Unmanned Systems Technology 033 l SubSeaSail Gen6 USSV l Servo actuators focus l UAVs insight l Farnborough 2020 update l Transforma XDBOT l Strange Development REVolution l Radio telemetry focus

88 Focus | Radio telemetry used with a 60 GHz radio and digital processor to achieve a 1.5 km link without having to use a dish antenna. With a 390 mm dish with 44 dBi gain, a complete system can achieve a 5 km link with a data rate of 1 Gbit/s. Urban environments Computational fluid dynamics (CFD) is used in the design of UAV platforms, but for the flight profile and flight envelope the presumption for most of the design is that the aircraft is flying in clean air. An urban environment doesn’t have that, so the industry has had to add gust responses for example as part of the certification, and there are standard gusts defined with a mathematical description. CFD analysis shows that a fixed-wing platform is more susceptible to gusts than a rotary craft, as there is more wing loading. CFD can also be used to model the environment around an unmanned aircraft in real time, which is especially useful in urban areas. This can be used to allow a UAV to avoid hazardous airflow features such as vortices to keep both the aircraft and any people on the ground safe. That is important, as the urban environment is likely to see a range of different craft being used, from autonomous air taxis in take-off/landing modes, to logistics delivery aircraft and surveillance UAVs. This closes the loop of the CFD design process of the platform, to quantify the areas in a city where they can safely operate. CFD is already used to create a double-precision floating-point simulation of the airflow in a built environment, for example to model the airflow through a city from a scale of kilometres down to metres. However, the data set is exceedingly large, too large to broadcast to a vehicle. So engineers are looking at how that data can be sent to a UAV effectively. There are a number of issues, mostly around the size of the platform. Larger platforms for example have more storage for the data, and are less susceptible to gusts. In smaller craft the payload is more crucial, so there is less storage and more susceptibility to changes in the airflow. This data can be communicated to a platform as command & control instructions to widely available autopilots. These have clearly defined interfaces to the control systems, and understand how to avoid obstacles so long as the aerodynamic hazard can be represented as an obstacle to avoid. This approach takes advantage of the existing infrastructure so that craft can avoid problem areas by imposing a no- fly zone rather than having the autopilot compensate in real time for changes in the airflow. That means there will be a dynamic data set, but the unanswered question at the moment is which data should be used to specify the size and position of a hazardous air feature as an object. The data is site-specific. Some airflow features are periodic, such as a vortex in a vertical cylinder created by buildings. Then there are asymmetric vortices for example, when wind is flowing past power lines, setting up vortices with a particular frequency. This is already a key issue for UAVs used to monitor such power lines. Whether there is similar periodic dynamism at a site determines how much the data can be compressed for the telemetry link. There are different types of data at different levels. For example, the CFD model in double precision for a city block would be Terabytes of data. Modelling this to specify the surfaces of the threat compresses that down to hundreds of kilobytes. Using simplified geometric primitives that approximate the surfaces reduces this further, to kilobytes of data. However, the amount of dynamic August/September 2020 | Unmanned Systems Technology Telemetry data can include simulations from CFD for safer operation of UAVs in urban areas (Courtesy of Zenotech) Urban settings don’t have clean air, so gust responses have had to be added to CFD analysis, and there are standard gusts