Design, construction and flight control of a quad tilt-wing unmanned aerial vehicle

Unmanned Aerial Vehicles (UAVs) are flying robots that are employed both in civilian and military applications with a steeply increasing trend. They are already used extensively in civilian applications such as law enforcement, earth surface mapping and surveillance in disasters, and in military missions such as surveillance, reconnaissance and target acquisition. As the demand on their utilization increases, novel designs with far more advances in autonomy, flight capabilities and payloads for carrying more complex and intelligent sensors are emerging. With these technological advances, people will find even newer operational fields for UAVs. This thesis work focuses on the design, construction and flight control of a novel UAV (SUAVI: Sabanci University Unmanned Aerial VehIcle). SUAVI is an electric powered compact size quad tilt-wing UAV, which is capable of vertical takeoff and landing (VTOL) like a helicopter, and flying horizontally like an airplane by tilting its wings. It carries onboard cameras for capturing images and broadcasting them via RF communication with the ground station. In the aerodynamic and mechanical design of SUAVI, flight duration, flight speed, size, power source and missions to be carried out are taken into account. The aerodynamic design is carried out by considering the maximization of the aerodynamic efficiency and the safe fiight characteristics. The components in the propulsion system are selected to optimize propulsion efficiency and fulfill the requirements of the control for a stable flight in the entire speed range. Simulation results obtained by ANSYS and NASA FoilSimII are evaluated and motor thrust tests are conducted during this optimization process. The power source is determined by taking the weight and flight duration into account. The wings and the fuselage are shaped iteratively in fluid flow simulations. Additionally, the verification of aerodynamic design and maneuverability are assessed in the wind tunnel tests on the half-body prototype. The mechanical structure is designed to be lightweight, strong and protective, and to allow easy assembly and disassembly of SUAVI for practical use. The safety factors in the mechanical system are determined using FEM analysis in ANSYS environment. Specimens of candidate composite skin materials are prepared and tested for lightness, strength and integrity in mechanical tests. The ready for flight prototype SUAVI is produced from the selected composite material. Dynamical model of SUAVI is obtained using Newton-Euler formulation. Aerodynamic disturbances such as wind gusts are modeled using the wellknown Dryden wind turbulence model. As the flight control system, a supervisory control architecture is implemented where a Gumstix microcomputer and several Atmega16 microcontrollers are used as the high-level and low- level controllers, respectively. Gumstix computer acts as a supervisor which orchestrates switching of low-level controllers into the system and is responsible for decision making, monitoring states of the vehicle and safety checks during the entire flight. It also generates attitude references for the low-level controllers using data from GPS or camera. Various analog and digital filters are implemented to smooth out noisy sensor measurements. Extended Kalman filter is utilized to obtain reliable orientation information by fusing data from low-cost MEMS inertial sensors such as gyros, accelerometers and the compass. PID controllers are implemented for both the high-level GPS based acceleration controller and the low-level altitude and attitude controllers. External disturbances are estimated and compensated by a disturbance observer. Real-time control software is developed for the whole fiight control system. SUAVI can operate in semi-autonomous mode by communicating with the ground station. A quadrotor test platform (SUQUAD: Sabanci University QUADrotor) is also produced and used for the initial performance tests of the fiight control system. After successful fiight tests on this platform, the control system is transferred to SUAVI. Performance of the flight control system is verified by numerous simulations and real flight experiments. VTOL and horizontal flights are successfully realized

Analysis of hydrodynamic lift for gas turbine oil brush seals /

Brush seals are used in gas Turbine engine applications for their effectiveness in controlling leakage flows between stationary parts and rotating shaft With their superior leakage performance, they are becoming the successor to the labyrinth seals, which have always been widely used since the first gas turbine engines. After gaining popularity in secondary flow air sealing, applications extended to more challenging oil and oil mist sealing locations. Due to high rotor surface speed oil temperature rise and coking become main issues in addition to leakage performance. While each bristle forms very small bearing surface. high rotor surface speed and viscous sealing medium provide sufficient hydrodynamic lift force to overcome bristle reaction forces. The gap generated between the bristle tips and the rotor surface determines the oil temperature rise and leakage rate. Due to shear thinning in oil sealing applications lift force is inversely correlated to oil temperature rise leading to a self-balancing effect with surface speed. The aim of a proper design for oil brush seals would be to keep the leakage at the minimum rate while avoiding excess oil temperature rise. Inherent complexity of bristles make calculation of hydrodynamic lift forces under a brush seal rather complicated. To avoid costly experimental investigations, a closed form analytical solution would prove very useful to compare candidate designs and to study what-if scenarios. This work investigates analytical solutions to hydrodynamic- lift clearance and bristle lift forces based on bearing theory. After a detailed discussion on short bearing approach, possible closed form solutions based on long bearing approach have been explored. A more comprehensive yet numerical solution based on finite beating approach has also been provided to compare and understand pressure and lifting force results. Analyses have been performed for effective constant oil viscosity. Shear thinning effect has been later introduced through use of published oil temperature data for various rotor surface speeds. As bristle tip clearance data are not available, validity of analytical the results have been evaluated using beam bending forces and experimental leakage flow data for various surface speeds. The results indicate that long bearing solution underestimates the oil lift force. Although more comprehensive, finite bearing solution requires the knowledge of axial deflection/bloom of the bristle pack. Simple yet functional, short bearing solution appears as a viable tool for seal designers to compare various seal designs before doing detail experimental evaluation on a plausible candidate. Finally, possible further work areas have been discussed

Robust hovering control of a quad tilt-wing UAV

This paper presents design of a robust hovering controller for a quad tilt-wing UAV to hover at a desired position under external wind and aerodynamic disturbances. Wind and the aerodynamic disturbances are modeled using the Dryden model. In order to increase the robustness of the system, a disturbance observer is utilized to estimate the unknown disturbances acting on the system. Nonlinear terms which appear in the dynamics of the vehicle are also treated as disturbances and included in the total disturbance. Proper compensation of disturbances implies a linear model with nominal parameters. Thus, for robust hovering control, only PID type simple controllers have been employed and their performances have been found very satisfactory. Proposed hovering controller has been verified with several simulations and experiments

Robust position control of a tilt-wing quadrotor

This paper presents a robust position controller for a tilt-wing quadrotor to track desired trajectories under external wind and aerodynamic disturbances. Wind effects are modeled using Dryden model and are included in the dynamic model of the vehicle. Robust position control is achieved by introducing a disturbance observer which estimates the total disturbance acting on the system. In the design of the disturbance observer, the nonlinear terms which appear in the dynamics of the aerial vehicle are also treated as disturbances and included in the total disturbance. Utilization of the disturbance observer implies a linear model with nominal parameters. Since the resulting dynamics are linear, only PID type simple controllers are designed for position and attitude control. Simulations and experimental results show that the performance of the observer based position control system is quite satisfactory

İnsansız hava araçları için test düzeneği tasarımı ve üretimi

Boyutları kullanım amaçlarına göre değiskenlik gösteren insansız hava araçlarının (ĐHA), mekanik, elektronik ve yazılım alanlarında birçok yenilikler getiriyor olması bu konuda çalısan arastırmacıların günden güne daha çok ilgisini çekmektedir. Bu çalısmada, bir ĐHA için kontrol algoritmalarının test edilebileceği bir düzeneğin tasarım ve üretimi anlatılmıstır. Düzeneğin üretilmesini takiben gerekli dayanıklılık testleri yapılmış ve benzetimlerle örtüşen dayanıklılık sonuçları elde edilmistir

LQR and SMC stabilization of a new unmanned aerial vehicle

We present our ongoing work on the development of a new quadrotor aerial vehicle which has a tilt-wing mechanism. The vehicle is capable of take-off/landing in vertical flight mode (VTOL) and flying over long distances in horizontal flight mode. Full dynamic model of the vehicle is derived using Newton-Euler formulation. Linear and nonlinear controllers for the stabilization of attitude of the vehicle and control of its altitude have been designed and implemented via simulations. In particular, an LQR controller has been shown to be quite effective in the vertical flight mode for all possible yaw angles. A sliding mode controller (SMC) with recursive nature has also been proposed to stabilize the vehicle’s attitude and altitude. Simulation results show that proposed controllers provide satisfactory performance in achieving desired maneuvers

Modeling and position control of a new quad-rotor unmanned aerial vehicle with tilt-wing mechanism

In this work a dynamic model of a new quadrotor aerial vehicle that is equipped with a tilt-wing mechanism is presented. The vehicle has the capabilities of vertical take-off/landing (VTOL) like a helicopter and flying horizontal like an airplane. Dynamic model of the vehicle is derived both for vertical and horizontal flight modes using Newton-Euler formulation. An LQR controller for the vertical flight mode has also been developed and its performance has been tested with several simulations

Dynamic model and control of a new quadrotor unmanned aerial vehicle with tilt-wing mechanism

In this work a dynamic model of a new quadrotor aerial vehicle that is equipped with a tilt-wing mechanism is presented. The vehicle has the capabilities of vertical take-off/landing (VTOL) like a helicopter and flying horizontal like an airplane. Dynamic model of the vehicle is derived both for vertical and horizontal flight modes using Newton-Euler formulation. An LQR controller for the vertical flight mode has also been developed and its performance has been tested with several simulations

Mathematical modeling and vertical flight control of a tilt-wing UAV

This paper presents a mathematical model and vertical flight control algorithms for a new tilt-wing unmanned aerial vehicle (UAV). The vehicle is capable of vertical take-off and landing (VTOL). Due to its tilt-wing structure, it can also fly horizontally. The mathematical model of the vehicle is obtained using Newton-Euler formulation. A gravity compensated PID controller is designed for altitude control, and three PID controllers are designed for attitude stabilization of the vehicle. Performances of these controllers are found to be quite satisfactory as demonstrated by indoor and outdoor flight experiments