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

87 Cobra Aero A99H | Dossier two to three. This controls the throttle position, cooling pumps, mixer valve, fuel injection and spark timing. At a higher level of control, power commands are received from the end-user’s flight computer in terms of rpm and/or throttle levels, with the ECU then arbitrating how best to execute these, rather than performing them directly. “Typically we want to limit the shear force with which the throttle moves, from a linear switch to a non-linear curve to deliver a curved power output,” Vaglienti says. “Aside from that, the engine is managed like any other: we have a crank position sensor for speed and timing readings, and we fire the three injectors and ignition systems to meet that.” A global ignition advance table details the crank angles that the front spark plug should fire at relative to TDC, with the other two following at 120 º intervals. Capacitive discharge ignition is used at present, as with the A33, although inductive discharge ignition might be adopted for both in the future. Another table maps out how much fuel should be injected relative to throttle position and rpm. “We also have injector ratio tables, which divide up the total fuel to, say, 31% to be injected towards cylinder one, 34% to cylinder two and 35% to cylinder three,” Vaglienti continues. “Because of the manifold geometry differences, you sometimes won’t have exactly the same richness or leanness between cylinders. The injector ratio tables account for that, and again they time it according to the crank angles.” The ECU can also command the generator controller for engine starting in the conventional configuration, and it will command the generator system for series hybrid control in an upcoming version. In both versions, another device performs generator commutation; the A99H’s commutation will use Power4Flight’s IntelliGen system, while the series-hybrid A99’s generator controller has to be more powerful. In all likelihood, either the Velocity ESC from Currawong or the VESC from Trampa will be selected. The generator can also be used to cold-start the engine (powering the glow plug as well as drawing on battery power to turn the crank) or maintain a given crank speed in the event of a fault or failure in order to execute a safe landing. IntelliGen meanwhile will enable additional capabilities. For instance, during over-cooling, it could first have the generator take over the power output function from the crank, then have it run the heater higher and open the throttle to undo the excess cooling and restore normal operation. “We also anticipate IntelliGen having the intelligence to recharge VTOL batteries in flight, enabling more flexible manoeuvring and hovering while reducing the need for intermittent landings and battery swaps,” Vaglienti says. Hybrid future The A99H’s developers are also working on a series-hybrid version called the A99S. This will be largely identical, save for a larger generator in place of the standard-issue alternator and prop, and capable of up to 4.5 kW continuous power output over a 70 V DC supply. “The front end of the A99’s core design is modular and can accept various configurations of generator and propeller, be it direct drive or belt-driven,” Hilbert says. “For one of the first deliveries of the A99S we’ll have a 5 kW generator and intercooler on the exhaust. “We’re also working on a gear head to mechanically translate higher shaft speeds into higher torque for running bigger, more efficient propellers, which we’ll be testing in a few months.” Vaglienti adds, “Cobra is working on its own in-house generator engineering facilities, and its first motor/generators will be liquid-cooled. Thermal management is going to get really challenging for multi-kilowatt generators as the UAV market’s power demands go up and up, so getting an early r&d foothold there is vital.” If the two companies’ r&d are any indication, further updates and enhancements to the A99 engine family will no doubt follow in the future, to match the growing needs of the UAV industry. Uncrewed Systems Technology | June/July 2022 A99H Spark-ignited two-stroke Inline three-cylinder 99 cc Case reed induction Naturally aspirated Heavy fuel and gasoline Liquid-cooled Fuel-oil mix: VP P4F heavy-fuel 50:1 pre-mix Maximum shaft power: 7 kW at 8500 rpm Peak generator power: 1.5 kW Specific fuel consumption at cruise: 500 g/kWh Weight: 3.65 kg Some key suppliers Throttle servos: Futaba Pistons: Vertex EFI: Power4Flight ECUs: Power4Flight Fuel pump: Currawong Engineering Oil: VP Racing Liquid coolant: Evans Waterless Engine Coolants Engine scavenging simulations: Convergent Performance modelling: Mod2T Structural optimisation (FEM): Altair HyperWorks Modal analysis: Altair HyperWorks Dynos: Tygerdyne Additive manufacturing systems (metal): Renishaw Additive manufacturing systems (polymer): HP 5200 MJF Specifications