Uncrewed Systems Technology 048 | Kodiak Driver | 5G focus | Tiburon USV | Skypersonic Skycopter and Skyrover | CES 2023 | Limbach L 2400 DX and L 550 EFG | NXInnovation NX 100 Enviro | Solar power focus | Protegimus Protection

7 Platformone Uncrewed Systems Technology | February/March 2023 Flowcopter, in Edinburgh, Scotland, is developing a UAV that can carry up to 160 kg (writes Nick Flaherty). The 500 kgUAV uses Digital Displacement transmission technology that ismuch lighter, more robust and less costly than an equivalent electric transmission. TheUAV uses a type-certified engine froma light aircraft with a hydraulic transmission that allows the cylinders to be optimised in real time using fast digital control to drive rotors for vertical lift. The hydraulic system has four separate subsystems, all of which share a common low-pressure connection to a return line that is pre-charged by a pneumatic bladder accumulator. Each rotor subsystem has an independent fluid supply from the pump, which supplies fluid to a fixed-displacement bent-axis hydraulic motor, which also acts as the rotor hub. Each rotor subsystem has a pressure sensor and motor speed sensor. A systemcontroller sends pressure demands for each rotor circuit to the pump controller, which is a specialised electronic controller consisting of amicrocontroller, FPGA and power electronics. The digital displacement pump consists of 12 cylinders arranged in three banks of four along a common crankshaft supported by roller bearings. Each piston bears on the crankshaft by hydrostatic pad and seals by a spherical metal piston ring. Each cylinder has two commutation valves, which are both built into a single valve capsule. That drives the bent-axis hydraulic motors to drive the propellers for the lift. However, this has required a new design of propeller, as the motors operate at lower speeds but require more power. MagCAD, in Germany, has designed and produced the 2.2 m-diameter props for a demonstrator with a speed of 1800 rpm for hovering and up to 2100 rpm for horizontal flight. A hinge helps with the torque and for transport. “We have specific needs for the UAV on the torque-to-power ratios where we matched the hydraulic lift motor to the propeller using the MagCAD software, and that gives us more lift for a given power than from an off-the-shelf propeller,” said Uwe Stein, technical director of Flowcopter. “We are now looking to go bigger, for crop spraying and logistics, and we have a project with the Warsaw Aviation Institute where we are looking at our technology for a transitional UAV,” he said. “The transmission can syphon off power for four bent-axis lift motors on the wings, so we can get 40 kWout of the 5.5 kg motor. They have an incredible power-to- weight ratio and robustness,” he added. “Hydraulics has always been seen as a robust and low-cost technology but also as inefficient and not very controllable. By enabling and disabling cylinders we reach 95% efficiency, putting us on par with electric transmissions but cheaper and lighter.” The UAV is currently being tested. Airborne vehicles UAV is a heavy lifter A hydraulic transmission and a new design of prop contribute to the UAV’s carrying capacity