Uncrewed Systems Technology 047 l Aergility ATLIS l AI focus l Clevon 1 UGV l Geospatial insight l Intergeo 2022 report l AUSA 2022 report I Infinity fuel cell l BeeX A.IKANBILIS l Propellers focus I Phoenix Wings Orca

32 Flight control Transmissions between the flight control surfaces – the six e-motors as well as an elevator and rudder at the tail – are relayed over CAN bus at a rate of about 500 kbit/s. Although the MAT’s processes sound complex, the actual amount of data needed for control is small – one 8-byte packet can control three ESCs. Comms with the engine FADEC are also carried on this network. “We prefer to keep things simple,” Vander Mey says. “We have an elevator and rudder now, but we anticipate that when we go to scale production, we’ll probably just have a horizontal trim elevator, because the control is being accomplished fully with just the rotors.” Yonge adds, “The rudder is operated by a Hitec commercial servo, and a slow linear actuator from Thompson works the elevator. It’s slow because the elevator is mainly there for pitch trim, to balance the power being used by the front and rear rotors if we have an unbalanced CoG owing to how the cargo has been loaded. “Both servos run on the CAN bus, as does the BMS, and the latter connects directly to the flight controller for real-time monitoring of the power and battery status to adjust aircraft pitch so that zero net power is maintained. Beyond the CAN, there’s also a dedicated serial bus for the magnetometer and some avionics.” While a conventional multi-rotor might have three control loops for governing roll, pitch and yaw, the MAT’s flight logic is built on six. Its fourth manages horizontal airspeed, running from hover to forward flight, and is achieved largely through the propulsion engine, while the fifth is an altitude control loop that governs the rpm of the rotors. “In forward flight, that altitude loop still mainly just selects rotor speeds, but it also targets some minor pitch adjustments when climbing or descending,” Yonge explains. “The sixth control loop is for power management. That primarily targets pitch attitude in forward flight to achieve the desired net electric power consumption or generation from the motors. Technically though there are seven control loops in total, as all multi-rotors have something of an extra loop that ensures roll and yaw are coordinated during forward flight.” Collectively the loops are key to the ‘transitionless’ nature of the ATLIS’ flight. It behaves virtually identically to a multi- rotor at take-off, with the altitude loop defining the thrust and rate of climb, and once the target altitude is reached, the speed control loop becomes active and powers the turboprop (often with a sharp acceleration curve). As the ATLIS accelerates, the altitude loop reduces the rotor rpm, because less and less active rotor thrust is needed to support lift. “That would happen even if no wings were there, but as we’ve said, the ATLIS’ wing carries half the load,” Yonge says. Once in cruise (or even mid-climb and mid-descent later on), the power management loop goes from targeting a flat pitch attitude to targeting the required pitch for the desired battery recharge, as energy is consumed December/January 2023 | Uncrewed Systems Technology Each customised Emrax 228 motor produces up to 109 kW, although its high efficiency (96% peak) was of greater importance to Aergility than top-end power Although a rudder and elevator are installed at the tail, the rotors control attitude well enough that Aergility can omit the rudder and keep just the elevator for its final production version of the ATLIS