Uncrewed Systems Technology 044 l Xer Technolgies X12 and X8 l Lidar sensors l Stan UGV l USVs insight l AUVSI Xponential 2022 l Cobra Aero A99H l Accession Class USV l Connectors I Oceanology International 2022

79 discover at length how this cutting-edge new family of power units has been engineered for the next generation of professional UAVs across the defence and heavy industry sectors. Inline three-cylinder advantages Having come from an automotive background, Hilbert has a predisposition towards inherently mechanically balanced engines, and the straight-triple is second only to the straight-six in this regard. “In the I3, because you have a firing order that allows the cylinders to fire at intervals of 120 º , both the first- and second-order vibrations of each piston’s combustion event are balanced by the motions of the other pistons,” he explains. “Basically, if you’ve got one piston going up, and the other two are at other points in the stroke, they directly counteract that first-order issue. Second- orders are more nuanced, and manifest more owing to the fact that the piston moves more rapidly in the upper part of the stroke than the lower part, but because of the 120 º firing order, those are inherently balanced as well.” The benefits of the firing order do not end there. With a cylinder firing at every one-third turn of the crankshaft, the intracycle torque fluctuations are reduced considerably compared to many other engine designs, particularly the boxer twins that are popular across the UAV world. “A boxer twin is essentially a big single-cylinder,” Hilbert observes. “Both cylinders fire at the same time, creating big accelerations and decelerations in rpm over the course of each cycle – in fact it produces negative torque between 180 and 360 º of crank turn, which inputs a lot of resonance into the fuselage that you really don’t want, especially for surveillance, mapping or anything else needing HD video or photography.” Vaglienti adds, “For as long as we’ve been in this industry, torque ripple has been the biggest source of the vibration we’ve been fighting in IC engine- powered UAVs. Even when dyno-testing our relatively small A33, when it spins at the resonant frequencies it makes the building shake. A boxer is far quieter, as its first- and second-order vibrations balance pretty well, but when you install it on an aircraft, the torque ripple sends vibration all the way through to the imager. In comparative terms, the I3 will be transformative for imaging quality. “Overall, when you go from a boxer to an I3, because your power strokes are balanced so well by compression strokes, you reduce torque ripple by a factor of around five.” While reducing torque ripple is perhaps the biggest benefit of the I3 design, it is not the only one. For instance, I3s trade out the yaw-oriented rocking couple inherent in boxer engines owing to the offset between its two crank pins (which can interfere with imaging stability) for a gentler, pitch- oriented rocking couple that most gimbals can compensate for much more easily. The I3 is also predisposed to better exhaust gas flow than boxers and singles. When the latter two designs fire, all the combustion gases are exhausted at the same time, and this pressure spike generates considerable noise. With the 1-2-3 firing order of the A99H, exhaust volumes are divided into three, and are evacuated smoothly from the exhaust manifold for much better noise filtering. “Every bit of noise and vibration you take out of the engine means better ISR [intelligence, surveillance, and reconnaissance],” Hoag says. “You can fly lower without being detected to get closer images of the ground, and you can zoom in more stably without the camera shaking, for better pixel resolution. “We ran mic tests on the A99 and our 100 cc twin. The A99 was always at least 6 dB quieter, even though the 100 cc Cobra Aero A99H | Dossier Uncrewed Systems Technology | June/July 2022 All the crankcase parts are printed on a single build-plate from AlSi 10 (with 0.1% manganese) before being machine-cut into their separate pieces