To allow flight beyond the line of site of the pilot, or even to automate flight within the pilot’s field of vision, some form of autopilot must be fitted to the aircraft. Generally, this sits between the standard aircraft flight control receiver and the servos that operate the aircraft’s aerodynamic control surfaces and throttle. In manual mode, the autopilot simply passes control signals through unchanged. When some form of autopilot control is required, the unit then substitutes its own servo commands for those coming from the receiver. The autopilot generally also has its own communications channel to a ground control station as well as connections for Pitot tubes and GPS aerials. A range of autopilots are commercially available, some with open-source codes such as those that use the Arduino family of hardware (Figure 6.20) or the
Figure 6.20 Basic Arduino Uno autopilot components including GPS module on extension board, and accelerometer, barometer and three-axis gyro on daughter boards.
Figure 6.21 Pixhawk autopilot.
Pixhawk system (Figure 6.21) and others that use proprietary approaches. The more sophisticated systems are typically subject to export control and can be as expensive as a small UAV in their own right. We mostly use the units developed by SkyCircuits for our most complex aircraft, which we find to be a good compromise between capability, cost, and ease of use, see Figure 6.22. All allow the connection of a range of important sensors such as Pitot tubes, barometric altimeters, and GPS systems.