This write-up presents a description of the Unmanned Air System (UAS) for a radio-controlled (R/C) aircraft using a reliable and stable Ardupilot autopilot system. The mission for the UAS includes autonomous navigation and target recognition system by use of an RMRC 480N video camera that transmits video in real-time to an imagery station through a wireless communication link. Different fail-safe measures have also been considered to ensure the safety of the UAS.
Administrative Data
The UAS that will be used will be a modified version of Courage- 10 aircraft which is a radio-controlled aircraft (RĂDUCANU and CÎRCIU, 2017) . The UAS will consist of three main subsystems, that is flight system, ground system, and payload.
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The flight system includes the airframe custom developed to realize the mission requirement and the autopilot system in charge of the autonomous operation of the airframe. A ground station laptop is responsible for controlling the autopilot enabling the operator to control the aircraft, view aircraft diagnostics and upload flight plans.
Fig: UAS
The payload comprises Ardupilot for handling the autonomous navigation, a camera system for telemetry, transmitters and power supply. The camera/telemetry system will consist of an SRIC module, RMRC 480N sensor, and Sony CCD video camera that has the ability to shoot video with 480 TV-line resolution. Every payload component is contained in different custom-developed containers on the UAS with standard interlinks for communications and power supply to ease maintenance (Papageorgiou, 2016) . The computer on the ground control station receives serial feed from the onboard autopilot system containing all telemetry data essential for geo-referencing the pixels in every video frame in order for the target’s GPS coordinates to be traced (Thumser et al., 2017) . The ground control station also has a separate imagery reception system from the on-board camera and system for identifying targets and their features.
Fig: Ardupilot
The control station will consist of a laptop linked to an XBEE PRO 900 XSC module via a USB cable. The working frequency and baud rate are at 900MHz and 57600 respectively. A 2.1 dbi rubber duck antenna is linked to the XBEE also, an XBEE antenna that is similar will be mounted on the UAS which will, in turn, be linked to the autopilot. To avoid interference from similar devices, the XBEE modules will be paired prior to flight.
The ground control station software will be APM on windows OS. The use of the APM is performing analysis of telemetry and mission planning. The graphical user interface of the APM displays location, altitude, attitude among other important data like airspeed, throttle percentage, battery voltage, and general direction of wind. As a result, full situational awareness is enabled hence assisting the ground control station operator to ensure the safety of the UAS.
Fig: APM
Flight Data
The mission for the UAS is intended to take 25 minutes. The UAS will fly at airspeeds of between 40km/hour and 60 km/hour. The UAS will fly at a maximum of 400 feet. The flight path is determined by the use of waypoints through which the UAS is expected to fly. Waypoints values are created using PID which are set for pitch, roll and yaw servos. As such, the ardupilot computes the required movements for the respective control surface to reach the destination thus allowing the UAS to navigate from one waypoint to the other and matching its present location to the next as is in the mission plan.
Fig: navigation PID
Fig: planned flight path
The 11.1V, 5000 mAh Lithium Polymer batteries are used to power the 12V payload, they can power the aircraft up to about 25 minutes. The voltages of the battery are constantly monitored by the ground station operator with the aid of the APM. If the voltage drop below the threshold, the UAS is landed and another battery replaced.
The operating frequency of the on-board transmitter will be 1.28 GHz for target identification. This will allow video output to be sent to the ground station. The crew/ controller will utilize a frequency of 900MHz to communicate.
In the event of an emergency such as the autopilot losing control, a safety remote control is used. Futaba T7C remote control will be employed in this case. It operates on a band of 2.4GHz. A switch on the remote establishes if the UAS is flying autonomously or under the safety pilot’s control. The planned flight area should be clear, such that if the aircraft loses link it can land within the prescribe mission area.
Across the entire mission, VLOS will be maintained. To do so the ground station controller will be located at or near the center of the planned flight path.
Mission Data
The mission requirement for the UAS is to take videos. It will transmit images of targets to the control center on the ground.
Safety Data
The use of UAS may have some limitations like restrictions on airspace use, weather hazards or component failure (Hamilton, Bliss and Depperschmidt, 2017) . The UAS will be restricted to fly withing set waypoints and restricted airspace. If you fly within 5 miles, you can only fly if it is safe to do so and do not interfere with the manned aircraft (Sgro, 2017) . The worst weather condition to accomplish the mission is stormy and rainy weather. A fail-safe mechanism is considered in the UAS as it is particularly important in risk mitigation. For instance, in case of any failure other than loss of radio connection Ardu-fail-safe can be used. If there is a risk of loss of radio connection Ardupilot will take charge to cut the throttle and vary control surfaces so that the aircraft spirals and lands.
References
Hamilton, O., Bliss, T. and Depperschmidt, C. (2017). Integration of Military Unmanned Aerial Systems (UAS) into the US National Airspace System: The Relationship Between UAS Accidents and Safety Concerns. International Journal of Aviation, Aeronautics, and Aerospace .
Papageorgiou, E. (2016). Value Driven Unmanned Air System Design .
RĂDUCANU, G. and CÎRCIU, I. (2017). UNMANNED AERIAL VEHICLE FUTURE DEVELOPMENT TRENDS. Review of the Air Force Academy , 15(3), pp.105-110.
Sgro, J. (2017). Study of unmanned air vehicle regulations . [Ottawa]: House of Commons.
Thumser, P., Haas, C., Tuhtan, J., Fuentes-Pérez, J. and Toming, G. (2017). RAPTOR-UAV: Real-time particle tracking in rivers using an unmanned aerial vehicle. Earth Surface Processes and Landforms , 42(14), pp.2439-2446.
