49 in emergency medical transport. That focus looked much more impactful and interesting than most of the eVTOL concepts I’d seen – which were largely just air taxis – so I left my previous company and joined Dufour to develop flight control systems with Thomas and Dominique.” That crewed eVTOL concept is now called the Aero3, and is planned to be a 2800 kg aircraft with a 13.6 m-long tilting wing, occupying a similar footprint to typical medical transport helicopters. However, the three co-founders and their team decided first to develop a scaled-down prototype (as is conventional), the X2.0, to demonstrate the tilt-wing technology and prove its mechanics, aerodynamics and stability. “Potential customers were enthusiastic, and asked if we could sell them the demonstrator model,” Kent recalls. Finding a huge market potential for a UAV of the X2.0’s size, a flight testing programme using the X2.0 was carried out in 2020, and in 2021 active product development of the Aero2 concept began. As part of this, the first iteration was the X2.1, which was far larger than the X2.0, and involved more rigorous design optimisation as well as bigger e-motors and batteries. The second was the X2.2, which is designed with series manufacturing in mind and which Dufour is currently flying for its r&d and test data. “The next version will be the X2.3, which will be our pre-series production prototype with a range extender,” Kent adds. “That will lead directly to the series production aircraft, and we expect to start flying it early next year.” System architecture The Aero2’s layout is designed around the range extender, it being the largest and heaviest single component in the UAV. As it will make its debut in the X2.3, Kent points towards that iteration as the one for understanding Dufour’s engineering. “The range extender consists of a Suter Industries engine and a Plettenberg motor/generator,” she says. “It’s positioned forward of the aircraft’s centre of mass [CoM], just ahead of the wing on the upper fuselage area, effectively providing a forward throw of mass to balance the UAV. “Underneath is the payload bay, which is accessible via a hatch at the front of the aircraft. End-users slide their cargo under the CoG, which keeps the Aero2 from being too sensitive to weight changes. Our fuel tank is also accessible via that hatch, a little further back from the payload bay.” To keep the batteries from affecting the CoM, the battery modules are distributed around the aircraft. That also reduces the required mass of cabling, with power going directly to the e-motors from local modules. It also prevents failures in one battery or motor from affecting the rest of the aircraft. The Aero2 has a total of five electric propulsion motor-propeller pairs – four tractor motors on the wing, and one at its tail – with bespoke variable-pitch propellers designed for efficiency throughout all stages of the tilt-wing flight profile; the design is currently being evaluated on Dufour’s test bench. The tail motor augments lift from the main motors and provides pitch control during hover and low-speed transition. Lastly, there is an avionics bay in the upper fuselage, just behind the wing. The avionics are accessible via a panel for maintenance. Tilt-wing transitioning Development of the tilt-wing mechanism took inspiration from past crewed tiltwing aircraft such as those mentioned earlier – in fact the flight manual and history of the CL-84 played a key part. “There’s a lot of other information available,” says Simon Bendrey, head of design at Dufour. “For instance, the US National Advisory Committee for Aeronautics developed aerodynamic profiles suitable for tilt-wings during the 1950s, with specific aero profiles for the wings and tail, specific locations for Dufour Aerospace Aero2 | Digest Uncrewed Systems Technology | October/November 2023 The Aero2 features five electric motor-prop pairs – four on the wing, and one at the tail
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