# Introduction nmanned Aerial Vehicle has become an active research area due to the vehicles drastically making a difference in versatile field, such as remote sensing, reconnaissance, surveillance, disaster relief, mineral exploration, military forces, search and rescue. The advent of small UAVs (MAV) has made the task much simpler than large UAVs. Moreover the small UAVs are portable in a bag pack i.e., they follow the break apart system which is useful in the time of emergency situations. The early biplane configuration is well known, which has a pair of wings one over the other making low aspect ratio high agility aircrafts possible but had a drawback of interference effect, to be specific. By replenishing and modifying this order version for better aerodynamic performance, a tandem wing arrangement is adopted in which the wings are placed one behind the other. This arrangement is chosen because of its increased number of lifting surfaces. Along with the developments of smaller UAVs, termed mini UAVs, has come issues involving the endurance of the aircraft. Endurance in mini UAVs is An airplane in motion through the atmosphere is responding to the "four forces of flight" --lift, drag, thrust and weight. Just how it responds to these four forces, determines how fast it flies, how high it can go, how far it can fly, and so forth. These are some of the elements of the study of airplane performance by [3] "John Anderson" on his 7 th Edition of Introduction to flight book. He further said that, an aircraft should be stable in order to come back to its equilibrium position after when it is deviated from its flight path. Highly stable aircraft requires powerful control to take the aircraft from one equilibrium to other. This paper will focus on quantifying the energy available from ambient sunlight and the UAVs performance and stability study. On considering problematic because of the limited size of the fuel systems that can be incorporated into the aircraft. Energy harvesting is an attractive technology for mini UAVs because it offers the potential to increase their endurance without adding significant mass or the need to increase the size of the fuel system. This paper will focus on the aerodynamic analysis and construction of sUAV using ambient sunlight. The concept of analyzing two wing configurations termed as Tandem Aircraft will provide better aerodynamic characteristics at low Reynolds Number than conventional aircraft. The merits of such arrangements are payload can be increased because of two low aspect ratio wings, lift produced is more than the conventional aircraft, and cruising velocity is high. The maximum flight duration of unmanned aerial vehicles varies widely. "In 2007, Scientists André Noth, Roland Siegwart, and Walter Engel" [1] proposed from their research that solar electric UAVs hold the potential for unlimited flight. Further, they expiated on how these Solar Powered Micro Vehicle uses the energy obtained from the sun through the solar cells installed on the surface areas of the aircraft model that is going to be designed. Solar Powered MAV is an emerging field of flight research aimed towards attaining limitless endurance to explore vast areas in a single flight whereas solar powered flights will develop from MAV's into huge stable flights travelling in the future and helps make flight travelling ecofriendly and economical which is an innovative initiative said by "C.K.Patel, H.Arya and K.Sudhakar" [2] on the International Seminar and Annual General Meeting of the Aeronautical Society of India presentation where they presented their work on design, build and fly a Solar Powered Aircraft held at 2002. the above said merits, the project takes the path towards the design and analysis of tandem wing configuration sUAV. # II. Preliminary Design From the Literature survey, it is identified that the small unmanned aerial vehicle used for the purpose of surveillance is mostly reliable and simple. Initially, the dimensions and parameters of sUAV were identified for the design. The wing span is around 2m which is the special feature of sUAV for the tandem wing arrangement and moreover the length of the sUAV is about 1.8 m. The tandem wings are also suggested to be placed at a distance where the interaction is to be low. Therefore different horizontal arm distances are considered viz., 3 times the chord (3c), 5 times the chord (5c). Similarly the width of the fuselage is calculated to be around 0.15m, based on accommodating the components like electric motor, GPS, etc. By taking this into account, the vertical arm distances are categorized into 0c, 0.5c, 1c. Among these distances, one of the combinations is chosen using analysis. The wing loading for this tandem arrangement is calculated by doing simple weight estimation and the resultant value comes out to be 4.55kg/m 2 . The aspect ratio is considered to be in the range of 4 to 6 for a small aerial vehicle and hence AR is assumed to be 4. From the AR, the chord of the airfoil is determined to be 250 mm. Now the dimensions are found accordingly and the 2D design is triggered with brief estimation from [4] "Daniel P. Raymer" book on Aircraft Design: A Conceptual Approach shown in Fig1. # a) Wing Planform Analysis The aerofoil selected for the wing is the low drag laminar series NACA 65 1 212 with reference from the NASA Contractor Report 165803 by [5] "Carmichael, B. H" on Low Reynolds number airfoil survey on November 1981. This series is chosen due to the following reasons: 1. High maximum lift coefficient 2. Very low drag over a range of operating conditions 3. Increased laminar zone for the flight Reynolds number. The significance of having two main wings is to be deeply studied for its aerodynamic efficiency because of its difference from the pure aerodynamic design. To start with, the airfoil sketch is made for the analysis work exclusively designed at the aerodynamic efficiency results. Several combinations are chosen for the design such as 3c-0c, 3c-0.5c, 3c-1c, 5c-0c, 5c-0.5c, 5c-1c, where c represents the chord of the airfoil as mentioned in Fig2. From the analytical results, the tandem wings are decided to be located at 5c-0c & 0.5c distance. This project deals with the tandem configuration of a fixed wing aircraft where there are two wings. One is placed at lower, front side and the other is placed at higher, rear side. The Wing structure consists of front and rear spars of dimension 10 x 8 mm and 11 ribs which are placed at equal spacing between each other. The front spar is placed at 15% of the chord distance and the rear spar is placed at 65% of the chord distance. The spars and ribs are then covered with a fabric cloth which then doped with nitro cellulose solution to increase the stiffness of the screen as indicated in Fig3. # b) Fuselage Analysis The fuselage design is initially considered to have different shapes but the finalized design is one having a simple shape with low drag making it easy for fabrication for further wind tunnel testing. Therefore the fuselage design starts with a simple square shape with a nose ensuring the streamlined flow over the entire body. This can even be suitable for the motor fixation. The dimensions of the fuselage are set according to the Year 2017 # c) Wing-Fuselage Attachment Design The major challenge is to attach the wing model to the above mentioned fuselage design. The attachment should be made such that wing and fuselage should hold together firmly and should not vibrate or deviate from its position while acting upon the loads and stresses. Hence while designing the wing, about 5 cm clearance has been given to both the front and rear spars which will be used as a portion to attach the entire wing into the fuselage. The spar box designed where wing's spars will be directly inserted into the hole and then joined with special adhesives such that spar box and spar should not rotate or move independently. The integrating part of the wing and fuselage was shown in Fig5. # d) Weight Estimation A sUAV can be sized using some existing motor, battery and solar panel and other electronics. The existing motor, battery and solar panel are fixed in size and thrust. They can be scaled to any thrust so the thrust-to-weight ratio can be held to some desired value even as the SUAV weight is varied. This approach allows the designer to size the SUAV to meet both performance and range goals, by solving for takeoff gross weight while holding the thrust-to-weight ratio required meeting the performance objectives. In the weight estimation, the different components like solar panel, avionics, batteries, servos are considered in terms of surface area of the wing after performing comprehensive studies and estimations from 85 th volume of [6] The total weight of the aircraft is found to be 4.55 kg including the structural and solar panel weight of 2.55 kg. While calculating, the wing loading is assumed to be 4.55kg/m 2 , since it ranges from 4 to 6 kg/m 2 for slow fliers. From the known values, the wing area, wing span and aircraft length are estimated as 1m 2 , 2m and 1.8m. Choosing the thrust to weight ratio as 0.3 and considering the cruising altitude as 1.3km which is limited with the avionics, the required thrust is calculated to be 1.365 kg and the cruising thrust to be 1.1675 kg. The thrust required is estimated using the propulsion thrust bed test. The thrust bed is designed in order to have an experimental study over the thrust produced, using plywood board and rail movement mechanism as indicated in Fig6. # e) Airfield Requirements If the required runway length is too short, the aircraft cannot take-off with full fuel or full payload and the aircraft economics are compromised. The landing velocity depends upon the deceleration and landing distance. Landing distance has been estimated as per CAR regulations and chosen as 360 meter runway. The deceleration is usually taken as 0.18g and 0.2g if reverse thrust is applied. Then, the landing velocity and the stall velocity are estimated as 37.5851m/s and 32.6827m/s respectively. # f) Aircraft Performance Aircraft performance includes many aspects of the airplane operation. Here we deal with a few of the most important performance measures including airfield performance, climb and cruise. The ability of the aircraft to fly up and over obstacles depends critically on its climbing characteristics are compared and plotted various altitude as shown in Fig7. Time required reaching the cruising altitude by the airplane is determined by using the 1/(R/C) max vs Altitude plot. The Area under this plot gives the time to climb to cruising altitude as mentioned in Fig8. These # g) Endurance Endurance (E) is the time duration for which the Airplane can fly with maximum fuel and with maximum payload. Range (R) is the maximum Horizontal Distance Covered by an Airplane. Once endurance is known, Range (R) can be estimated by multiplying it with cruising velocity. Without the solar panel, the endurance is estimated to be 17 min. From the above values it's evident that the obtained value is higher than the assumed value. In order to increase the endurance, the solar panel is mounted on the surface of the wing with the reference to the [8] "Solar powered High Efficient Dual Buck Converter for Battery Charging" journal by EstherGlory.S, Dhivya.P.S, Sivaprakasam.T. # III. # Discussion of Test Results The aerodynamic and performance characteristics of sUAV had done by two analyses: CFD analysis and Wind Tunnel analysis with scaled model. # a) CFD Analysis Computational fluid dynamics (CFD) is a tool that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows. The geometry of the airfoil is initially sketched in CATIA V5R20 by importing the NACA 65 1 212 airfoil coordinates and suitable size of rectangular domain is drawn. The domain with the airfoil is then meshed with a fine dimensional grid. The meshed airfoil is read in ANSYS FLUENT and the grids were checked. The main scope of the analysis is to find the airfoil combination having: 1. Greater Aerodynamic efficiency 2. Less interaction 3. Acceptable aerodynamic center shift Using Ansys Fluent, the above different combinations are analyzed for aerodynamically efficiency combinations. The algorithm and theoretical study for the research were carefully studied from research journal named [9] "An introduction to theoretical and computational aerodynamics" by Moran Jack and Dover. P. The domain is drawn accordingly by giving opening boundary condition. The velocity is calculated to be 12m/s. For different angles of attack the domain is kept constant and the direction of the flow is changed with respect to the chord line. From the analyses, the forces and moments over each airfoil are calculated. The contours and the flow patterns across each airfoil are depicted below for all the combinations. Initially the 6 combinations of airfoil locations are considered and the analysis is made determining the total lift and drag. From this substantial analysis, the combination was confined which is having good aerodynamic efficiency, smaller shifts in aerodynamic center and further taken to the design for 3D layout as shown in Fig9. # b) Aerodynamic Efficiency The lift and drag values across the front airfoil (A1) and the aft airfoil (A2) are tabulated along with the total lift and drag using wind tunnel balance. For different angles of attack the forces are resolved to get Year 2017 The determination of aerodynamic centre plays a key factor in the stability of the aircraft. Thus before taking the maximum C L and minimum C D values into account for design from the previous analysis, it is important to carry out the analysis for minimum shift in aerodynamic centre. By choosing the configuration with minimum shift in aerodynamic centre, CG is fixed and the design process is then carried out. The mesh files used for analysis of different wing arrangements is again used for the determination of aerodynamic centre. The graphs are plotted between the pitching moment coefficients and the distance at which they are calculated from the leading edge as shown in Fig13. From the graphs, the shift in aerodynamic centre is calculated from which the one with least is chosen. The shift in moment is less for the 3c combination but comparing this with the interaction analysis using the velocity and streamline patterns, 3c combination has more interactions while comparing with 5c. Therefore, the 5c-0.5c combination is selected because of its acceptable shift in ac and less interactions depicted by the following contours at different angles of attack as shown in Fig14. # d) Structural Stability Analysis of the Wing Members The structural stability analysis of the wing have been tested with computerized software such as Static structural analysis on ANSYS , Harmonic analysis on Nx -Nastran and also experimental load test on the wing structure. The wing analysis was carried out with the study of T.H.G Megson [11] The comparison between the spars have been made based on many factors such as cost effectiveness, market availability and required deflection and concluded that spar with dimension 10 x 8 x 1000 mm have been finalized. # e) Wind Tunnel Testing The lift and drag values have been obtained using 5c-0.5c scaled model which is fabricated in the material of wood. This model was tested by using the balance setup with the help of wind tunnel, the values were obtained by the software termed as SCAD 508 and the device named as PYRODYNAMICS where the values displayed in the monitor connected to the device as shown in Fig15. The angle of attack of the model was changed by using pitch-yaw controller setup which is available in our laboratory. The values taken for the following angle of attack: 0 0 , 5 0 , 10 0 and 15 0 . The values were tabulated and the graphs were plotted and compared with 2D analysis results as mentioned in Fig16. # f) Models Testing After the scrupulous testing and estimations with reference to [12] "Estimating R/C Model Aerodynamics and Performance" by Nicolai, Leland M, A remote controlled hobbyist aircraft was chosen as the test bed for this study because the aircraft is inexpensive and easy to assemble, spare parts are readily available, and the aircraft is on the same length and weight scale as some existing military UAVs. The test bed has been divided into two categories. First the test fly was made possible using the chloroplast sheet of 5mm thickness. The aircraft is constructed with an electric propulsion system composed of an electric motor and an 11. Finally, the prototype was made using glass fiber for wings and plywood for fuselage. Several modifications were performed on the original aircraft in order to include the photovoltaic energy device for generating alternative energy source as shown in Fig19. IV. # Conclusion An experimental study has been carried out to analysis the aerodynamic and performance characteristics of small unmanned aerial vehicle. The thrust required and available are determined by analyzing the characteristics of the given motor and also the power required has been determined for the unmanned aerial vehicle. The endurance of the aircraft is determined and increased by placing alternative solar energy power source. The structure of the aircraft was designed and analyzed through the software and compared with the results obtained from the wind tunnel. Based on the flight tests that have been performed, it can be concluded that the sUAV is effective in aerodynamic design and the solar energy device has the capability of charging energy storage devices with high endurance meticulously studied from, 1![Fig. 1: Tandem Wing sUAV Design](image-2.png "DFig. 1 :") 2![Fig. 2: (i) 3c-0c (ii) 3c-0.5c (iii) 3c-1c](image-3.png "Fig. 2 :") 3![Fig. 3: Wing Design](image-4.png "Fig. 3 :") !["SHAMPO: Solar HALE Aircraft for Multi Payload Operation" presented by G.Romeo, G.Frulla, E.Cestino and F. Borello to the Aerotecnica Missili & Spazio (Journal of the Italian Association for the Aeronautics and Astronautics) on Sep 2005. Simultaneously, motor and structural weights are considered in terms of percentage of total weight of the SUAV. W 0 = W solar panel + W structural + W avionics + W servo + W battery + W motor + W propeller](image-5.png "") 4![Fig. 4: Semi-Monocoque Fuselage Design](image-6.png "Fig. 4 :") 5![Fig. 5: Integrating fuselage with the wing](image-7.png "Fig. 5 :") 78![Fig. 7: Rate of Climb at various altitudes](image-8.png "DFig. 7 :Fig. 8 :") 9![Fig. 9: Contours of pressure coefficient and Velocity magnitude](image-9.png "Fig. 9 :") 11![Fig.11: AOA vs C D for 3c and 5c combinations](image-10.png "Fig. 11 :") ![Fig. 12: C L vs C D for 3c and 5c combinations](image-11.png "") 14![Fig. 14: Velocity Contours for 5c-0.5c](image-12.png "Fig. 14 :") ![Fig. 15: Structural analysis of wing](image-13.png "") 16![Fig. 16: Wind Tunnel Balance and Scaled Model](image-14.png "Fig. 16 :") 14![Fig. 20: Flight test of Tandem wing aircraft](image-15.png "[ 14 ]") © 2017 Global Journals Inc. (US) Year 2017 D © 2017 Global Journals Inc. (US) Real time Characteristics of Tandem Wing UAV D © 2017 Global Journals Inc. (US) Real time Characteristics of Tandem Wing UAV ## Acknowledgment We express our heartfelt thanks to the management for providing us with the necessary laboratory facilities and intellectual resources which were indispensable aids throughout the course of the project. We also express our gratitude towards Dr. P. Kasinatha Pandian, Principal for the freedom he gave us to complete the project. We extend our list of acknowledgement to Dr. Dharmahinder Singh Chand, Professor and Head of the Department and project supervisor for providing guidance and clarification whenever needed throughout the project. We also thank our entire faculty members to make realize our mistakes, mis-conception and to lead us in a correct way during our course of project. We have an immense pleasure in thanking Dr.P.Baskaran, Professor of Eminence and Dr. K. Vijayaraja and Mr. U. Nirmal Kumar, for sharing their ideas and suggestions throughout our course of project. We extend our gratitude to LARSEN & TOUBRO LIMITED, Solar business & the water renewable energy resources, Chennai for providing technical support offered for the accomplishment of this project. ## Appendix * Design of Solar Powered Airplanes for Continuous Flight ANoth RSiegwart WEngel December 2007 Version 1.1 * Design, Build and Fly a Solar Powered Aircraft CKPatel HArya KSudhakar International Seminar and Annual General Meeting of the Aeronautical Society of India 2002 * JohnAnderson 2010 McGraw-Hills Companies, Inc 7 th Edition "Introduction to flight * Raymer, President, Conceptual Research Corporation PDaniel Sylmar, California Aircraft Design: A Conceptual Approach * Low Reynolds number airfoil survey BHCarmichael 165803 November 1981 1 NASA Contractor Report * SHAMPO: Solar HALE Aircraft for Multi Payload Operation GRomeo GFrulla ECestino FBorello Aerotecnica Missile e Spazio 85 Sep 2005 * Preliminary reliability design of a solarpowered high-altitude very long endurance unmanned air vehicle Frulla Proceedings of the Institute of Mechanical Engineers the Institute of Mechanical Engineers 2002 216 * Solar powered High Efficient Dual Buck Converter for Battery Charging SEstherglory .PDhivya Sivaprakasam International journal of Innovative Research 1 9 December 2013 * An introduction to theoretical and computational aerodynamics MoranJack PDover 2003 * Fundamentals of Aerodynamics JDAnderson Jr 2001 McGraw Hill * Introduction to Aircraft Structural Analysis THMegson October 2013 * Estimating R/C Model Aerodynamics and Performance LelandMNicolai Lockheed Martin Aeronautical Company 2009 * Micro-air-vehicles: Can they be controlled better MGad-El-Hak Journal of Aircraft 38 3 June 2001 * Solar-Powered Unmanned aerial vehicles KCReinhardt TRLamp JWGeis AJCollozza 31 st International Energy Conversion Engineering Conference Aug 1996 IECEC