Unmanned Systems Technology 027 l Hummingbird XRP l Gimbals l UAVs insight l AUVSI report part 2 l O’Neill Power Systems NorEaster l Kratos Defense ATMA l Performance Monitoring l Kongsberg Maritime Sounder

50 causing the vehicle to lose altitude.” The autopilot typically responds by actuating the collective lever to increase the pitch angle, which only slows the main rotor more (since there is no power), until it stops entirely. Before this issue can be solved, the autopilot needs to be able to safely recognise and declare when an engine failure has occurred, in order to begin the autorotation manoeuvre. Necessary mechanical changes to the Alpha 800 system included integrating a one-way bearing and clutch on the main rotor transmission, to ensure the main rotor can continue to be driven by the main transmission, but without the reverse happening. That prevents the tail rotor being pulled during autorotation, thus keeping all the energy on the main rotor and reducing the vertical and horizontal movement speed required for gliding. Also, an rpm sensor has been directly coupled to the main rotor, to ensure a constant feed of rpm measurements to the autopilot. “Some UAV helicopters have their rpm sensors installed on the engine or some part of the transmission, which will not work during autorotation,” Escarpenter says. “The propeller blades must be designed with the capability to be set to a negative pitch as well, in order to increase the main rotor speed by pulling back on the collective lever when the UAV falls below the target revs.” The autopilot system from UAV Navigation has also been programmed with the necessary logical pathways to identify the conditions unique to an engine failure, and to control the mechanical aspects of autorotation that Alpha Unmanned had designed in. After 18 months of working with UAV Navigation, Alpha Unmanned Systems conducted flight testing of the autorotation technology at its airfield, with the aim of consistently gliding and landing safely with the engine stopped. That also required developing the capability to simulate an engine failure without repeatedly (or ever) putting the UAV at risk of being destroyed. The test programme consisted of more than 100 simulated autorotation manoeuvres with the engine at idle, with the flight team iteratively adding more complexity with each test as they collected and analysed the UAV’s telemetry and flight data. The Vector autopilot has also been gradually updated to improve its autorotation logics, and has had a number of protection features added to avoid saturating the engine or the collective lever (which reduced the possibility of a failure requiring autorotation in the first place). Oil and gas As the prospect of legal BVLOS commercial UAV flights becomes more and more likely, Robot Aviation has successfully conducted two BVLOS training flights with US company Skyskopes. The latter plans to use the former’s FX20 aircraft in aerial oil and gas infrastructure inspections. “Our training site allows us to fly BVLOS operations, which is important for us because in the US it’s very complicated to do that, with strict constraints on flight corridors and similar obstacles of that nature,” explains Niklas Nyroth, director at Robot Aviation. “The flights took place in the first week of December 2018, and Skyskopes has bought an FX20 system specifically to provide an aerial inspection capability for the oil and gas industry in North August/September 2019 | Unmanned Systems Technology Insight | UAVs Some helicopters have their rpm sensors installed on the engine or a part of the transmission, which won’t work in autorotation Autonomous autorotation on helicopter UAVs will greatly reduce the dangers posed by an engine failure or transmission breakdown (Courtesy of Alpha Unmanned Systems)