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54 Digest | ElevonX Sierra VTOL and you need either a more powerful sensor payload or more flight time, or both, to gather more of it.” Looking into different wing configurations to increase both carrying capacity and flight endurance sparked the idea to modularise the wing and tail components. The first stage of the project focused on designing and optimising a fuselage and integral payload bay for different aircraft configurations. “The first prototype of the SkyEye Delta, again a flying-wing aircraft with a small footprint, was flying in May 2017,” Langus says. “We learned a lot from its trials but soon realised that the market really wanted VTOLs, so from November 2017 we started working in earnest on a pathway towards the SkyEye Sierra VTOL. In January 2018 we 3D-printed a small prototype of it to test the autopilot’s capabilities and mature the workings of the VTOL transition.” The team also tested different propulsion arrangements across various mission types and flight patterns, until they settled on a configuration that could transition and generally operate to a quality and standard that would outperform the typical market offering. Following this, between February and March 2018, they focused on simulation software for optimising the aerodynamic design, then went through rapid prototyping to create a full-scale version they could trial in the air, with flight testing and validation between June and October 2018. Designing and modelling the final version of the Sierra VTOL followed soon after, and was completed in February 2019. Being satisfied with its performance, cost and componentry, ElevonX completed the moulds for this version in June 2019, marking the readiness of its scale production faculties. “We test-flew the final, production version of the UAV from November 2019 to January 2020, and spent a lot of that time using the flight data to optimise the autopilot and other software items,” Langus says. “In February 2020 we decided we were completely satisfied we’d made a UAS that was ideal all-around, and made it available to our customers.” During these years, the company also produced the Sierra, the forerunner to the Sierra VTOL which has the same wing and tail configuration but without the lift motor booms. Alongside the Delta, the company developed its Scorpion catapult launcher, which is used for launching the Delta and the Sierra but is also available for launching third-party UAVs. System architecture The payload bay is installed in the front of the fuselage, and the propulsion system is installed in the back. The Sierra VTOL has a pusher propeller configuration to keep the centre of gravity (CoG) in the centre of the craft, and this also moves the prop’s blades out of the payload’s field of view. “We wanted to maximise the space for the payload and associated electronics in the fuselage, so we’ve aimed to move as much of the non-payload avionics into the wing as possible,” Langus says. “The wing is about 3 m long; the middle third contains the autopilot, parachute and GNSS antenna. The left wing contains the pitot tube and telemetry radio, and the comms radio is in the right wing. “We’ve also maximised the distance between the two radio data links to minimise interference, and we keep a small distance between the autopilot February/March 2022 | Unmanned Systems Technology Payloads such as this YellowScan Lidar are used by ElevonX’s customers in mapping and surveying missions The Sierra is being used in a number of new applications such as postal services, environmental measurements and emergency medical deliveries