40 10-12 paces before letting go. After it reaches a few metres/second, the wings generate lift, and for the motors and propellers initiate the climb. “We’re working on a launch system for greater automation, but we have to consider the different environments they might be used in, to ensure they’ll operate from sea level up to 7000 ft. That mandates a wide range of launching speed and distances,” Tyler comments. The ADS-B Out and In systems are vital for tracking and identifying other craft and their trajectories during ascent. In the event of data link congestion or losses, the flight controller will automatically toggle onboard radios to hop between frequencies. To cover all air traffic requirements, the Z8 integrates the ping200X transponder from uAvionix as its Mode S transponder with extended squitter (and hence ADS-B Out) for transmitting its ID, GNSS position, altitude and velocity. ADS-B In receives data on the nearest targets, and issues any necessary avoidance manoeuvres during ascent or descent. Links are also encrypted to guard against spoofing or replays of the Zephyr’s own data in comms or GNSS. Counters are designed into the flight controller to ensure the comms and navigation data from the multiple onboard sources all match up with each other, with no sign of anyone forcing a replay of a command the GCS crew might have sent, such as a 180o turn made to avoid an issue ahead. “And we can fall back on IMU dead reckoning at times; we’ve tested that a lot,” Tyler muses. “One of the joys of occasionally working on US military ranges is that they start trying to jam you. We’ve had situations before where we experienced periods of lost comms, and learned over the phone that ‘some guys were doing some testing’, but we were able to switch frequency to resolve the issue, but then rapidly lost comms again. That’s kept us on our toes and given plenty of opportunities to prove how the Zephyr can keep operating safely without us, if required.” Flight operations At the time of writing, 75,000 ft was the peak barometric altitude set by the Z8, with 76,149 ft being its peak measured GPS altitude. Indicated cruising airspeed during operations hovers around 1617 knots, “That seems absurdly slow, but as we fly higher, our true airspeed increases relative to indicated airspeed, and as such, generally our ground speed increases too,” Tyler says. “If there’s no wind, we’ll actually cruise at somewhere between 50 and 60 knots ground speed, which means we can cover 1200 miles per day. That’s how the aircraft managed to fly from Yuma in Arizona to Belize within the month of July 2022.” For solar efficiency, most flights have been near the equator, although AALTO will serve other latitudes, the limiting factors being the shortness of the day and the length of the night. The aforementioned surplus energy generation from the solar cells means that in daylight, the Zephyr climbs while charging its batteries. At night, when the sun and solar recharging are absent, it draws power entirely from its battery stores and descends, reducing the power drawn by its motors and shifting some of the flight burden to its wing-generated lift. The Zephyr can therefore operate wherever there is enough daytime to climb and charge for long enough for full coverage of the subsequent night-time energy needs. Tyler points out however that most of the world’s population lives closer to the equator than the poles, and that the Zephyr does not need to launch precisely where it will be operating. As it can cover nearly 2000 km each day, it can circumnavigate the Earth within 21 days, although as wind is used when maximising flight speeds, flying in a straight line from a launch point to a mission location will sometimes take more time than travelling in a physically longer route around the planet. As mentioned, AALTO’s record is a 64-day (plus 17 hour and 43 minute) flight from June to August 2022, from Arizona to Belize. This was 3 hours shy of the world record for the longest flight of any aircraft, and beat the UAV’s previous endurance record by over 150%. The flight accumulated a huge amount of engineering data and took over 4500 photos in a single day, until a large thunderstorm formed, covering the entire operating area for the Zephyr. That caused severe turbulence and led December/January 2024 | Uncrewed Systems Technology Dossier | AALTO Zephyr 8 With favourable weather and ATC clearance, the Zephyr is hoisted up for hand-launch by several personnel. They take 10-12 paces before the HAPS glides on its own lift
RkJQdWJsaXNoZXIy MjI2Mzk4