JOURNAL OF SCIENCE & TECHNOLOGY * No. 94 . 2013
DESIGN, FABRICATION AND TESTING OF AN AUTONOMOUS FIXED-WING UAV
THIET KE, CHE TAG VA THIT NGHIEM UAV CANH B A N G BAY Tl/DONG Nguyen Phu Hung*, Vu Quoc Huy, Dinh Tan Hung, Hoang Thi Kim Dung
Hanoi University of Science and Technology Received March 01,2013; accepted April 12, 2013
ABSTRACT
This paper ptosents design process, fabrication and flight testing of a micro fixed-wing Unmanned Aerial Vetiicle (UAV) that is capable of autonomous fligttt according to a predefimd trajectory The design process includes preliminary design, numerical simulations and wind-tunnel expetiments of the aerodynamic charactenstics of the UAV model. Autonomous control system hardware consists of a master board and a sensor board. The master board receives the data from tt sensor board, cames out the processing and sends the conttot commands to engine and servos. The UAV is fabncated and integrates the autopilot system. Autopilot flight tests with different trajectories validate the trajectory tracking capability with high accuracy of the developed UA V.
Key words Unmanned Aenal Vehicle, drone, UAV TOM TAT
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1. INTRODUCTION three main steps : preliminary design, In recent years, small and micro UAVs aerodynamic analysis and integration of are being used in a many applications both in autopilot system,
civil and in miUtary. Numerous studies on the 2.1 Preliminary design development of autonomous UAVs are reported _,
[l]-[3]. However, the design of a fully . . ™ ' prehminary design is based on tlie autonomous UAV that can perform real-world ''^"'"'=^' Probabtlities. In order to enable the application has many technical challenges [31. n-ajectory tracking, the UAV must be high In Vietnam, design and development of '"°'"'">' ^"'' P ° " ' " ' " ' " « ^ '"^^'"S' f"
autonomous UAV have just started from a few " " ' " " " S "f '^on'rol and transmission devices II recent years. '^ found that an acrobatic type is appropriate for
the mobility and complex trajectories.
2. DESIGN PROCESS OF A FIXED-WING
UAV Using the statistical probability method for the typical aerobatic airplanes, the In this study, the objective consists in preliminary configuration of the UAV is design and fabrication of one micro fixed-wing proposed as shown in figure I. The detail UAV that is capable of autonomous flight. The dimensions of the UAV are calculated from the majortechnical parameters of the UAV include required technical parameters. The basit the mass from 4 * 6 kg, the operation range specifications of the designed UAV Jtt from 0.5 - 1 km with the maximum cruise summarized in table I.
speed of 15 m/s. The design process includes
JOURNAL OF SCIENCE & TECHNOLOGY * No. 94 - 2013
Fig. 1. Designed UA V configuration Table 1 Designed UAV specifications Specifications
Maximum takeoff weight Airfoil
Wing span Wing area Aspect ratio Wing tip chord Wing root chord Mean aerodynamic chord Fuselage length Maximum fuselage height Maximum fuselage width Engine
Value 5 kg Eppler E475 1.6 m 0.497 m^
5.1 196 mm 473 mm 354 mm 1260 mm 226 mm 164 mm O.S 120AX 2.2. Aerodynamic analysis
Aerodynamic analysis is one of the most important tasks in the detailed design phase of UAV. In this study, two approaches are used including wind-tunnel experiment and Computational Fluid Dynamic (CFD) simulation. The obtain results from two approaches are compared in order to validate the relevant aerodynamic characteristics of the designed UAV.
In the experimental study, a scale model of the designed UAV (1 : 6.4) is fabricated and mounted in a low speed wind-tunnel [4]. Figure 2 shows the UAV model and the mounting using in experiments. The mounting allows the rotation of the model according to three different axes, corresponding to pitching, rolling and yawing angles. The model is held at one position using a screw mechanism.
Fig. 3. Locations of pressure taps [4j In order to measure the pressure distribution on the model surface, 35 pressure taps are provided on both sides, as shown in figure 3. From the pressure measurement at each location, the aerodynamic forces (lift, drag) and the pitching moments are determined for each surface section area i S . The total lilt, drag and pitching moments for whole surface area are then calculated.
w
Fig 4 Computational domain [5j
.lOURNAL OF SCIENCE & TECHNOLOGY 4 No. 94 - 2013 In the numerical study, the main purpose
is to predict the aerodynamics forces (lift, drag) and the pitching moments with reduced time and cost [5]. The Vi model of the flill scale UAV are used in simulation thank to the symmetric. To stabilize the prediction of forces and moment, the computational domain has the dimensions of 5L x 2L x 3.5 L as shown in figure 4 where L is the fuselage length. The inlet boundary condition is set as Velocity inlet and Pressure Outlet is applied for the outlet boundary. Meshing is generated using Gambit®
as shown in figure 5. The CFD simulation is solved by FLUENT solver with Realizable k-e turbulence model.
Both experiments and numerical simulations are carried out at the same operational conditions that are similar as the real flight conditions of the designed UAV.
Indeed, two categories of flight condition are investigated:
- Velocity inlet = 10 m/s, angle of attack (ADA) from -5" •- 30°.
- Angle of attack = 10°, velocity inlet from 5 - 1 5 m/s.
Figure 6 shows the results of lift coefficient (Cl), drag coefficient (Cd) and moment coefficient (Cd) in ftinction of the AOA (alpha) that are obtained from the numerical simulation (CFD) and from the experiments. It shows a quite good agreement I between the experimental and numerical results.
It is found that the stall angle of the airplane is around 20°. The aerodynamic efficiency diagram (Figure 7) shows the variation of the ratio Cl/Cd in function of the AOA. It is shown that the most efficient flight condition is achieved with the angle ofattack in the range of I 0 ° - 12"
Fig. 5. Gambit® meshing f5]
1 S
'.
*• - 0 1 -
•0 7
/ -If - - X
- 9 if^
i i ^
-^-
•-+
"
» «
* C i |ctB)
* Cd (dd)
• Cm [ctdl
• CllB<p]
X Cd (BKp) oCmlBitp)
Fig. 6. Aerodynamic coefficients To evaluate the aerodynamic quality, it should be necessary to consider the airflow structure around the UAV via the numerical simulation. It is observed that the turbulence occurs at the wing trailing edge and at the fuselage - wing intersection when the AOA exceeds 10°. The turbulence can result in the decrease of lift and eventually the stall if the
Fig. 7. Aerodynamic efficiencies UAV continues the operation at high AOA. It is found that, at AOA - T, the airflow around the UAV is streamlined and the turbulence density is rather small, the impact of the turbulence may be negligible (figure 8). Hence, it could be concluded that the best aerodynamic quali^^oi the designed UAV is achieved at AOA = 7°. \!
JOURNAL OF SCIENCE & TECHNOLOGY • No. 94 - 2013
3. INTEGRATION OF AUTOPILOT SYSTEM
For autonomous flight, an autopilot system is integrated into the developed UAV.
The autopilot hardware is built from two main components including a sensor board and a master board. The sensor board has the task of receiving the raw sensors data from accelerometers, magnetometers and gyroscopes and performing initial processing. The data then are transferred to the master board for complex processing using algorithms. The block diagram of the control svstem is shown in figure 9.
Fig. 9. '. 'iinlrol system urchilccliin.'.
The master board consists of an Atmega 2560 microcontroller from Atmel. Analog inputs include five channels: autopilot control, throttle, yaw, pitch and roll (figure 9). Four output channels serving for servo control (figure 9). The master board has also four serial port in which one is u.sed for a standard EM- 406 GPS connector. The sensor board includes all required sensors for aircraft stabilization and navigation: 3-axis accelerometer, three gyroscopes and a pressure sensor. The sensor
board has also a relay switch for cameras, lights or others payloads.
4. AUTOPILOT FLIGHT TESTING Many autopilot flight tests are carried out with different trajectories such as straight trajectory or circle trajectory. Figure 10 and figure 11 show respectively the flight test results for straight trajectory and circle trajectory In those figures, green points (1, 2, 3 ...) are predefined waypoints that are set by controller. Yellow line connecting all the green points is the required trajectory. The real flight path of the UAV is shown by blue line. The figure 10 shows that the trajectory tracking for the straight path is very good (coincidence of the yellow line and the blue line). The tracking error increases at the corners of the flight path but the UAV returns quickly lo the straight path. The figure 11 shows another performance of the UAV in the circle trajectory tracking. In this case, the UAV is requested to perform a circular flight around a predefined waypoint after an arbitrary flight. It is observed that the UAV has performed a correct circular flight path as shown by the blue lines.
^'S^^v-p^u..-;
I-"'!-^. 1(1. Siraigiii lnl|L^L•lor^^ iiiilopilo! \-\!
Fig. ,' I. Circle irajeciory autopHul ,'<
JOURNAL OF SCIENCE & TECHNOLOGY • No. 94 - 2013
5. CONCLUSIONS take more payload (cameras) for various _. . £ . ! _ • . - J . mission such as traffic surveillance or mapping,
Design, fabrication and autonomous ° flight tests of a fixed-wing UAV are carried out. Acknowledgements
The successful autopilot flight tests validate the ^,. , „ „ - ^ j u .L ,. ^ ,, , ,. , ., ~ This work was supported by the
na^nAxmntm^ rttAnlit^i if. m a l l nf. tha paj i i k i lif ir /\4 ' ' '
aerodynamic quality as well as the reliability of
the control system of the developed UAV^ Science and T e ^ h n o i o ^ v i e t n ™ "
Furthermore, the developed UAV is capable of
Government Project KC.03 of the Ministry of
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Author's address: Nguyen Phu Hung-Tel: 09102143 737-E-mail: [email protected] Hanoi University of Science and Technology
No.l Dai Co Viet Str., Ha Noi, Viet Nam