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

82 yet been released as a product, we’d spent ages tearing our hair out over cranktrain robustness and crankcase stiffness, and we were determined not to go through that again,” Vaglienti says. “This time we were determined to nail all that from day one.” Much of the crankshaft design and simulation work experimented with different configurations, including whether to use four bearings or six. Notably the team eventually went with four, discovering that using six adds stiffness and strength but not durability. Using fewer bearings allows the crank to move more freely, and tolerate peak stresses better. “It was a full year of CAE investigating metals, mechanical parts as well as fluid dynamics, not just for charge but also optimising the coolant jackets, along with several other areas,” Hilbert says. “We’ve moved heavily towards Convergent for all our engine flow simulations. That’s a software tool that originated at the University of Wisconsin Engine Research Center, which handles moving boundaries and multi-phase really well. There are other toolsets out there, but we’ve seen Ford, GM and other big players switch to Convergent, so it seems to be the direction to be going in.” The first prototype print-outs for testing were produced in early 2019, and later that year some redesigns to optimise the cylinders and crankcase for AM were carried out. The first bench tests started in 2020, and more intensive dynamometer cycles had begun at the start of 2022. The first two customers for the A99H are anticipated to take delivery of their engines later this year. “We’ve worked to break the engines as much as we can,” Vaglienti says. “Tygerdyne’s dynos run our engines hard, but the data and engineering improvements that process yields are indispensable, and the power density and performance readings we’re getting are better than any 100 cc engine we’ve shipped before, and it’s quieter too.” As a final note on the advantages of metal AM, Hilbert notes that a typical loop-scavenged two-stroke has a hole drilled down from the lower cylinder to the crank bearing, to force oil down into the latter using the pressure wave of the piston’s downstroke. Rather than straight- drilling this hole, the A99H’s oiling holes can be printed, saving labour on drilling and in fact making the engine 12 mm shorter by printing curved holes (which are routed from the transfer port down to the bearing precisely where needed) rather than straight ones. Charge The throttle and plenum sit on the right of the engine, with a Futaba servo directly driving the barrel. “We’d spent unbelievable quantities of time dealing with the linkages in other engine designs; those took up maybe 20% of our r&d time so we got rid of them,” Vaglienti says. The intake manifold is additively manufactured using PA12 Nylon (the same material as the A33’s cooling ducts) on an HP 5200 large-format printer. Standard loop-scavenging is used, with June/July 2022 | Uncrewed Systems Technology Three injectors spray heavy fuel at 3 bar into each of the three sections of the crankcase, helping to prevent mixture errors which can be detrimental for spark-ignited heavy fuel engines The crankshaft went from a seven-piece design to a four-piece over the course of development, to improve its cost, durability and ease of assembly