Unmanned Systems Technology 017 | AAC HAMR UAV | Autopilots | Airborne surveillance | Primoco 500 two-stroke | Faro ScanBot UGV | Transponders | Intergeo, CUAV Expo and CUAV Show reports

76 Focus | Transponders increasingly with pressure altitude encoders, GNSS, Mode S and ADS-B integrated in a single package, certified according to the pertinent standards, as developers anticipate the difficulty of designing a UAV’s internal architecture to accommodate separate units for each one, and arranging them to minimise factors such as conflicts over space, heat dissipation and excessive cable weight. Integrated pre-certified systems also makes it easier for a user to operate a UAV, as it helps with the safety case. An operator can install such a system into their aircraft without worrying that it will breach the terms of the certification. That said, solutions such as payload- style transponders that are not designed to integrate directly with a UAV’s autopilot or other subsystems are emerging as an option. UAV operators who take that route would not be able to exploit ADS-B In though, as any replies received from surrounding aircraft could not be communicated back to the ground control station (GCS) and would therefore need an alternate approach to observe such traffic. This option can be less complicated and cheaper, however, as setting up the device independently of the autopilot does away with the need for software or electrical integration inside the vehicle. That may also allow UAV designers to place the transponder wherever there is space, without having to worry about physical interfaces such as the outer body of the UAV or inside the tail, and with the transponder orientated vertically if GNSS has been integrated. Environmental testing Whether the transponder is mounted outside or inside the airframe, UAV designers and operators need to prepare for carrying out missions at various altitudes and latitudes. Certification in particular requires a lot of testing to ensure safe and reliable performance in all conditions. For example, during development a transponder might go through DO- 160G, the FAA’s minimum operational performance standards for environmental capability in airborne equipment. These involve laboratory testing for parameters including temperature, shock, vibration, salt spray, humidity, icing, flammability, indirect lightning testing, as well as RF interference testing. Modern transponders may need increasingly stringent environmental testing and design. In the past, transponders designed for general aviation could be placed anywhere on a large aircraft without having to worry about any damaging interplay between other systems. UAVs, however, particularly smaller ones, have limited internal storage space, and placing two avionics units next to one another could create hazardous levels of heat. Minor innovations in unit mounting, such as the use of a certified tray or judicious selection of fasteners can therefore do much to minimise heat or other unwanted interactions between subsystems. Ground control stations To comply with regulators’ and ATC requirements regarding airspace safety, ground operators of UAVs must remember that preparing their transponder for flight demands that all necessary information must first be loaded onto it from the GCS. In the case of Mode S, for example that will include the 24-bit ICAO address, so any GCS programmed only for Mode C operations must be updated with Mode S software. As talks on standardising transponders and related UAV safety regulations continue, ground stations might in future be required to integrate some form of primary radar. That is because airborne radar becomes attenuated close to the ground, and UAVs need to be clearly visible at low altitudes, where other manned aircraft may be operating. Antenna integration Selecting and fitting a UAV’s antenna needs to be carefully considered to avoid the problem of signal blocking caused by airframe shadow. Traditional transponders designed for high-power systems could partially overcome this but the newer, low-power designs can be blocked far more easily. December/January 2018 | Unmanned Systems Technology Adding a transponder can generate excessive heat inside the body of a UAV, but including a certified tray will pre-empt that (Courtesy of Trig Avionics)