30 “The CAN buses extend down to those antennas, and the ubiquitousness of the CAN network means extra servos or payloads can be mounted quite flexibly across the airframe, depending on application.” Along from the engine is an external, belt-driven alternator, which can provide up to 1 kW of electric power, but ACC reports that the engine’s internal generator has proven sufficient to date for powering all flight-critical systems. A single, 4 kg, 15.6 Ah battery from EarthX in the US is installed under the engine, providing up to 840 A for starting power. It can also give emergency power to avionics in the event of generator breakdown, being a secure component based on LFP-type cells. The bulk of onboard energy comes from a mission-changeable, structural fuel tank in the bottom half of the central bridge of the body. “An extended output shaft from the engine sticks out further along, which we could easily mount something like a 5 kW generator on, if a customer needed that,” Claes adds. “Though this UAV [shown to us during our interview] has the engine exposed and visible, typically an aluminium fairing is riveted on top, safely enclosing it against external elements and making the aircraft look much nicer, although we tend not to use it in test flights, just so we can observe and access the engine easily.” Also key to test-flight observations are a number of GoPro cameras at the landing struts, inside the body and throughout the fuselage, which are installed to visually study every part of the UAV at each flight stage. Airframe validation While virtually every fairing and bulkhead is made strong and lightweight with the 0.4 mm-thick aluminium sheet, the airframe design has been developed to achieve a non-complex construction, a modicum of aerodynamics and a professional-looking aesthetic. “Obviously, the Thunder Wasp GT isn’t a high-speed aircraft. You can cruise 70-90 kph, but it’s a heavy-lifting crane in the sky, so the aero is just for smooth flight and some energy efficiency gains. Our Dragonfly UAVs will cruise at 150 kph and carry 200 kg for just two or three hours, but that’s a different use-case,” Claes says. In addition to considerable research in Solidworks, aerodynamic optimisations have been achieved using a test bench built in-house for trialling either one Thunder Wasp rotor or one rotor pylon with its two rotors integrated, which measures torque, thrust, rpm, efficiencies at different blade-pitch angles and myriad other parameters in advance of test flights. Rotors have also been mounted on road vehicles and driven down runways to simulate wind tunnels in outdoor conditions, as we have seen other developers do. “Though making a test bench for a unique aircraft construction isn’t easy, we did account for available regulations in designing it, which will be hugely helpful for certification in due course, given that no specific certification regulations exist for this type of large, heavy-lifting UAV just yet,” Max adds. Also key to that will be ACC’s own flight range, roughly 400 m away from its headquarters, which was approved by Transportstyrelsen (the Swedish Transport Agency) in March 2024. It has enabled rapid testing and evaluation of new iterations, modifications and components in the company’s UAVs over the past year. Industrigallerian However, the ACC Group’s headquarters may be the biggest reason why ACC Innovation is making it to series production and working towards Type Certification after just five years of physical r&d (other, larger OEMs have tried for longer, only for their uncrewed ventures to fall by the wayside). “We followed a clear plan, and one target was for our first UAV seriesmanufacturing space to be ready by the start of the winter holiday in 2024. We hit our deadline, so now we have a brand new production facility here, with laboratory levels of cleanliness and traceability,” Claes says. “As mentioned, we’re working on three Thunder Wasp GTs and two Dragonfly to learn firsthand how best to organise our series production, but a critical partner we’re doing that with is Scanfil Åtvidaberg AB, which will be the contract December/January 2025 | Uncrewed Systems Technology Dossier | ACC Thunder Wasp UAV Being able to perform test flights quickly in its own flight range has greatly aided the speed with which ACC can engineer and optimise UAVs
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