Unmanned Systems Technology 004 | Delair-Tech DT18 | Autopilots | Rotron RT600 | Unmanned surface vehicles | AMRC | Motion control | Batteries

28 There is no landing gear, as the craft is designed for belly landing, and there is some foam reinforcement to protect the payload bay on touchdown. Alternatively, it can be caught by a net to minimise the risk of damage on touchdown. Belly landing calls for an area 20 m wide and 40 m long (far larger than needed for hand launching, which requires only a few brisk paces). The DT18’s flaps have a large surface area relative to those of comparable UAVs, which allows it to obtain a steep descent towards its landing area. The steepness of descent needs to be decreased as it approaches the ground, then its attitude relative to the landing strip needs to be optimised for the best possible touchdown. The latter correction is currently operator-assisted rather than fully autonomous, but a satisfactory landing should normally be obtained without it. The ground station laptop has a joystick controller connected to it, of the type used for PC games. This is useful for pre-flight checks but in flight it is only normally used for this landing correction. Even then it is simply sending data to the autopilot, not controlling the craft as per a radio-controlled model aircraft. The craft normally flies autonomously between waypoints set by a click of the mouse on the map in question. The onboard GPS antenna needs to lock into at least six satellites to obtain clearance for flight, although the software also recognises GLONASS, the Russian equivalent of GPS, which means that as many as 20 satellites can be connected at once. The DT18 can be carried in a bespoke backpack and then, to improve portability, used with a small and light antenna, albeit one that provides a range of only 6.5 km. In some circumstances it can of course be used via wireless only. For maximum portability it can be used with a tablet rather than a laptop as the ground station. When using a tablet, thanks to the touchscreen functionality, there is no need for a joystick. Since the smaller antenna operates through a shorter range it doesn’t need to change alignment during flight, so its design is simpler and even lighter than it would otherwise be. Using this less powerful antenna there is no data transmission from either the airframe video camera or the payload camera. There is no collision avoidance system, other than the operator optionally using the video camera in real time on a see-and-avoid basis: in essence, the craft should be used in a zone segregated from other air traffic. Its route plan also needs to take into account the terrain, should an emergency landing be called for. Within the onboard control system there are different levels of contingency operation. Level one is simply to send an alarm back to the ground control station, while level two is the identification of a problem that calls for the mission Autumn 2015 | Unmanned Systems Technology Dossier | Delair-Tech DT18 As described in the text, the DT18 has an auto-diagnostic function that runs in parallel with the control process. Errors, once detected, are analysed and sorted, and an appropriate response is triggered. Five categories of alarms are defined, with the corresponding responses: Alarm level Response Group 1 Not serious for control Pilot informed or navigation plus specific actions Group 2 Control and navigation Stop mission not impaired Go to landing strip and land Group 3 Navigation impaired Land on site now Simplified landing procedure (can be overridden by the pilot in order to find a better landing spot) Group 4 Control impaired Flip vee-tail (deep stall) Group 5 Autopilot impaired Flip vee-tail (deep stall) (detected by external mechanism) Auto-diagnostics Elegant solution: a DT18 in action