80 Insight | UAVs “That configuration helps Eterna deal with some of the aeroelastic stresses that HALE UAVs can induce when built with an overly large wingspan,” says Cyrus Shy, engineer at Windhover Labs. “We can integrate a range of payloads inside either fuselage, with up to 5 lb across them collectively, and we hope to increase that limit over time, pending better battery technologies becoming available to us as well as a cost-effective route towards quality solar cells.” Given the cost of flexible solar cell technology remaining high, Windhover continues to research ideal choices for maximising the weight-per-kilogram of energy generated onboard, while maintaining reasonable bill of parts costs for the eventual production version of Eterna. However, the growing availability of COTS solar modules is helping to keep their prototype testing and iteration costs low. “We successfully completed our first flight in early May, which validated the flight control and aero design, and our next step is indeed going to be solar panel integration,” Shy says. “A lot of the low-price modules we’re able to test with are quite flexible but still fragile, and some of the quotes we’ve had from solar material companies are really high but their quality is still tempting. One company we’ve met with can actually infuse the photovoltaic panels into carbon fibre and fibreglass lay-ups for a very well-integrated part.” As mentioned, advancements in batteries are also key to Windhover’s development plans, and any such innovations that enable low-price energy storage as well as weight reduction are especially valued; because, in addition to making a price-competitive HALE UAV, the company plans to optimise energy usage by ascending during daylight and descending (for lowered power consumption) at night, similar to other HALE companies like Aalto (see Issue 53). “One other method we’re planning on utilising for energy efficiency is utilising the jet streams of Earth’s atmosphere to propel Eterna around the world,” Shy continues. “It’ll take quite a bit more testing before we can achieve that; the UAV is designed for 8 g of force at the moment, which makes it pretty robust, but we don’t want to just assume it’ll be able to handle the fast-flowing air currents. “It’s pivotal for us to gather as much data as possible from those conditions at those altitudes, so we can understand what our in-house flight computer’s readings will look like when the UAV is flying in the jet streams, what the sensor data will look like and whether we can maintain our data links. That’ll definitely be a scary day when we direct Eterna into a jet stream for the first time, but we’re very much looking forward to it!” The Eterna’s flight computer product, Ravenity, sprung from the company’s background in aerospace control software and avionics as a fault-tolerant and certifiable system for autonomy and vehicle management. Meanwhile, the company is also working on Dragonfly, a tube-launched long-range survey UAV with military and civilian variations, both of which fly using Ravenity. Wildlife survey In addition to solar cells being a mainstay of stratospheric UAVs, low-altitude drones can also find their flight times and other capabilities enhanced through use of photovoltaics. The SW-117 UAV from Canada-based Superwake, which is a fixed-wing, catapult-launched, 5.3 m wingspan aircraft, is capable of flight distances exceeding 300 km through its solar wings and 2 kWh of onboard batteries. However, it originated from a research project aimed at breaking the world record for uninterrupted UAV flight (at the time of writing: 67 days, as set by the Aalto Zephyr earlier in 2025, extending its previous record by three days). “Over the course of our r&d, we opted to instead spin-off this more commercially-oriented UAV, which is ruggedised and purpose-built for a range of payloads and missions,” says Michael Melville, COO of Superwake. “We’ve designed the SW-117 with targets such as maximising the wing area, to fit as much solar cell material on there as possible – 80-90% of the wing top surface area is solar panel – and chasing weight-shedding in everything we can to grab every last second of endurance.” Among the applications for which the UAV is suited, the company notes that it has successfully carried out wildlife surveys in Canada, including deer and elk surveys in the Yukon territory and a broader ungulate survey covering Riding Mountain National Park (requiring flight over more than 3000 km2) in Manitoba. These missions utilised a NightHawk2UZ EO/IR gimbal from NextVision, August/September 2025 | Uncrewed Systems Technology Windhover Labs’ Eterna UAV is an upcoming stratospheric UAV featuring a distinctive dual-fuselage, tandem wing design (Image courtesy of Windhover Labs)
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