54 Digest | Dufour Aerospace Aero2 Fuel versus payload The standard 40 kg payload capacity comes with an extra 12 kg of usable mass typically allocated to fuel for the estimated 3 hours of maximum endurance. Bendrey notes though that the weight allocated between the payload and the fuel can be redistributed as needed. “The nose is modular, so the cargo door could be swapped out for a panel with an integrated gimbal,” he says. “If that gimbal didn’t need to retract into the hull, then an auxiliary fuel tank could fit where the cargo payload would normally go, for something like a 5-10 kg total sensor payload and 42-47 kg of fuel, which would take the total range to more than 1000 km. “With 5 kg of payload and the remaining capacity being fuel, you could fly somewhere between 10 and 12 hours so long as you maintained the most efficient cruising speed of 130 kph.” Dufour estimates that for each extra hour of flight time over the 3-hour, 40 kg suggested figures for cargo missions, 4 kg of payload must be reallocated to fuel. That comes out at 5.5 hours of flight time with a 30 kg payload, 8 hours with a 20 kg payload, or 10.5 hours with 10 kg – the last of these enabling 1390 km or 750 nautical miles of range. For very urgent missions, the Aero2 can achieve an airspeed of 170 kph on generator power alone. Using all available power, a top speed of more than 250 kph is possible, albeit with the obvious tradeoff in endurance. While such missions might include high-speed deliveries of medical supplies or repair equipment, Dufour also promotes the Aero2 for search & rescue and public safety applications. For these, payload mass can also be integrated in the undercarriage between the landing skids, enabling a life raft or other similar items to be dropped wherever needed. Alternatively, that mounting point could integrate a synthetic aperture radar or other remote sensing devices that are too large to fit in the nose. Structure and materials Since the conceptual stages of the Aero3, Dufour has worked with carbon composites for their high durability-toweight ratio, and has continued doing so with the Aero2. The X2.1 therefore has a fully carbon airframe, as do the X2.2 and X2.3, with each iteration optimising weight, robustness and stiffness. “People think carbon is used just because it’s light, but while it is less dense than traditional aerospace metals, its fatigue performance is the real benefit,” Bendrey comments. “Boeing and Airbus are moving towards carbon airframes because they reduce the downtime that comes from inspecting for cracks and other flaws, so we too expect to have minimal downtime from structural repairs or overhauls over the Aero2’s lifetime.” Dufour has used mostly standard carbon cloth, with some unidirectional (UD) fibre for bending strength and stiffness in the wing, as well as in the load-carrying portions of the fuselage. The carbon also contains a lot of aero-structural foam, and as this is a lightweight material that cures at low temperatures, the company manufactures much of its structural parts with an aerospace-standard, low-temperature cure, single-cycle lamination process. The cloth, UD and resin systems come from Solvay, with parts manufacturing carried out by fellow Swiss companies Connova and Aerolite. “As we’ve accumulated flight data and flown every part and permutation of the transition corridor, we’ve been able to confirm and validate our own load cases, rather than rely on past aircraft load data to define our structural needs,” Bendrey says. “It’s been imperative that we investigate things like the aerodynamic interactions between wing, fuselage and tail, and remodel all of that in CFD software using Flow360. That gave us a suite of aerodynamic conditions and all the distinct kinds of landing conditions, which we then distilled into thousands of structural load cases. “Then, using Hexagon’s Patran for FEM and Autodesk Nastran as our solver, we’ve sized the aircraft structures and done more localised analyses of hinges and joints based on interface loads. It’s all traditional stuff from professional aerospace, to directly support the Aero2’s certification.” Dufour has also developed a patentpending approach to the design and manufacturing of its aerodynamic surfaces, such is the challenge of reaching its eventual target of 1000 Aero2 units a year – which Bendrey notes is double anything currently made October/November 2023 | Uncrewed Systems Technology Dufour has investigated aerodynamic interactions between wing, fuselage and tail, and remodelled them in CFD for aerodynamic and landing conditions
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