30 Dossier | AALTO Zephyr 8 Zephyr 8 anatomy At the time of writing, 12 Zephyr 8s had been produced and flown in eight flights, for over 3000 cumulative operating hours. The company estimates that the total flight time across all Zephyr models exceeds 4000 hours. As mentioned, the Z8 was briefly redesignated the Zephyr-S, and promoted alongside a twin-tail version called the Zephyr-T, although the latter was internally named the Zephyr 9 (which to date has not been actively flown or optimised for commercial service). Those names did not catch on within Airbus or AALTO, so they have been discarded to avoid confusion. Outwardly, the Zephyr’s shape looks little different from a conventional aircraft. It has two fixed wings that connect to a single fuselage, and each wing has a propulsion unit consisting of a motor and propeller, while a payload pod sits at the front of the fuselage and there is a tail at the back. The tail mounts a fin, an elevator and a rudder. Unlike typical fixed-wing UAVs, however, the fuselage consists of a carbon tube and contains only cabling, with very few subsystems inside. Instead it serves primarily as a structural member, connecting the tail and the wings, with the bulk of subsystems mounted in the latter. “Of course, there are quite a few other differences to a conventional fixed-wing UAS, such as our extensive use of solar power, and the fact that our aerostructure and propulsion system are optimised for flying in the stratosphere, not for the air densities and environmental conditions near ground level,” Tyler notes. “On top of that, we have to design for really unusual thermodynamics throughout flight. I sometimes liken it to an astronaut doing a spacewalk: when the sun’s on one side of their spacesuit, it is practically on fire from the sheer heat, while the other side is below freezing. “The Zephyr goes through a comparable cycle over each 24-hour period. The stratosphere can be -50 oC ambient during clear days but the sunlight shining down on the solar panels heats up all the topsides of our components really strongly. And it’s much worse on overcast days, because the sunlight reflects off the clouds below to cook the undersides of the wings and subsystems. “In terms of our mechanical structure, we heavily span-load the wings with our componentry. We have no undercarriage, and every gram of weight installed and every milliwatt consumed must pay for itself in a net benefit to overall SWaP before being approved for use – 75 kg is our maximum all-up weight. “Combine that with our 25-30 kg empty weight and 25 m wingspan, and you find we don’t actually fit into any definable group or category of UAV.” Each wing consists of three sections – the main wing, which connects December/January 2024 | Uncrewed Systems Technology Internal components are largely span-loaded along the Z8’s wings, with comparatively little componentry in the fuselage
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