William J. Crowther

A demonstration of a fully onboard method for generating background oriented schlieren (BOS) data on a jet exhaust is presented. Readily available commercial camera equipment is used to capture in-flight imagery of a miniature jet engine exhaust mounted on a custom-built model aircraft. The setup for image acquisition and processing algorithms are described. A new process for registration of images to reduce the degrading effects of vibration and flexure of the airframe are developed and presented along with the underpinning BOS algorithm. Results show that jet flows can be visualised using this technique using a contained system on a single aircraft and demonstrate how a simple technique, such as BOS, can be democratised to such an extent that the cost of conducting in-flight jet measurements can be reduced to the budget of any model aircraft flyer.

Projections for future air mobility envisage intensely utilized airspace that does not simply scale up from existing systems with centralized air traffic control. This paper considers the implementation and test of a software and hardware framework for decentralized control of aerial vehicles within intensely used airspace. Up to 10 rotary wing vehicles of maximum all up mass of are flown in an outdoor volume with length scale of with GPS and WiFi connectivity. Flight control is implemented using a Pixhawk 4 flight controller running the PX4 firmware with guidance algorithms run on a separate onboard companion computer. Deconfliction is implemented using a simple elastic repulsion model with a guidance update rate of . Traffic structures are constructed from a path of directed waypoints and associated cross sectional geometry. Junctions are implemented when two paths converge into one or when one path diverges into two. Agents engage with structures through execution of flow, merge and swirl velocity rules. Calibration experiments showed that the worst case latency in agents sharing position information was of the order of made up from delays due to finite guidance update rate, WiFi processing and centralized message processing. A choice of vehicle cruise speed of and conflict radius of provided an acceptable compromise between experiment time efficiency (speed) and spatial efficiency (resolution) within the test volume. Results from recirculating junction experiments show that peak deconfliction activity occurs at the junction node, however biased distribution of agents within a corridor means the peak intensity is pushed ahead of the node. Use of meshed helical junction structures significantly reduces the intensity of conflict at the expense of reduced junction time efficiency.

A framework is presented for distributed control of rotary wing aerial robots using open-source flight controller firmware, commercial communication and computing hardware in an outdoor visual line of sight test environment. The work builds upon existing documented frameworks that focus mainly on laboratory based experiments. The research context is evaluation of novel rules for safe intersection of high-density aerial traffic flows. The framework is based on the use of a PX4 flight controller, Linux onboard computer running bespoke flight management code, MAVlink WiFi Bridge and WiFi module on each flight vehicle, and a ground control station running QGroundControl and a bespoke graphical user interface for interaction with vehicles and control of the overall experiment. SITL functionality is provided using Gazebo for physical simulation. Communication is via WiFi, with an individual radio control transmitter for each vehicle provided as backup. The developed framework was evaluated using a fleet of 10 multirotor vehicles based on 1kg class racing drones operating in a test volume approximately 100x100x100m. Engineering evaluation results are presented in the form of an technical issue register which highlights the engineering challenges that had to be solved to achieve a practical working system. Results are then presented for an example drone traffic intersection experiment in which two helical traffic flows are joined without conflict using flight rules running local to each drone. The proposed framework has been shown to be scalable to up to 10 vehicles, with addition of further vehicles being limited by WiFi router performance. The framework is hardware agnostic as far as possible and is extensible to use for a range of different distribute control experiments.

Tailless aircraft without vertical stabilisers typically use drag effectors in the form of spoilers or split flaps to generate control moments in yaw. This paper introduces a novel control allocation method by which full three-axis control authority can be achieved by the use of conventional lift effectors only, which reduces system complexity and control deflection required to achieve a given yawing moment. The proposed method is based on synthesis of control allocation modes that generate asymmetric profile and lift induced drag whilst maintaining the lift, pitching moment and rolling moment at the trim state. The method uses low order models for aerodynamic behaviour characterisation based on thin aerofoil theory, lifting surface methodology and ESDU datasheets and is applied to trapezoidal wings of varying sweep and taper. Control allocation modes are derived using the zero-sets of surrogate models for the characterised aerodynamic behaviours. Results are presented in the form of control allocations for a range of trimmed sideslip angles up to 10 degrees optimised for either maximum aerodynamic efficiency (minimum drag for a specific yawing moment) or minimum aggregate control deflection (as a surrogate observability metric). Outcomes for the two optimisation objectives are correlated in that minimum deflection solutions are always consistent with efficient ones. A configuration with conventional drag effector is used as a reference baseline. It is shown that, through appropriate allocation of lift based control effectors, a given yawing moment can be produced with up to a factor of eight less aggregate control deflection and up to 30% less overall drag compared to use of a conventional drag effector.

Offshore high voltage DC (HVDC) wind farms offer a promising solution to growing energy demands in the future. Condition monitoring of substation assets is essential for reliable and resilient operation of electrical networks. Existing condition monitoring techniques for onshore substation and electrical network assets include regular and scheduled on-site visits by trained personnel to substation sites. However, such routine inspection is not a cost-effective solution for offshore sites. In cases where the accessibility to network assets becomes difficult, robotic and autonomous condition monitoring provides a solution. Such a robotic/autonomous solution would need to interact with the surrounding substation environment, without increasing the risk of electrical breakdown and flashovers between different energized components. In Part A of this paper, the effect of high electrostatic fields on an inspection unmanned aerial vehicle (UAV) is analyzed, with respect to: 1) AC corona emissions interference on the UAV, and 2) Air breakdown clearance characteristics. Both simulations and experiment results presented in the paper show the impact of corona emissions interference to both UAV autopilot and actuation sections, which requires a shielding mitigation solution. Also, experiment results show the limited effect of introducing a shielding solution on increasing the flashover risk between valve hall towers.

For HVDC links, the substation is a major cost factor. 3D visualization using virtual reality has the potential to play a significant part in cost reduction. This paper outlines the problem and gives two examples: the use of visualization for planning internal drone inspection; and the application of visualization to the design of a superconducting fault-current limiter breaker.

Jumping take-off in birds is an explosive behaviour with the goal of providing a rapid transition from ground to airborne locomotion. An effective jump is predicated on the need to maintain dynamic stability through the acceleration phase. The present study concerns understanding how birds retain control of body attitude and trajectory during take-off. Cursory observation suggests that stability is achieved with relatively little cost. However, analysis of the problem shows that the stability margins during jumping are actually very small and that stability considerations play a significant role in the selection of appropriate jumping kinematics. We use theoretical models to understand stability in prehensile take-off (from a perch) and also in non-prehensile take-off (from the ground). The primary instability is tipping, defined as rotation of the centre of gravity about the ground contact point. Tipping occurs when the centre of pressure falls outside the functional foot. A contribution of the paper is the development of graphical tipping stability margins for both centre of gravity location and acceleration angle. We show that the nose-up angular acceleration extends stability bounds forward and is hence helpful in achieving shallow take-offs. The stability margins are used to interrogate simulated take-offs of real birds using published experimental kinematic data from a guinea fowl (ground take-off) and a diamond dove (perch take-off). For the guinea fowl, the initial part of the jump is stable; however, simulations exhibit a stuttering instability not observed experimentally that is probably due to the absence of compliance in the idealized joints. The diamond dove model confirms that the foot provides an active torque reaction during take-off, extending the range of stable jump angles by around 45°.