This paper presents the design, flight mechanics and flight demonstration studies of a novel tiltable propeller VTOL UAV. The aircraft, discussed in this study, consists of a forwardswept fixed wing, two pairs of counter rotating tiltable propellers placed on both wing tips and a pair of counter rotating propeller placed between the tail booms. The aircraft has a capability of vertical take-off and landing as well as conventional take-off and landing. Both wing tip counter rotating propellers have been designed with a capability of tilting about ninety degrees around y-axis of the aircraft. The early design studies and the and the unexpected experimental results about ducted propeller systems have been summarized. The weight estimation approach has been discussed and initial sizes of the aircraft have been tabulated. After describing the general equation of motion, the trim condition calculations have been derived for hover, transition and cruise flight modes. The longitudinal stability characteristics for hover, transition and cruise flights have been analyzed via state space representation. The control strategies for all three flight modes have been evaluated and a control algorithm has been prepared. The construction studies of the test frames and the prototype aircraft have been summarized. Several flight demonstrations have been performed and the obtained results have been compared with the design calculations. Nomenclature VTOL = vertical take-off and landing CTOL = conventional take-off and landing EoM = equations of motion = mass cg = center of gravity = distance from cg to neutral point , , Z = components of resultant external force acting on aircraft , , = components of resultant external moment acting on aircraft , , = scalar components of velocity vector in body axis , , = scalar components of angular velocity vector in body axis , , = Euler angles , , = moments of inertia about (x, y, z) , , = products of inertia, (with respect to subscript) x, y, z = body frame axes, positive x forward of AC, positive y right wing (arm), positive z downward direction RPM = revolution per minute PWM = pulse width modulation MCU = micro-controller unit IMU = inertial measurement unit 0 = gross weight = empty weight = crew weight 2 = payload weight = fuel weight = propulsion system weight = structural weight = cruise velocity = stall velocity C k m = aerodynamic derivative coefficient of parameter k wrt parameter m , = main and aft duct tilt angles , = main and aft duct thrust values , = main and aft duct max thrust values Tn = thrust ratio of duct n e = elevator deflection α, β = angle of attack and side slip angle, resp. h = horizontal stabilizer incidence angle

The aim of this paper is to present the ongoing studies about design and fight testing of a fixed wing UAV which is able to take-off and land vertically. The UAV concept discussed in this study has three propeller engines. Two of them are ducted propellers and placed at each wing tips. The third engine is placed on the tail boom. The ducted propellers can rotate up to ninety degrees around the wing axis. The aircraft, which is planned to be built at the end of this study, will be able to take-off vertically, perform transition to conventional flight and land vertically. The aircraft will also have capability of conventional take-off, cruise flight and landing. In this study, the design considerations of the aircraft in terms of balance and stability ha been examined. The equations of motion of the aircraft have been modelled with nonlinear approach, and the hover and transition flight attitudes have been simulated via numerical calculations. It has been showed that the aircraft has an inherent unstable behavior during hover flight. Implementation of a Proportional and Integral (PI) control methodology in to the simulation provided artificial stability for both longitudinal and lateral motions. The transition flight equations have also been modelled and solved for open loop and closed loop control approaches. The rear motor thrust variations during tilting for both control approaches have been compared. A control algorithm which is implemented into a microcontroller onboard, has been developed for experimental studies. An indoor and an outdoor low cost test frames have been constructed. A single-closed loop and nested (cascade) closed loop control strategies have been applied to the test frames and artificial stability is achievedduring hover flight experimentally. The simulation results of hover and transition flights are presented in this article. The current status and results of the hover flight experiments are also summarized. The transition and cruise flight studies are planned as future work. Nomenclature AC = aircraft VTOL = vertical take-off and landing EOM = equation of motion = mass cg = center of gravity np = neutral point , , Z = components of resultant external force acting on aircraft , , = components of resultant external moment acting on aircraft , , = scalar components of velocity vector in body axis , , = scalar components of angular velocity vector in body axis , , = Euler angles , ,

The purpose of this work is to present a study on the stability and control of an unmanned, fixed wing, vertical take-off and landing aerial vehicle. This airplane is driven by a fixed-pitch tilt-propeller system with the capability of vertical take-off and landing as well as conventional flight. The novelty of the vehicle is the use of a fixed-pitch propeller system instead of variable-pitch tilt-rotors. There are three flight modes: vertical, transitional and conventional flight modes. Each flight mode has different dynamic characteristics. Therefore, these modes each need dedicated flight control methods. In this paper, the equations of motion are generated by modelling the aerodynamic and propulsion forces and moments. After performing trim condition calculations, longitudinal stability characteristics are investigated for each flight mode. The control methods are described for vertical, transitional and conventional flight modes. Stability augmentation systems, which consist of proportional and proportional/integral controller, are applied. A number of flight tests, including vertical, transitional and conventional flights, have been successfully performed with a prototype aircraft.

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