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30 so the major electronic and electrical modules that are sensitive to vibration are bolted to rafts attached to the structural plates via polymeric isolation mounts. These modules include the autopilot immediately behind the transmission, the PCM, the switch box and the payload. The payload bay is the furthest forward piece of primary structure, and takes the form of a ring on one of the main horizontal frames. The payload itself is bolted to a second ring that also acts as an adapter and is attached above the first ring via vibration isolation mounts. While most of the structure is CFRP, some GRP is used to provide the right balance of strength and flexibility, for example in the three landing gear legs. The two forward legs and the single rear leg have a ladder structure. The tail boom is a tube made from aircraft-grade 2024 aluminium alloy with a black finish supported in an aluminium block bolted between the two vertical frames. It is braced by a pair of tubes bolted to a ring about halfway along the boom, and to the lower fuselage horizontal frame immediately aft and outboard of the fuel tanks. Alpha chose aluminium alloy for the tail boom, Escarpenter says, to avoid any problems with static electricity, while accepting a tiny weight penalty (less than 10 g). With the polymer belts running over metal pulleys mounted in a CFRP tube, you would effectively have a Van de Graaff generator! Also fixed to the tail boom by a clamping ring are a GPS antenna and the tail rotor servo on a CFRP plate, which is also bolted to the upper end of the tail skid. That adds rigidity to its connection with the machined end fitting that houses the tail rotor-driven pulley and supports the pitch change mechanism. All materials and fasteners come from suppliers local to the Madrid-based company. Autopilot and navigation UAV Navigation supplies its Vector autopilot, which Escarpenter points out has also been used to convert manned aircraft for unmanned operation and has proved very dependable. It provides full pre-programmed autonomy from take-off to landing, and is integrated with the engine ECU within the PCM. Engine telemetry is available in the ground control station (GCS). Various levels of redundancy are offered for the flight control system, the simplest being what Escarpenter terms “single-sensor fault-tolerant”, meaning that the vehicle will continue to operate safely in the event of a failure in one of the sensors. The Vector features an integrated Polar multi-sensor navigation and positioning system that contains a set of MEMS technology sensors configured into an attitude and heading reference system, an inertial measurement unit, an inertial navigation system, an air data system and a GPS receiver. UAV Navigation says its multi-sensor processing software allows the Polar to suffer the failure of any one of the sensors, and several combinations of them, and still maintain accurate estimates of attitude and position. Escarpenter notes that the Vector is fairly simple in configuration terms, which limits the freedom of platform developers June/July 2018 | Unmanned Systems Technology The switch box (in white) is bolted to an isolated mount on the frame’s upper plate. Beneath it is the autopilot (Author’s image) The autopilot is a system that has been used to convert manned aircraft to unmanned operation, but offers limited configurability (Courtesy of Alpha)