Issue 41 Unmanned Systems Technology December/January 2022 PteroDynamics X-P4 l Sense & avoid l 4Front Robotics Cricket l Autonomous transport l NWFC-1500 fuel cell l DroneX report l OceanScout I Composites I DSEI 2021 report

24 Dossier | PteroDynamics X-P4 System architecture Numerous key technologies have been combined in the X-P4, with three patents already granted and five more pending that formalise and globally protect PteroDynamics’ subsystem designs. As Graczyk explains, “A lot of big UAV companies have dozens of patents, but they are on individual components, like perhaps the method and design of lowering packages from a hovering aircraft. Our principal patent family covers the entirety of the Transwing aircraft design, including the articulating wings, the design of the propulsors on the wing, and how the wings rotate with a symmetrical dihedral.” While the company takes a modular approach to its aircraft designs, anticipating that different use-cases will require different airframes, aerofoils and tailplanes, a few key features currently stand out. These include a high aspect ratio wing and a vee tail with a largely composite hull. In addition to the 4 m wingspan, the fuselage measures about 2 m long. 2.2 kWh of energy is stored in COTS lithium-ion batteries that sit in the four wing-mounted propulsor nacelles, along with the electric motors and ESCs, and a CAN bus running data between the nacelles and the fuselage-mounted autopilot. Lightweight COTS wiring harnesses with locking connectors run between these systems, although the company’s roadmap includes r&d into optimising cables and plugs for sealing and EMI shielding. “At no turn have we opted for any exotic parts in this vehicle,” says Whitehand. “We use traditional, well- proven materials, design methods and COTS components. System integration, controls development and automation are where we see the most opportunity for innovation. “Keeping the powertrain in the wings may seem unusual but it yields great inertial relief, air cooling and a simplified structure, because the back tips of the nacelles act as landing struts.” Whitehand notes that the four electric motors together can deliver up to 10 times the necessary power for cruise. So, while all four are used in VTOL, with a peak climb rate of 1000 ft/minute and more, the X-P4 will typically shut off two motors during cruise, with their propellers passively folding back (pushed by airflow) and sitting tightly against the aerodynamic profile of the nacelles to lower power consumption and drag. “The high available power means we could fly comfortably at altitudes above 10,000 ft, but we’ve not tested that out,” he adds. “As interesting as it would be for us to find out, it’s not exactly a priority for customers.” Several hundred test cycles of sub- components have been performed, with final qualification testing for the US Navy planned for 2022. The Transwing In a Transwing aircraft, each wing attaches to the fuselage via a rotary hinge – each hinge is set at an angle – with an actuation system for deploying and stowing them. While each hinge sits on a winglet-like protrusion on either side of the forward fuselage, the actuator (a linear worm- December/January 2022 | Unmanned Systems Technology To transition between cruise and VTOL, a linear actuator moves a clip with two pushrods up and down the centreline of the UAV