In this thesis aeroelastic analysis of a typical Unmanned Aerial Vehicle (UAV) using MSC&reg / FlightLoads and Dynamics module and MSC&reg / NASTRAN Aero 1 solver was performed. The analyses were carried out at sea level, 1000m, 2000m and 4000m altitudes for Mach Numbers M=0.2, 0.4 and 0.6 for the full model of the UAV. The flutter characteristics of the UAV for different flight conditions were obtained and presented. The effect of altitude on flutter characteristics has been examined and compared with the theoretical and experimental trends in the literature. Also the divergence characteristics of the full model UAV was obtained. In the study, some verification and test cases are also included. The results of the analyses of an untapered swept-wing and AGARD 445.6 wing models were compared with wind tunnel data and a maximum error of 1.3 % in the flutter speed prediction was obtained. In two different wing models the effect of taper was investigated.

In this study structural design, analysis and composite manufacturing applications for a tactical UAV, which was designed and manufactured in Aerospace Engineering Department of Middle East Technical University (METU), is introduced. In order to make an accurate structural analysis, the material and loading is modeled properly. Computational fluid dynamics (CFD) was used to determine the 3D pressure distribution around the wing and then the nodal forces were exported into the finite element program by means of interpolation from CFD mesh to finite element mesh. Composite materials which are mainly used in METU TUAV are woven fabrics which are wetted with epoxy resin during manufacturing. In order to find the elastic constants of the woven fabric composites, a FORTRAN code is written which utilizes point-wise lamination theory. After the aerodynamic load calculation and material characterization steps, linear static and dynamic analysis of the METU TUAV&rsquo / s wing is performed and approximate torsional divergence speed is calculated based on a simplified approach. Lastly, co-cured composite manufacturing of a multi-cell box structure is explained and a co-cured multi-cell box beam is manufactured.

In this thesis the development of a nonlinear simulation model of a utility helicopter and the design of its automatic flight control system is addressed. In the first part of this thesis, the nonlinear dynamic model for a full size helicopter is developed using the MATLAB/SIMULINK environment. The main rotor (composed of inflow and flapping dynamics parts), tail rotor, fuselage, vertical stabilizer, horizontal stabilizer of the helicopter are modeled in order to obtain the total forces and moments needed for the flight simulation of the helicopter. Total forces and moments are used in 6 degrees of freedom equations of motion model and helicopter states are calculated for the specified flight conditions such as hover and forward flight. Trim and linearization programs are developed. The linearized models of hover and forward flight conditions are used for the automatic flight control system design. Automatic flight control system model consists of necessary systems in order to ease the pilot control of the helicopter. A classical inner stability loop and outer flight directory mode approach is taken to design the automatic flight control system. For the inner stability loop both classical rate feedback and truncated system state feedback control approaches are used. The outer loop modes implemented are heading hold, attitude hold (pitch, roll), altitude acquire and hold mode for hover condition and heading hold, attitude hold (pitch, roll), altitude acquire and hold mode and airspeed hold for forward flight condition. Finally, the success of the controllers are demonstrated through nonlinear simulations for different flight directory modes in hover and forward flight conditions.

Modeling the ionosphere, where the effects of solar dynamo becomes more effective to space based and ground borne activities, has an undeniable importance for telecommunication and navigation purposes. Mid-latitude electron density trough is an interesting phenomenon in characterizing the behavior of the ionosphere, especially during disturbed conditions. Modeling the mid-latitude electron density trough is a very popular research subject which has been studied by several researchers until now. In this work, an operational technique has been developed for a probabilistic space weather forecast using fuzzy modeling and computer based detection of trough in two steps. First step is to detect the appropriate geomagnetical conditions for trough formation, depending on the values of 3-h planetary K index (Kp), magnetic season, latitude and local time, by using fuzzy modeling technique. Once the suitable geomagnetic conditions are detected, second step is to find the lower latitude position (LLP) and minimum position (MP) of the observed trough being two main identifiers of the mid-latitude electron density trough. A number of case studies were performed on ARIEL 4 satellite data, composed of different geomagnetic, annual and diurnal characteristics. The results obtained from fuzzy modeling show that the model is able to detect the appropriate conditions for trough occurrence and the trough shape was effectively identified for each selected case by using the predefined descriptions of mid-latitude electron density trough. The overall results are observed to be promising.

This study describes the design and implementation of the pitch and roll autopilots for a fixed wing unmanned vehicle. A Tactical Unmanned Aerial Vehicle (TUAV), which is designed at the Middle East Technical University (METU), is used as a platform. This work combines development of the classical and robust controllers, which are used for the pitch and roll autopilots. One of the important steps in the thesis is development of the non-linear dynamic model of the UAV, which is developed in MATLAB/Simulink environment. Two different strategies of the controller design imply development of the PID and controllers. Simulation results illustrate the performances of the designed controllers. Simulation is performed for the nominal model of the UAV and for the model that includes uncertainties and sensor noises.

In this study, equipment rack structure for a medium transport aircraft was designed and finite element analysis of this design was performed. The equipment rack structure, which was designed for a modernization project, was positioned and dimensions were determined by regarding the geometry of primary structures of the aircraft. The structure was designed such that it satisfies the pre-defined margin of safety values. Design of the structure was prepared in Unigraphics, and the finite element modeling and analysis phases were carried out using MSC.Patran and MSC.Nastran programs. For the fastener analysis, which is usually carried out by hand calculations, two analysis tools were prepared by using FORTRAN and Microsoft Office Excel programs. These tools were found to greatly facilitate the analysis and save time. As these tools can be used in other finite element analyses, in which MSC.Patran and MSC.Nastran programs are used, user manuals were prepared.

This thesis investigates the flow field of a twin-engine, medium lift utility helicopter numerically. The effects of the exhaust hot gases emerging from the engines are accounted for in the numerical study. The commercial computational fluid dynamics (CFD) software ANSYS Fluent is employed for the computations. While the effects of engines are included in the computations through simple inlet and outlet boundary conditions, the main and tail rotors are simulated by the Virtual Blade Model in a time-averaged fashion. Forward flight at four different advance ratios and hover in ground effect are studied. The temperature distribution around the tail boom is compared to available flight test data. Good agreement with the flight test data is observed.

In the thesis, automatic flight control system is designed for Tilt Duct Unmanned Aerial Vehicle (UAV). The vehicle is a Vertical Take-Off Landing (VTOL) type with two symmetric rotors on the wings, one aft rotor on the aft body. It behaves like a helicopter but with higher speeds in forward flight. Transition flight of the aircraft from hover to cruise or take-off to forward flight is the primary concern of the thesis study with the nonlinearities and instabilities encountered, together with the over-actuated controls in this mode. A nonlinear simulation code is developed including nonlinear equations of motion together with the nonlinear aerodynamics, environmental eects, and rotor dynamics. Trim and linearization codes are also developed. Trim conditions for the transition flight phase are calculated for two different transition scenarios. Linear controllers are developed and nonlinear controller is designed for the transition mode. Nonlinear controller uses the state dependent Ricatti equation SDRE approach by using extended linearization. Two loop approach is used in order to increase controllability. In the inner loop, attitude rates are fed back and SDRE approach is used to calculate the feedback gain matrix online. In the outer loop, vehicle attitude is controlled using the eigenvalue assignment. Blended inverse algorithm based control allocation method is used in control of the over-actuated transition phase. This algorithm is shown to be quite effective among different methods in not only generating necessary forces needed for the control, but also allocating with more control authority on the desired actuator.

ABSTRACT EXPERIMENTAL AND NUMERICAL INVESTIGATION OF FLOW FIELD AROUND FLAPPI G AIRFOILS MAKING FIGURE-OF-EIGHT IN HOVER BASKAN, &Ouml / zge M.Sc., Department of Aerospace Engineering Supervisor: Prof. Dr. H. Nafiz Alemdaroglu September 2009, 94 pages The aim of this study is to investigate the flow field around a flapping airfoil making figure-of-eight motion in hover and to compare these results with those of linear flapping motion. Aerodynamic characteristics of these two-dimensional flapping motions are analyzed in incompressible, laminar flow at very low Reynolds numbers regime using both the numerical (Computational Fluid Dynamics, CFD) and the experimental (Particle Image Velocimetry, PIV) tools. Numerical analyses are performed to investigate the effect of different parameters such as the amplitude of motion in y-direction, angle of attack, Reynolds number and camber on the aerodynamic force coefficients and vortex formation mechanisms. Both symmetric and cambered airfoil sections are investigated at three different starting angles of attack for five different amplitudes of motion in y-direction including linear flapping motion. Experimental simulations are performed in order to verify the numerical results only for linear motion at Reynolds number of 1000 for symmetric and cambered airfoils at three different angles of attack. Computed vortical structures are then compared to vorticity contours obtained from the experiments and advantages of figure-of&ndash / eight motion over linear motion are discussed.

This thesis focuses on developing and examining the capabilities of a new in-house aerodynamic analysis tool, AeroSIM+, and investigating rotor-rotor aerodynamic interactions for two helicopters, one behind the other in forward flight. AeroSIM+ is a 3-D unsteady vortex panel method potential flow solver based on a free vortex wake methodology. Validation of the results with the experimental data is performed using the Caradonna-Tung hovering rotor test case. AeroSIM+ code is improved for forward flight conditions so that, the blades are allowed to move according to the rotor dynamics. In the simulations, blade airload prediction is seen to be sensitive to changes in vortex core size. Blade Vortex Interaction (BVI) locations differ depending on the relative position of the rear rotor with respect to the front rotor as well as on the forward flight speed. It was observed that the performance characteristics of the rear rotor alter depending on the relative positions of the rotors within the asymmetric wake flow field. The results of this thesis study such as the computed forces and moments on each rotor and the frequency characteristics of these loads can be also used in helicopter dynamics simulators.