72 Insight | UAVs executed 5 days of continuous flight with the crewed version. Test data from that is informing the design, architecture and subsystem parameters needed for the uncrewed version, along with charging its batteries with solar energy during the day and running on stored energy at night. As part of the iterative process, Skydweller has replaced the Solar Impulse 2’s CS-23 push rod and cable control system with a fully redundant flyby-wire system using mechanically dual redundant servos – specifically the DA58HT from Volz (HT meaning high torque, although it is now named the DA-58D, for duplex). In addition to providing redundancy and hence long life and reliability for Skydweller’s flight durations, it also generated more torque than the solar powered aircraft needed, and significant data on the component for its supplier. “In fact, by using our COTS firmware in their crewed test flights, Skydweller were able to identify failure modes that we had never been able to address through our uncrewed aircraft customers,” says Mark Juhrig, CTO at Volz Servos. “They performed various tests in the air, and through those we were able to add a number of features to increase the safety of our servos that didn’t exist before. For instance, inside the servos we added a comms link between the two control lanes, so that they can supervise each other – one is designated the ‘slave’ lane, which can take over only when it has confirmed the ‘master’ lane is really dead.” The servos have now received authorisation from the EASA to be used in fly-by-wire trials of Skydweller’s test aircraft. Summary As UAVs such as those discussed above rack up more and more hours in extreme environments including the stratosphere, ocean storms, congested urban airspaces and disaster sites, the likelihood increases that more unpiloted aircraft will succumb to the hazards they present. It could be suggested here that the absence of a human pilot is a major problem for uncrewed attempts at such fights, with a pilot’s instincts being key to navigating dangerous turbulence and other factors. However, the advances being made by AI stand to make a huge difference in this regard. As companies increasingly fly beyond the edges of safe airspace, autopilot recordings of inertial, air pressure and GNSS data could be used to train flight algorithms to recognise and escape from unusual or highly dynamic flight conditions. With more time and maturing of such technology, algorithms could even be enhanced to safely compensate for those conditions. Without passengers on board, it hardly matters if strong g-forces or sickness-inducing manoeuvres are undertaken, so long as the aircraft’s controls can handle them. Before any of that happens though, AI is likely be used in predictive maintenance applications to better understand how critical components such as electric motors, propellers and servos degrade over time in unusual turbulence, or how batteries or pistons tolerate extremes of air pressure, frost or heat for example. In addition to experimenting with new ways to train AI and optimise other components, companies experimenting at the new frontiers of uncrewed operations will probably be faced with demand from other sectors interested in simulations of the dangerous mission environments they have taken on. As a result, while they might serve niche markets for now, major sectors such as commercial aviation and air freight will doubtless watch the progress of these UAVs with increasing interest. August/September 2023 | Uncrewed Systems Technology Volz’s DA-58HD servos have received authorisation from the EASA to be used in fly-by-wire trials of Skydweller’s stratospheric test aircraft (Courtesy of Skydweller Aero) By using our COTS firmware in their crewed test flights, Skydweller were able to identify failure modes we had never been able to address before
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