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

34 Dossier | Aergility ATLIS was a bigger challenge. Aergility needed a full four-quadrant ESC with speed control and forward and reverse rotation. While doing wind tunnel testing (at Lockheed Martin’s facilities) the company found that the motors would sometimes need to spin backwards to avoid producing excess thrust, so efficient operation over the full range of positive to negative rpm and power was key. “APD’s motor controllers use SiC transistors, which have very low switching losses and hence extremely high efficiency – around 99% in fact – when the ATLIS is in hover,” Yonge comments. “When in forward flight, at near 0 W net consumption, we still need really efficient power transistors switching power back and forth between the motors and our 400-450 V batteries. By comparison, typical FETs would be wasting quite a bit of power through that switching.” SiC’s efficiency also reduces the amount of heat that has to be dissipated compared with FET-based ESCs; Aergility estimates a 75% reduction. “The ESCs on our test rigs from 2015-22 would be covered in huge heat sinks because of the dissipation needed for the switching,” Vander Mey says. “Using SiC means we don’t need sophisticated cooling arrangements for the 3 minutes we spend hovering, during which we might otherwise produce several thousand watts of heat.” The electric motors are custom-designed versions of Emrax’s 228, built around tapered needle bearings to withstand the unusual moments of MAT flight and hence ensure the motors can still have MTBFs greater than 10,000 hours. Aergility is also collaborating with an undisclosed supplier on a high IP-rated e-motor design for flights in extreme weather. The Emrax 228 produces 109 kW peak and 60 kW continuously, although the ATLIS does not require such high power or the associated rpm; instead, the high efficiency (96% peak, 94-95% during the ATLIS’ hover) is cited as a primary appeal. Turbo propulsion Power for forward propulsion comes from a Turbotech TP-R90 (explored in detail in UST 31, April/May 2020). It is a 90 kW, 80 kg micro-turboprop built around a heat exchanger composed of microtubes that recuperates the otherwise wasted exhaust gas heat to preheat intake air. That air thus requires less fuel than usual for combustion and power, roughly doubling the overall fuel efficiency (to around 19 litres/hour) compared with regular microturbine designs. This, and lowering both the emissions and noise, made it ideal for Aergility’s solution. “It was too challenging to find a reciprocating engine that could run on heavy fuel and still provide the power we wanted, and the rotary engines we looked at were too expensive and didn’t have long enough TBOs,” Vander Mey says. “Not only does Turbotech’s engine run on widely available jet fuels and diesels, it can run smoothly on a range of sustainable fuels, like biofuels and eventually hydrogen, which is going to become more and more important in many areas. Its 3000-hour TBO is great too – it’s not a cheap engine, but that kind of runtime pays for itself after a short while.” Yonge adds, “Also, the heat recuperation means it maintains the December/January 2023 | Uncrewed Systems Technology The ATLIS is powered by a TP-R90 micro-turboprop, a 90 kW, 80 kg engine that is about twice as fuel- efficient as conventional microturbines The engine comes with a variable- pitch propeller for further efficiency during take-off and flight