Unmanned Systems Technology 042 | Mayflower Autonomous Ship | Embedded Computing | ElevonX Sierra VTOL | UUVs insight | Flygas Engineering GAS418S | Ocean Business 2021 report | Electric motors | Priva Kompano

58 air measurements with its own unique sensors and is in dire need of a VTOL capability. “As a small company, we can quickly adapt our payload bay to accommodate all kinds of new systems, and the UAV stays very robust. The researchers at Tubingen actually flew their Sierra VTOL in a BVLOS mission in the North Sea recently; it was battered by North Sea winds but still returned home intact.” ElevonX also uses and supplies the peRISKop GCS from Hungary-based Horus, which has extensive experience in integrating different kinds of data links. The comms link between the UAV and the GCS typically operates using the MAVLink protocol and transmits over an 868 MHz or 900 MHz frequency, with a 57 kbit/s data bandwidth and up to 1 W of output power. This gives a maximum effective comms distance of 20 km (although transmissions over longer ranges are of course achievable), and an RC PPM back-up transceiver is also installed for further redundancy. “The peRISKop has a simple arrangement, with just one cable running from the ruggedised computer to the standing antenna,” Langus says. “That works great for us and our users, as there’s a minimal amount of peripheral equipment to break or lose.” Lastly, there is the safety-critical parachute, which was originally developed for early ElevonX UASs in-house by a member of the team. However, the company wanted an aircraft-certified parachute, and after some searching found Galaxy GBS in the Czech Republic, which is known for producing certified parachutes for general aviation and ultralight vehicles, as well as some smaller ones for UAVs in more recent years. “Those smaller parachutes have been tested by the Czech Military Research Institute, and there is now a specific certification category for parachutes in UAVs, which made things very easy for us,” Langus recalls. “It works using a pyrotechnic gas generator, as with airbags and some other UAS parachute products. There’s a tube with a parachute folded inside and the pyro-generator underneath, and when triggered it pushes the folded parachute up, out and away from the airframe. That’s primarily to avoid entanglement with any of the propellers, and it also means it starts catching air and slowing the descent of the aircraft immediately. “It can be triggered remotely by an operator, or the autopilot can detect a rapid loss of height that wasn’t pre- programmed or commanded, and automatically deploy it.” Navigation The Cube Orange, from CubePilot, is used as the Sierra VTOL’s autopilot, and accordingly the team’s choices of navigation systems encompassed most of the well-known Pixhawk ecosystem of components. For instance, a Here3 GNSS receiver takes satnav signals from Galileo, GPS, GLONASS, and BeiDou satellites, and transmits them as data to the Cube. “The Cube Orange has a very good processor, but even more important to us is its triple redundancy – it has three accelerometers, three gyros, a magnetometer compass and two barometers for height estimation,” Langus explains. “Reliability is key for professional UAV operators, and the three inertial sensors are also vibration- damped inside the enclosure. “They are also temperature compensated. CubePilot installs a small heater in the system to keep them at about 60 C during flight, at which they’re most accurate.” He notes however that ElevonX typically does not use the Cube’s internal magnetometer during navigation, as devices packaged in this way are often sensitive to EMI and signals from other avionics. Instead, the Here3 is packaged with a magnetometer of its own, and as mentioned the receiver is spaced apart from sources of interference. This ensures the GNSS and the magnetometer readings are undisturbed and that their integrity can be trusted. “In most of our test flights we’ve never needed to fall back on a second Here3: under all flight conditions we’ve always picked up at least 12 to 14 satellites, with very precise data,” Langus adds. “But the Cube Orange allows you to plug up to three receivers into the autopilot, which then filters the signals to determine which is giving the most reliable reading, providing dual-redundant GNSS. “We already know how to position the GNSS receivers and antennas in the RF-transparent sections of the wings to achieve that, as there’s still enough space to minimise EMI under this configuration.” The pitot tube is fairly standard, although Langus adds that the pitots (from Matek Systems) gave the most stable readings, whereas some others occasionally gave peculiar readings, probably owing to February/March 2022 | Unmanned Systems Technology A standard-type pitot tube from Matek Systems was selected for its stable performance. A heated pitot is also available for those who will often fly in rain or snow