På SAAB AB pågår projekt vilka har till syfte att utveckla en obemannad flygfarkost (UAV) som komplement till vanliga flygplan, exempelvis Gripen. För att kunna göra detta behöver SAAB samla kunskaper om UAV:er i allmänhet och detta examensarbete är en del i denna process. Detta examensarbete har utförts hos SAAB AB, avdelningen Future Products i Linköping. Syftet var att ta fram styrlagar som möjliggör autonom landning för en UAV. Även en kortare utredning om vilka sensorer som kan komma att behövas ingick i examensarbetet. Slutsatserna visar att ytterligare förbättringar behövs innan en autonom landning kan genomföras med den algoritm som tagits fram inom ramen för detta examensarbete. Bland annat behöver man ta hänsyn till turbulens. Vad gäller val av sensorer kan man i början använda sig av standard produkter som är kommersiellt tillgängliga för att reducera kostnaderna i projektet. / At SAAB AB there are projects running whose purpose is to develop an Unmanned Aerial Vehicle (UAV) to be used as a complement to ordinary aircrafts like Gripen. In order to do this SAAB has to collect generic knowledge about UAV:s and this final thesis is a part of this process. This final thesis has been performed at SAAB AB in the department for Future Products in Linköping. The purpose was to develop control algorithms which makes autonomous landing possible for UAV:s. A brief investigation about which sensors that may have to be used was also performed as a part of the final thesis. The conclusions show that further improvements are needed before an autonomous landing can be carried out with the algorithm that was developed within the scope of this thesis. Among other things, turbulence must be taken into consideration. Regarding the sensors, it is possible to start out with commercial of the shelf (COTS) products in order to decrease costs in the project.

The use of Unmanned Aerial Vehicles (UAVs) has rapidly increased over the last years. This has been possible mainly due to the increased computing power of microcontrollers and computers. An UAV can be used in both civilian and military areas, for example surveillance and intelligence. The UAV concerned in this master's thesis is a prototype and is currently being developed at DST Control AB in Linköping. With the use of UAVs, the need for a positioning and navigation system arises. Inertial sensors can often give a good position estimation, however, they need continuous calibration due to error build-up and drift in gyros. An external reference is needed to correct for this drift and other errors. The positioning system investigated in this master's thesis is supposed to work in an area defined by an inverted cone with the height of 25m and a diameter of 10m. A comparison of different techniques suitable for position sensing has been performed. These techniques include the following: a radio method based on the Instrument Landing System (ILS), an optical method using a Position Sensing Detector (PSD), an optical method using the Indoor GPS system, a distance measurement method with ultrasound and also a discussion of the Global Positioning System (GPS). An evaluation system has been built using the PSD sensor and tests have been performed to evaluate its possibilities for positioning. Accuracy in the order of a few millimetres has been achieved in position estimation with the evaluation system.

I en obemannad flygfarkost måste datorer ta över pilotens förmåga att värdera risker och undvika kollisioner. På algoritmnivå brukar man dela in problemet i tre delar: Upptäckt och estimering av inblandade farkosters positioner och hastigheter, kollisionsriskberäkning och slutligen undanmanöver. Saabs arbete med obemannade farkoster har tidigare berört kollisionsundvikning lite ytligt men nu börjat på större allvar. Det här examensarbetet är en del i denna satsning och har resulterat i ett sätt att beräkna kollisionsrisken samt ett sätt att beräkna en undanmanöver, givet att de inblandade farkosternas positioner och hastigheter är kända. I examensarbetet behandlas parvisa kollisionsscenarier mellan ickekommunicerande farkoster givet två olika fall. Dels där den främmande farkostens position skattats väl, dels där den främmande farkostens position skattats sämre. En enkel simuleringsmiljö har utvecklats, där två algoritmer för beräknandet av kollisionsrisken, en för varje fall, testats samtidigt som undanmanövern testats för en mängd kollisionsscenarier. Givet att den främmande farkostens position skattats väl behöver den obemannade farkosten cirka 6 s på sig för att kunna undvika en kollision. I fallet där den främmande farkostens position skattats sämre kan vi beräkna kollisionsrisken och i vissa fall sluta oss till hur farkosterna är orienterade och därigenom göra ett undanmanöverval. / Saabs work with unmanned aerial vehicles has only scratched the surface of collision avoidance, but is now advancing. This master thesis sheds light on some parts of the collision avoidance problem and has resulted in an innovative way to calculate the risk of collision and a way to determine an avoidance maneuver. In this master thesis collision scenarios between non-communicating vehicles are being looked upon in pairs, given two different sets of data. Good estimates of the unknown vehicles position and unsatisfying position estimate. Through the development of a simple simulation environment, two algorithms, one for each set of data, has been tested simultaneously with tests of the collision avoidance maneuver for several collision scenarios. Given a good estimate of the unknown aerial vehicles position, the unmanned vehicle need approximately 6 seconds to act to avoid a collision. For the case with unsatisfactory estimate of the unknown vehicle the risk of collision can be calculated and in some cases the orientation of the aerial vehicles and thus a choice of avoidance maneuver can be made.

Recent advances in sensor and microcomputer technology and in control and aeroydynamics theories has made small unmanned aerial vehicles a reality. The small size, low cost and manoueverbility of these systems has positioned them to be potential solutions in a large class of applications. However, the small size of these vehicles pose significant challenges. The small sensors used on these systems are much noisier than their larger counterparts.The compact structure of these vehicles also makes them more vulnerable to environmental effects. This work develops several different control strategies for two sUAV platforms and provides the rationale for judging each of the controllers based on a derivation of the dynamics, simulation studies and experimental results where possible. First, the coaxial helicopter platform is considered. This sUAV’s dual rotor system (along with its stabilizer bar technology) provides the ideal platform for safe, stable flight in a compact form factor. However, the inherent stability of the vehicle is achieved at the cost of weaker control authority and therefore an inability to achieve aggressive trajectories especially when faced with heavy wind disturbances. Three different linear control strategies are derived for this platform. PID, LQR and H∞ methods are tested in simulation studies. While the PID method is simple and intuitive, the LQR method is better at handling the decoupling required in the system. However the frequency domain design of the H∞ control method is better at suppressing disturbances and tracking more aggressive trajectories. The dynamics of the quadrotor are much faster than those of the coaxial helicopter. In the quadrotor, four independent fixed pitch rotors provide the required thrust. Differences between each of the rotors creates moments in the roll, pitch and yaw directions. This system greatly simplifies the mechanical complexity of the UAV, making quadrotors cheaper to maintain and more accessible. The quadrotor dynamics are derived in this work. Due to the lack of any mechanical stabilization system, these quadrotor dynamics are not inherently damped around hover. As such, the focus of the controller development is on using nonlinear techniques. Linear quadratic regulation methods are derived and shown to be inadequate when used in zones moderately outside hover. Within nonlinear methods, feedback linearization techniques are developed for the quadrotor using an inner/outer loop decoupling structure that avoids more complex variants of the feedback linearization methodology. Most nonlinear control methods (including feedback linearization) assume perfect knowledge of vehicle parameters. In this regard, simulation studies show that when this assumption is violated the results of the flight significantly deteriorate for quadrotors flying using the feedback linearization method. With this in mind, an adaptation law is devised around the nonlinear control method that actively modifies the plant parameters in an effort to drive tracking errors to zero. In simple cases with sufficiently rich trajectory requirements the parameters are able to adapt to the correct values (as verified by simulation studies). It can also adapt to changing parameters in flight to ensure that vehicle stability and controller performance is not compromised. However, the direct adaptive control method devised in this work has the added benefit of being able to modify plant parameters to suppress the effects of external disturbances as well. This is clearly shown when wind disturbances are applied to the quadrotor simulations. Finally, the nonlinear quadrotor controllers devised above are tested on a custom built quadrotor and autopilot platform. While the custom quadrotor is able to fly using the standard control methods, the specific controllers devised here are tested on a test bench that constrains the movement of the vehicle. The results of the tests show that the controller is able to sufficiently change the necessary parameter to ensure effective tracking in the presence of unmodelled disturbances and measurement error.

Active flow control has been extensively explored in wind tunnel studies but successful in-flight implementation of an active flow control technology still remains a challenge. This thesis presents implementation of active flow control technology onboard a 33% scale Extra 330S ARF aircraft, wind tunnel studies and flight testing of fluidic actuators. The design and construction of the pulsed blowing system for stall suppression (LE actuator) and continuous blowing system for roll control (TE actuator) and pitch control have been presented. Full scale wind tunnel testing in 7̕ X 10 Oran W. Nicks low speed wind tunnel shows that the TE actuators are about 50% effective as the conventional ailerons. The LE actuator is found to be capable of suppressing stall from 12° to about 22°. Comparison of characteristics of Active elevator and conventional elevator in 3' X 4' low speed wind tunnel show that, the active elevator is as effective as of conventional elevator deflected at 5°. Flight tests show that TE actuators are able to control the aircraft in flight in banked turns. The measured roll rates in-flight support the wind tunnel test findings.

This thesis work deals with manufacturing a lightweight composite unmanned aerial vehicle (UAV) wing, material characterization of the composites used in the UAV wing, and preliminary structural analysis of the UAV wing. Manufacturing is performed at the composite laboratory founded in the Department of Aerospace Engineering, and with hand lay-up and vacuum bagging method at room temperature the wing is produced. This study encloses the detailed manufacturing process of the UAV wing from the mold manufacturing up to the final wing configuration supported with sketches and pictures. Structural analysis of the composite wing performed in this study is based on the material properties determined by coupon tests and micromechanics approaches. Contrary to the metallic materials, the actual material properties of composites are generally not available in the material handbooks, because the elastic properties of composite materials are dependent on the manufacturing process. In this study, the mechanical properties, i.e. Young&rsquo / s Modulus, are determined utilizing three different methods. Firstly, longitudinal tensile testing of the coupon specimens is performed to obtain the elastic properties. Secondly, mechanics of materials approach is used to determine the elastic properties. Additionally, an approximate method, that can be used in a preliminary study, is employed. The elastic properties determined by the tests and other approaches are compared to each other. One of the aims of this study is to establish an equivalent material model based on test and micromechanics approach, and use the equivalent model in the structural analysis by finite element method. To achieve this, composite structure of the wing is modeled in detail with full composite material descriptions of the surfaces of the wing structure, and comparisons are made with the results obtained by utilizing equivalent elastic constants. The analyses revealed that all three approaches have consistent, and close results / especially in terms of deflections and natural frequencies. Stress values obtained are also comparable as well. For a case study on level flight conditions, spanwise wing loading distribution is obtained using a program of ESDU, and the wing is analyzed with the distributed loading. Reasonable results are obtained, and the results compared with the tip loading case. Another issue dealt in this study is analyzing the front spar of the wing separately. The analysis of the front spar is performed using transformed section method and finite element analysis. In the results, it is found that both methods calculates the deflections very close to each other. Close stress results are found when solid elements are used in the finite element analysis, whereas, the results were deviating when shell elements are used in the analysis.

This thesis concerns with the design and development of automatic flight controller strategies for the autonomous landing of fixed wing unmanned aircraft subject to severe environmental conditions. The Tactical Unmanned Aerial Vehicle (TUAV) designed at the Middle East Technical University (METU) is used as the subject platform. In the first part of this thesis, a dynamic model of the TUAV is developed in FORTRAN environment. The dynamic model is used to establish the stability characteristics of the TUAV. The simulation model also incorporates ground reaction and atmospheric models. Based on this model, the landing trajectory that provides shortest landing distance and smallest approach time is determined. Then, an automatic flight control system is designed for the autonomous landing of the TUAV. The controller uses a model inversion approach based on the dynamic model characteristics. Feed forward and mixing terms are added to increase performance of the autopilot. Landing strategies are developed under adverse atmospheric conditions and performance of three different classical controllers are compared. Finally, simulation results are presented to demonstrate the effectiveness of the design. Simulation cases include landing under crosswind, head wind, tail wind, wind shear and turbulence.

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 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.

This thesis investigates the effects of camber change on the mission adaptive wing of a structurally designed unmanned aerial vehicle (UAV). The commercial computational fluid dynamics (CFD) software ANSYS/FLUENT is employed for the aerodynamic analyses. Several cambered airfoils are compared in terms of their aerodynamic coefficients and the effects of the camber change formed in specific sections of the wing on the spanwise pressure distribution are investigated. The mission adaptive wing is modeled structurally to observe the effect of spanwise pressure distribution on the wing structure. For the structural design and analysis of the UAV under this study, commercial software MSC/PATRAN and MSC/NASTRAN are used. The structural static and dynamic analyses of the unmanned aerial vehicle are also performed under specified flight conditions. The results of these analyses show that the designed structure is safe within the flight envelope. Having completed aero-structural design and analysis, the designed unmanned aerial vehicle is manufactured by TUSAS Aerospace Industries (TAI).