26 Dossier | AALTO Zephyr 8 at under 75 kg. Its empty weight comes to around 25-30 kg, making it lighter than most 1 m-diameter commercial multirotors. A combination of structural design, aerodynamic optimisation and lightweight parts contribute to its sizeto-weight ratio. In turn, at the time of writing its endurance had been tested over more than 64 days of continuous stratospheric flight – the current record for uncrewed stratospheric flight. Its engineering team aims to offer 200 days per flight of the Zephyr with essentially any variety of payloads up to 75,000 ft (22,860 m). The Z8 is now being positioned for commercial activities. With 20 years of r&d behind it, Airbus and Zephyr’s engineers have agreed that the HAPS’ days as a research project are complete. This is why it has been decided to switch the Z8’s flights from science experiments to commercial offerings. As a result, it is technically no longer the Airbus Zephyr: to transition it into a mission-ready platform, its team has spun out into AALTO HAPS (AALTO, derived from ‘Airbus, high ALTitude, zerO emissions’). It is an Airbus majority-owned but ultimately independent entity, its aim being to demonstrate its modularity, sustainability, technological maturity and very long endurance stratospheric flight for an array of missions. Providing 5G connectivity for instance is a primary aim, although AALTO also sees the aircraft as being suited for wide-area mapping and surveillance, akin to satellite imaging but without the associated launch costs. Early development history The Zephyr 2 was the brainchild of Qinetiq’s Chris Kelleher. He had studied the first solar-electric UAV, the Sunrise 2, flown at NASA’s Langley/Dryden Flight Research Center in 1974, as well as numerous humanpiloted solar flying machines such as the MacCready Gossamer Condor and the Gossamer Albatross. “Materials have come a long way since then, but you can see architectural similarities to those in the Z8,” remarks Richard Tyler, VP of flight operations at AALTO. QinetiQ was founded in 2001, and to make a name for itself it planned to set an altitude record using a large, crewed balloon aircraft named the QinetiQ 1. To take live photos of the balloon in the stratosphere, Kelleher suggested using a solar-electric fixed-wing UAV, for which the Zephyr 2 was designed as a 50% scale demonstrator. The full-scale aircraft was iterated in the Zephyr 3, a 12 m-wingspan UAV weighing 14.5 kg and integrating five motorpropellers. The team thought of tethering the Zephyr 3 to the Qinetiq 1 as the latter floated up to the stratosphere, where the UAV would spin up its propellers and fly around the balloon taking photos before the two descended together. The QinetiQ 1 failed to launch though, and the Zephyr 3 never flew, but interest from the UK’s MoD and within QinetiQ drove continued r&d in the Z3, the company winning funding in 2004 to develop the Zephyr 4 as a prototype for stratospheric ISTAR. This was also to be balloon-launched and tethered, the tether breaking under tensile stress to release the UAV. December/January 2024 | Uncrewed Systems Technology The Zephyr 3 was QinetiQ’s first full-scale attempt at a solar-powered stratospheric drone, and was originally meant for photographing a highaltitude crewed balloon aircraft
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