79 FAA certification of the UAV, now named Kona, after the Pacific winds that interact with the trade winds, depends on its design being stable in air without needing an overly complex autopilot, hence Natilus’ exhaustive CFD. Aero simulations have validated the aircraft’s stability, so Matyushev says the design is mature and the Kona is at TRL 6, with expected flight endurance of up to six hours at a long-range cruising speed of 200-210 knots, a top airspeed of 240 knots and a flight ceiling of 22,000 ft (with an operating altitude of 12,000 ft). “We are now building its hardware in a 12,000 ft2 facility, and we’ve fed high-quality wind-tunnel data into the autopilot’s control loops to start software- and hardware-in-the-loop simulations,” he adds. “We’ve also done scale-model flight tests to validate the aerodynamics and the fixes we made following the first iterations.” Key contributors to the hardware at present include Collins Aerospace for the cargo-loading system, Janicki Industries for the airframe carbon composite, and Pratt & Whitney Canada for the engines. Two PT6A-67D turboprops will power Kona’s flight. These weigh 234 kg, measure 48 cm in diameter and produce 1,271 hp (or 948 kW), with a specific fuel consumption of 0.546 lb/hp (or 332 g/kWh). Their construction features a four-stage axial compressor, a onestage centrifugal-flow compressor, a one-stage gas-generator power turbine and a one-stage free-power turbine. “Within the power-plant categories we were interested in, it came down to either the Catalyst engine from GE Avio Aero [Issue 41], which is a cutting-edge turboprop, or Pratt & Whitney, which has been producing these engines for 80-odd years,” Matyushev explains. “The reliability that Pratt & Whitney engines are known for was a key selling factor to a lot of our customers. And if we’re going to sell this aircraft globally, having the global maintenance and support network of a P&W was a major factor in our final decision, especially if the engines will bring Konas and their freight to remote areas like the icy Canadian north or hot desert climates one day.” Long-distance inspection In the course of designing its VTOLcapable UAVs, FIXAR (FIXed Angle Rotor) applies its namesake technology stringently, its CEO Vasily Fainveits having found that VTOL-transitioning between vertical and horizontal flight is possible without needing tiltrotors if the lift rotors can be fixed at a tilted angle somewhere between the horizontal and the vertical. The Latvian company (which recently moved headquarters to the US) is best known for its first product, the fixed-wing quadrotor FIXAR 007 UAV, but it is now developing a remarkably different airframe configuration in its larger FIXAR 025 UAV. “Both UAVs use the exact same tiltedangle rotor technology, and the exact same lower-level autopilot control laws, with only some high-level changes in software between them,” Fainveits says. In developing a proprietary autopilot with the right logic for taking off and landing vertically using angled rotors, FIXAR also created proprietary data links, GCS solutions and airframe designs in the 007, with an eye towards optimising the payload-to-weight ratio (with the 007’s 7 kg MTOW, including 2 kg of payload capacity). “There were a lot of aerodynamic tweaks to get the 007 to perform as well as it does in such an unusual, specific shape, but as we looked into offering a bigger solution with a higher payload capacity, we had a choice: either try to scale up this existing design and get it to work in larger form, or work on something completely new to hit the higher carrying targets,” Fainveits recounts. “In truth, we prefer being creative over the boring work of scaling up existing designs, but also while thinking about the 007’s legs, especially how UAV legs can be a dead weight in not contributing anything in mission, I started thinking about my chair’s legs and how it didn’t need four of them. In fact, a three-legged chair is more stable on uneven ground than a four-legged chair is.” Those thoughts drove two engineering questions for Fainveits and his team: how could the UAV be optimised to VTOL on three legs rather than four? And how could the frame, legs included, be designed to contribute lift instead of being dead weight? UAVs | Insight Uncrewed Systems Technology | August/September 2024 FIXAR’s 025 UAV has an aerodynamic triangular wing, which doubles as landing struts when ‘tail-sitting’ on the ground (Image courtesy of FIXAR)
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