The command and control element is the nerve center for the UAS operation. It controls the following tasks:
The command and control element utilizes several subsystems to accomplish its missions. They are:
The most important parts of the command and control element are the Autopilot and the ground control station, as described in the following subsections:
Autopilot is the sub-system that enables partial or fully autonomous flight. A UAV can be operated completely by a remote control, where an operator steers the air vehicle all the time, or a UAV can be flown autonomously, where a pre-programmed path is fully executed from takeoff to landing by the autopilot sub-system without any pilot intervention. Small, light-weight autopilots are readily available and are made by a few manufacturers. Besides guiding the air vehicle throughout the pre-set flight path, the autopilot also executes a “lost link” routine if the UAV loses contact with the ground control station. The lost link procedure guides the UAV to a known waypoint, where contact with the ground control station can again be established. The following scenario was developed for a typical emergency procedure based on loss of link between the Yamaha RMAX UAS and the ground Control Station:
The RMAX utilizes a redundant communication system to ensure constant contact between the aircraft and the remote pilot. The ground control station provides real-time data regarding aircraft location, altitude and flight characteristics. The pilot constantly monitors the flight information provided to the ground control station, and through the assistance of a trained observer, maintains a visual line of sight to the aircraft. In the event of a loss of link between the aircraft and the ground control station, the subsequent procedures are followed:
Problem: | Sign of Problem: | Monitored throughout: | Solution: |
---|---|---|---|
Low Signal | Vehicle is slow to respond to manual commands or PCC commands. Autopilot terminates steering mode. Audible and warning light alarms. | Yes, signal strength displayed in percentage and packet update rate. | Turn Autopilot on and abandon manual flight. Initiate auto-land. |
Loss of Communication | Autopilot terminates manual control or fails to respond to PCC commands. Audible communication alarm and warning light. | Yes. | The vehicle returns to loss communication waypoint, hovers until elapse of flight timer, then commences auto-land procedure. |
Loss of GPS | First indication is poor altitude hold performance, also poor position hold during hover. | Yes, indicated by the number of satellites tracked and GPS Quality PDOP. | Assume manual control of aircraft and land. |
Low Power Avionics | Lower than nominal voltage displayed. | Yes. | Land Immediately. |
Engine Failure | Noise level or RPM changes, engine loses power. | Yes, monitored by rotor RPM through the RPM sensor. | Return and land immediately. If the engine dies, initiate autorotation procedure. |
Tail Rotor Failure | Loss of tail control. | No. | Switch to manual control and initiate autorotation procedure. |
The ground command station (GCS) is the site where the pilot controls the UAV during the flight. The GCS size and sophistication depends on the category of the UAS/UAV. Some large UASs require a formal facility with multiple workstations and personnel, while a GCS for small UAS can be a handheld transmitter. Most UASs used by the geospatial community are small UASs that do not require a dedicated GCS.