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SummaryPosition-tracking problems in the structures of rigid formations of nonholonomic mobile robots, such as fixed-wing unmanned aerial vehicle (UAVs), must reconcile tracking precision and flight stability, which usually exclude each other due to nonholonomic motion constraints. Therefore, a position-tracking control that is based on distance and position displacement, defined as inputs of control loops, requires the application of dead zones around target positions, which are the points of instability. For this reason, the control becomes sensitive to any external disturbance causing oscillations of control signals and so it becomes difficult to maintain a zero value of position displacement over a long time horizon. Thus, we propose an approach based on the adaptive mechanism of an asymmetrical local artificial potential field, which is defined by a local frame of reference whose origin is located in the tracked position of a UAV in the formation frame. It couples controls of both airspeed and heading angle into a nonlinear potential function of relative position and orientation with respect to the tracked position and adapts it according to heading rate of the leader. The function splits the area around the tracked position longitudinally into two zones of acceleration and deceleration; therefore, velocity vectors are longer (higher airspeed) only when a UAV is behind the tracked position and shorter (lower airspeed) when it is ahead. The area is laterally symmetrical, and orientations of velocity vectors align asymptotically to the longitudinal direction accordingly with the decrease in the lateral error. Finally, velocity vectors are rotated proportionally to the heading rate of the leader, which improves the tracking precision during turns. If we assumed that a UAV’s tracked position is in motion, it could easily be proven that the position control based on the adaptive asymmetrical potential function becomes asymptotically stable in the tracked position. Numerical simulation verifies this thesis and presents more precise and stable position tracking due to the adaptation mechanism.

This article presents research on a hybrid vertical take‐off and landing (VTOL) unmanned aerial vehicle (UAV) supported by a relative positioning system, enabling the deployment of autonomous missions from ship‐based helipads in maritime conditions. A crucial issue to be solved is ensuring precise positioning of the UAV relative to the landing pad in the take‐off and landing phases. To achieve this, an extended Kalman filter (EKF) is implemented on the UAV's onboard computer, which integrates the positioning data from the UAV's global navigation satellite system receiver and the positioning data of the landing pad broadcast by the landing pad navigation station (LNS). The EKF estimates both the absolute and relative position of the UAV, which are required for autonomous take‐off and landing on the moving landing pad. In unfavorable weather conditions, EKF also uses data from an optional local positioning system to keep the accuracy within the range 1–3 m. The research was concluded by experimental verification during a ferry cruise over the Baltic Sea. During the research, the VTOL UAV performed two fully autonomous flight missions at the range about 1 km from the moving ferry in international waters. Each of them ended with a successful landing back on the helipad with an accuracy matching its required level, which was already achieved in the previous research carried out in inland conditions. Data recorded during real flights confirm that the developed system, consisting of a hybrid VTOL UAV and a LNS, is ready to be utilized in autonomous missions at sea. Factors having a critical impact on the safety of use of the VTOL UAV in marine conditions were also identified, which were not observed during the research in inland conditions, and are related directly to turbulence around the landing pad.

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The problem of autonomous formation flight control of UAVs (Unmanned Aerial Vehicles) is presented in the paper. A decentralized control method of the autonomous formation flight realization is described. A practical approach to the UAV formation flight control was shown. The applied method bases on the information exchange between flying objects. The shared data concern the position and velocity of the aircraft. Constructed UAV airframe was presented as well as used autopilot, developed formation flight control unit, wireless communication links and used data packet structure. The main aim of this work was the in-flight tests. The test of formation flight with Virtual Leader (VL) was examined. The autopilot reactions to the incoming data packets with desired altitude, airspeed and heading from formation flight controller were checked. During the flights the longitudinal and lateral positions of the UAV, orientation angles (pitch, roll, yaw), angular velocities (pitch rate, roll rate, yaw rate) and many other flight parameters were logged. The research and flight tests checked and verified the developed method of formation flight control.

The paper presents a concept of a magnetic coil launcher for unmanned aerial vehicles of mass up to 25 kg. The idea is not new, nevertheless in the paper, an innovative application of magnetic launcher technology for selected class of unmanned aerial vehicles is presented. So far, at Bialystok University of Technology, a magnetic coil launcher for micro aerial vehicles of mass up to 2.5 kg has been investigated. In the article, simulations of a conceptual multi-coil launcher with a magnetic core system are presented. The finite element method has been used in calculations. Moreover, in the paper, the concept of a magnetic support for transmission of mechanical power from the magnetic core to the launched payload is proposed. The applied methodology, computational results and potential technical difficulties of practical applications are also widely discussed.