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44 primary control link is lost, the aircraft can enter a holding pattern. Alternatively, a back-up link – if a redundant 900 MHz link is designed in, as it is in many UAVs – can be used to conduct a controlled landing on a designated runway or other suitable terrain away from populated areas. Such a landing may also be recommended if a problem in the autopilot or inertial navigation system is detected, or if an actuator fails, if structural damage occurs or if an engine failure is impending. While the solution might remain the same in each case, listing the risk scenarios remains key. Delaying test missions is recommended if there are adverse weather conditions, such as rain or airborne dust, at levels above the intended environmental tolerances. Pre-flight simulations Access to accurate flight simulation is not only key to effective ground testing, it reduces risk by modelling flight patterns and anticipating potential failure modes. Running simulations also allows system specifications to be set as targets for when the time comes to conduct real- world flight tests. Top speed, cruise and maximum endurance, among other key specs, can be identified in this way. Furthermore, simulations can test the functioning of a UAV’s embedded software to verify that the autopilot has been programmed effectively before flight. Such a test might involve a computer simulating flight mechanical responses, setting flight paths anticipated during future tests and incorporating all processors, software systems and actuators. The GCS might be used as it would during actual flight, while the computer also models measured actuator commands and sensor errors. That means the testing crew can train and familiarise themselves with their roles in real-world operations to reduce the probability of human error and improve the quality of data collected later. Operations involving examinations of February/March 2018 | Unmanned Systems Technology Focus | Test centres System component validation UAV flight tests are also conducted for individual systems. Validating new components in the air as well as on the ground with an unmanned system architecture is valuable for proving the efficacy of new product iterations in their working environment. Testing a new subsystem in a more insulated enclosure than normal can be carried out to ensure that no overheating can occur during ordinary use. Stress-testing the system’s power consumption by running it at maximum – for example, by using a telemetry system at its maximum data transfer rate to see if the batteries and motor can handle it for the required period of time – should verify that the power consumption and power plant fit with each other. Repeated testing of launch and recovery systems such as catapults or nets is also critical to ascertain their survivability and that of the UAV’s own components with repeated use. Flying with simulated – or, time permitting, accidental – system failures can be vital to evaluating the performance of system redundancies. The failure of one or more motors on a multi-copter for example should be compensated for by the remaining motors, while a comms failure should trigger the activation of a back-up link. As for the GCS, testing it should include verifying that all flight-critical data (including any warning notices) are clearly displayed and updated in a timely fashion. All control interfaces (including the touchscreen, mouse, keyboard and various joysticks) should move freely and elicit the proper response during manual flight, and the GCS itself should not contribute to any undue latency issues. Guide to testing (cont…) Launch and recovery systems should be tested for consistent functioning and to ensure a UAV can handle their repeated use without damage (Courtesy of UAS Denmark)