE UAV ITB requirements. The variable compared is solar panel area, weight, and types. As a result, the use of Monocrystalline Silicone solar cell was found to be much more efficient than Polycrystalline Silicon, CIGS Thin Film, and Amorphous Silicon Thin Film with power generated per area of 224 Watt/m2 and power per weight of 436 Watt/kg. The minimum area required for a Monocrystalline Silicone type solar cell to generate power is 5.94 m2 with a total cell weight of 5.31 kg.

State Estimation for HALE UAVs With Deep-Learning-Aided Virtual AOA/SSA Sensors for Analytical Redundancy

High-altitudelong-endurance (HALE) unmanned aerial vehicles (UAVs) are employed in a variety of fields because of their ability to fly for a long time at high altitudes, even in the stratosphere. Two paramount concerns exist: enhancing their safety during long-term flight and reducing their weight as much as possible to increase their energy efficiency based on analytical redundancy approaches. In this letter, a novel deep-learning-aided navigation filter is proposed, which consists of two parts: an end-to-end mapping-based synthetic sensor measurement model that utilizes long short-term memory (LSTM) networks to estimate the angle of attack (AOA) and sideslip angle (SSA) and an unscented Kalman filter for state estimation. Our proposed method can not only reduce the weight of HALE UAVs but also ensure their safety by means of an analytical redundancy approach. In contrast to conventional approaches, our LSTM-based method achieves better estimation by virtue of its nonlinear mapping capability.

Optimal Design of Outer-Rotor Surface Mounted Permanent Magnet Synchronous Motor for Cogging Torque Reduction Using Territory Particle Swarm Optimization

In this paper, territory particle swarm optimization (TPSO) is proposed for the optimal design of surface mounted permanent magnet synchronous motor (SPMSM) for high altitude long endurance (HALE) unmanned aerial vehicle (UAV). The proposed algorithm exploits the concept of a territory to the particle swarm optimization (PSO) to solve the problem that the conventional PSO cannot find the multimodal solutions. Also, by combining the stochastic method, PSO, with the deterministic method, pattern search method, it is possible to find optimal solutions quickly and accurately. The superiority of the proposed algorithm is verified through comparison in the test functions with niching genetic algorithm, which is well known multimodal optimization algorithm. The TPSO is applied to the optimization design of outer-rotor SPM for HALE UAV, and the optimal design with reduced cogging torque has been derived.

Study of Simulation Platform for BDS/INS/CNS Deep Integration Navigation

In this paper, INS/CNS (CINS) is integrated into a module, and then CINS and BDS are further combined to form a deep integrated BDS/INS/CNS navigation system, which can significantly improve the navigation, positioning, and attitude measurement accuracy under high dynamic and strong interference conditions. It has broad application prospects for specific users such as high-altitude long-endurance Unmanned Aerial Vehicle (UAV) and high-maneuvering glider. In order to verify and analyze the algorithm and performance of the deep integrated navigation system, the design and implementation of BDS/INS/CNS deep integrated navigation simulation platform are presented and the overall architecture, information flow, and the composition of each subsystem of the simulation platform are introduced. The simulation results show that, under high dynamic conditions, the position accuracy of the BDS/INS/CNS deep integrated navigation system is better than 1 m, the speed accuracy is better than 0.1 m/s, and the overall performance is better than the BDS/INS deep integrated navigation system. It also verifies the availability of the simulation platform, which has guiding significance for the next design of BDS/INS/CNS deep integrated navigation prototype.

Aerodynamic Model-Aided Estimation of Attitude, 3-D Wind, Airspeed, AOA, and SSA for High-Altitude Long-Endurance UAV

This article proposes a novel dynamic model-aided navigation filter to estimate the safety-critical states of an aircraft including the effect of wind. Aerodynamic coefficients and control signals are used to predict the angular rates. Experimental flight results of a high-altitude long-endurance unmanned aerial vehicle (UAV) demonstrated improvement in attitude estimation compared to a model-based navigation algorithm that does not consider wind, as well as accurate attitude estimation without using gyroscope signals, demonstrating its effectiveness for analytical redundancy.

Aeroelastic energy harvesting from statistically representative gust encounters

The mission of high-altitude long-endurance unmanned aerial vehicles is limited by energetic considerations. This paper explores, for the first time in the open literature, statistic estimates of the potential energy that may be harvested from gust encounters along a representative flight mission. The work is built around three objectives: (1) investigate the influence that the configuration of the piezoelectric inserts, at equivalent total mass, has on the energy harvesting performance; (2) assess the energetic balance between the harvested energy from gust encounters and the energy needed by an actuation system to achieve a certain gust load alleviation; and (3) discuss the potential weight saving of batteries when employing piezoelectric inserts. The test case is for the flexible wing of a high aspect ratio unmanned air vehicle flying at low speeds.

Outage probability based on telecommunication range for multi-hop HALE UAVs

Cooperative relaying increases telecommunication range, improves the connectivity, and increases the reliability of data transmission; however, the transmitted power does not change. This paper analyzes the extended telecommunication range of a multi-hop cascaded network comprising N–cooperative relaying high-altitude long endurance (HALE) unmanned aerial vehicles (UAVs) under ambient conditions. A notable ambient condition is rain, which causes signals to scatter in different directions; hence, one should model the communication channel for HALE UAV as a Rayleigh channel. This paper proposes a statistical model that is based on the effect of the telecommunication range on the outage probability in an N-Rayleigh fading channel. The simulation results show that as the telecommunication range increases, the outage probability (Poutage) also increases, whereas when both the telecommunication range and the number of relays increase, Poutage decreases. An issue that has been highlighted in this paper is that, by increasing number of relays from N=1 to N=5 the telecommunication range increases and Poutage about 40% decreases. Moreover, in rainy conditions and with a fixed number of relays, when both the intensity of rainfall and telecommunication range increases, Poutage increases. For example by increasing rate of rain (Rr) from 1mm/h to 100 mm/h, Poutage increases around 30% in 100 Km with two relays.

Design and Performance Evaluation of Propeller for Solar-Powered High-Altitude Long-Endurance Unmanned Aerial Vehicle

Design, wind tunnel test, computational fluid dynamics (CFD) analysis, and flight test data analysis are conducted for the propeller of EAV-3, which is a solar-powered high-altitude long-endurance unmanned aerial vehicle developed by Korea Aerospace Research Institute. The blade element momentum theory, in conjunction with minimum induced loss, is used as a basic design method. Airfoil data are obtained from CFD analysis, which takes into account the low Reynolds number effect. The response surface is evaluated for design variables by using design of experiment and kriging metamodel. The optimization is based on desirability function. A wind tunnel test is conducted on the designed propeller. Numerical analyses are performed by using a commercial CFD code, and results are compared with those obtained from the design code and wind tunnel test data. Flight test data are analyzed based on several approximations and assumptions. The propeller performance is in good agreement with the numerical and measurement data in terms of tendency and behavior. The comparison of data confirms that the design method, wind tunnel test, and CFD analysis used in this study are practically useful and valid for the development of a high-altitude propeller.

Experimental Study on Calendaristic Degradation and Self-Discharge of 3.4 Ah Lithium-Sulfur Pouch Cells

Lithium-Sulfur (Li-S) batteries represent one of possible development pathways of Lithium based batteries, which are expected to provide benefits of high volumetric energy density, various safety features and low production cost 1. Already nowadays, one can find demonstrated applications, which heavily depend on unique attributes of Li-S batteries, e.g. high-altitude long-endurance unmanned aerial vehicles capable to endure for an extended periods of time in air (currently proofed for 14 day without landing) 2. However, wide commercialization of Li-S batteries is still hindered mainly by their limited performance and short lifetime 3. Both, cycling and storage, influence the Li-S battery lifetime. The degradation is often assigned to the irreversible relocation of polysulfides, which results into the corrosion of lithium metal anode, degradation of sulfur cathode and surface passivation of both electrodes 4. These degradation aspects were studied and discussed in literature into a certain degree; however, as pointed out in Ref. 3, some observations are possible to be done only at commercial-size cells, instead at coin cells, which determines the further focus of this work on a larger format cells, specifically pouch cells. The Li-S pouch cells were previously studied for an effect of cycling degradation on sulfur cathodes 5 and lithium metal anodes 6. The current study brings an experimental investigation of a capacity fade and a self-discharge with a periodic one month checking for storage of Li-S cells at various conditions of state-of-charge and temperature. The methodology presented in Ref. 7 is used for evaluation of the battery performance during the degradation in terms of capacity, resistance, power capability and shuttle current. M. Wild, L. O’Neill, T. Zhang, R. Purkayastha, G. Minton, M. Marinescu, and G. J. Offer, Energy Environ. Sci., 8, 3477–3494 (2015).http://defence.airbus.com/portfolio/uav/zephyr/, accessed at 20th November 2017.T. Cleaver, P. Kovacik, M. Marinescu, T. Zhang, and G. Offer, J. Electrochem. Soc., 165, A6029–A6033 (2018).S.-H. Chung and A. Manthiram, ACS Energy Lett., 1056–1061 (2017).S.-E. Cheon, S.-S. Choi, J.-S. Han, Y.-S. Choi, B.-H. Jung, and H. S. Lim, J. Electrochem. Soc., 151, A2067 (2004).X. B. Cheng, C. Yan, J. Q. Huang, P. Li, L. Zhu, L. Zhao, Y. Zhang, W. Zhu, S. T. Yang, and Q. Zhang, Energy Storage Mater., 6, 18–25 (2017).V. Knap, D. I. Stroe, R. Purkayastha, S. Walus, D. J. Auger, A. Fotouhi, and K. Propp, ECS Trans., 77, 479–490 (2017). Figure 1

Solar Cell to Support Perpetual Flight of High Altitude Long Endurance UAV ITB

Research on a High Altitude Long Endurance (HALE) Unmanned Aerial Vehicle (UAV) is currently being conducted at Bandung Institute of Technology to reach the flight duration needed and to get the solution of today’s challenges, minimizing pollution. Besides the good aerodynamic efficiency needed, energy resource is now becoming important. The energy resource must have a good endurance, easy to get, and of course, less pollution. Discussion in this paper is about the analysis of power needed by HALE UAV while takeoff and cruise flight conditions, and then determine the amount of solar cell and battery needed by the UAV.

Comparative Study of Wing Lift Distribution Analysis for High Altitude Long Endurance (HALE) Unmaned Aerial Vehicle

The development of High Altitude Long Endurance (HALE) Unmanned Aerial Vehicle (UAV) has been emerged for both civil and military purposes. Its ability of operating in high altitude with long endurance is important in supporting maritime applications.Preliminary analysis of HALE UAV lift distribution of the wing presented to give decisive consideration for its early development. Ensuring that the generated lift is enough to compensate its own weight. Therotical approach using Pradtl’s non-linear lifting line theory will be compared with modern numerical approach using Computational Fluid Dynamics (CFD). Results of wing lift distribution calculated from both methods will be compared to study the reliability of it. HALE UAV ITB has high aspect ratio wing and will be analyze at cruise flight condition. The result indicates difference between Non-linear Lifting Line and CFD method.

Design of High Altitude Long Endurance UAV: Structural Analysis of Composite Wing using Finite Element Method

Research on a High Altitude Long Endurance (HALE) Unmanned Aerial Vehicle (UAV) is currently being conducted at Bandung Institute of Technology (ITB). Previously, the 1st generation of HALE UAV ITB used balsa wood for most of its structure. Flight test gave the result of broken wings due to extreme side-wind that causes large bending to its high aspect ratio wing. This paper conducted a study on designing the 2nd generation of HALE UAV ITB which used composite materials in order to substitute balsa wood at some critical parts of the wing’s structure. Finite element software ABAQUS/CAE is used to predict the stress and deformation that occurred. Tsai-Wu and Von-Mises failure criteria were applied to check whether the structure failed or not. The initial configuration gave the results that the structure experienced material failure. A second iteration was done by proposing a new configuration and it was proven safe against the load given.

Deformation Control of Highly Flexible Aircraft in Trimmed Flight and Gust Encounter

High-altitude long-endurance unmanned aerial vehicles are inherently highly flexible, and therefore are more susceptible to very large structural deformation in trimmed flight and in atmospheric turbulence. This work aims to avoid these large wing deformations by incorporating and deflecting multiple redundant control surfaces along the leading and trailing edges of the wing. These surfaces are used in both trim optimization to constrain wing deformation to a user-defined value in steady trimmed flight and in minimizing the dynamic response to gust encounter via a feedback controller. Trim optimization is performed using the simplex algorithm. Concurrently, a robust control scheme is designed and applied using loop shaping to demonstrate that, although the control surfaces are used for trimming the aircraft, they have enough authority left to effectively minimize elastic wing deformations during gust penetration. The aforementioned methodology is demonstrated on a highly flexible flying wing. Trim optimization effectively allows trimmed flight at various load factors in the flight envelope while maintaining small structural deformations. The designed controller significantly reduces the maximum wing deflection experienced by a gust disturbance, which is bounded below a user-specified value.

Study of Aerodynamic and Heat-Exhaust Characteristics for a High-Altitude Long-Endurance Unmanned-Aerial-Vehicle Airfoil

This paper identifies exhaust heat characteristics depending on airfoil shapes at low Reynolds number to design a high-altitude long-endurance unmanned aerial vehicle with a wing-surface heat exchanger. In the first step, computational fluid dynamics simulations are conducted for different airfoils, each of which exhausts heat from different regions on the upper surface, at different angles of attack. This parametric study reveals that early transition near the leading edge is favorable to improve heat-exhaust characteristics, although it may increase skin friction. In addition, heat exhaust should be conducted only in the region of turbulent boundary layer behind the transition point. From these results, the airfoil shape significantly affects the Nusselt-number distribution along the upper wing surface due to the change in the location of laminar–turbulent transition and turbulent boundary-layer separation. In the next step, multi-objective optimization of an airfoil shape, which balances aerodynamic performance and heat-exhaust performance, is carried out. The obtained nondominated solutions show the tradeoffs between aerodynamic performance and heat-exhaust performance. It was confirmed that heat-exhaust performance can be controlled by the location of the laminar–turbulent transition, and improved without sacrificing aerodynamic performance at the cruising condition.

Parameter’s sensitivity analysis and design optimization of solar-powered airplanes

Purpose The purpose of this study is to present a methodology for parameters’ sensitivity analysis of solar-powered airplanes. Design/methodology/approach The study focuses on a preliminary design and parameters’ relations of a heavier-than-air, solar-powered, high-altitude long-endurance unmanned aerial vehicle. The methodology is founded on the balance of energy production and requirement. An analytic expression with four generalized parameters is derived to determine the airplane flying on the specific altitude. The four generalized parameters’ sensitivities on altitude are then analyzed. Finally, to demonstrate the methodology, a case study is given on the parameters’ sensitivity analysis of a prototype solar-powered airplane. Findings When using the presented methodology, the nighttime duration and the energy density of batteries are more sensitive on flight altitude of the prototype airplane. Practical implications It is not easy to design a solar-powered airplane to realize high-attitude and long-endurance flight. For the current state-of-art, it is a way to figure out the most critical parameters which need prior consideration and immediate development. Originality/value This paper provides an analytical methodology for analyzing the parameters’ sensitivities of solar-powered airplanes, which can benefit the preliminary design of a solar-powered airplane.