27 functioning with its own variable-pitch propeller and downstream rudder, to optimise the propulsion for efficient VTOL, hovering, banking or cruising at 70-90 kph. “Before starting development of this, our first UAV, we toured around the world to research what was being designed or built. No-one was developing anything quite like this, because it was deemed either too expensive, too complicated or too heavy. There were other claims, but those were the three main reasons,” Claes says. “So, in 2016, we resolved to make a technical solution that would be affordable, lightweight and reliable. We brainstormed a few ideas for a year and a half in a closed room before patenting them, two of which cover a couple of powertrain configurations that are the key to how we can build such big and powerful drones.” The first of those two patents covers the propulsion technology of the Thunder Wasp GT, the other three UAVs announced by ACC so far, and anything else it may build up to 2 t payload capacity. The second patent covers UAV powertrains of higher lifting capacities. It has been explored in laboratory and ground tests, with commercial exploration planned three to five years down the line. As well as both Drougges drawing upon considerable prior engineering experience, sustainable self-funding of ACC Innovation’s work (via profits from Ocean Modules Sweden AB and other successful ACC Group ventures) has enabled development of the large, turbine-powered quadcopter. Three units of the Thunder Wasp GT have been built, with 3.5 years of operation and over 100 test-flight hours (and over 700 takeoffs and landings) accumulated. As of writing, the company is focused on building three more units, as well as two Dragonfly (a smaller and differently configured quadrotor powered by a piston engine) – not for testing but sales purposes, and to research firsthand how best to transition from making individual units to series production. Series production will start properly in January 2025. Of the completed units, one will be delivered to ACC’s new partner, Fireswarm Solutions, in Canada (which has dedicated itself to distributing Thunder Wasp GTs for autonomous firefighting in North America), with another going to an unnamed defence customer. Strength, stiffness, simplicity Three criteria stand out to the Drougges as having been paramount development targets for the Thunder Wasp GT. One was robustness, in terms of fault-tolerant and failure-proof operations, ideally to achieve failure rates even lower than those of crewed passenger aircraft. “Uncrewed systems will be everywhere within the next 10 years, but if a pioneering system fails mid-flight it could set advancements in certification and funding back by years, so UAVs can’t function as well as crewed aeroplanes do. We really have to be better,” Claes says. For instance, when ACC first started prototyping, carbon composite was treated by most of the industry as a miracle material, so the earliest versions of the Thunder Wasp were built mostly with carbon parts, but when the team accidentally dropped a screwdriver onto one of the UAV’s pylon hulls it caused a small crack in the carbon. “That meant replacing the entire panel,” Claes says. “You can never repair a broken carbon body piece; you can’t undo a delamination or similar level of damage to the structural integrity of your craft, but aluminium can be directly hit with a hammer. It will certainly buckle, but it changes practically nothing of the lifespan or integrity of the UAV. ACC Thunder Wasp UAV | Dossier Aluminium can be directly hit with a hammer. It will certainly buckle, but it changes practically nothing of the lifespan or integrity of the UAV Uncrewed Systems Technology | December/January 2025 Almost every structural part of the Thunder Wasp GT is from a riveted, 0.4 mm aluminium sheet. After trying composites, the company opted for the metal’s repairability
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