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commercially sourced components. There are also two custom-made batteries to provide back-up power, both housed in a box that also contains the main power switch. The first, a 5S-format lithium-iron phosphate battery, is charged and balanced in flight. As well as taking over in case of an alternator failure, it can also be used to power the aircraft during pre-flight checks. The second is a smaller, lithium- polymer pack with its own connection to the power distribution board in the PCM. The power management logic switches over to this in case of a failure of the main battery, its associated circuit board or its power supply cable. The power conditioning circuits, which include voltage regulation and rectification, are Alpha’s own design. Wiring is conventional rather than integrated into the structure, and Alpha makes its own looms using wire and IP67- rated connectors from Binder Industrial, which are fitted with the same kind of abrasion protection that Airbus uses, Escarpenter says. In some places, micro-D connectors are used as they provide high- quality, high-density pinouts. Structure and materials The fuselage’s primary structure consists of a set of carbon fibre-reinforced plastic (CFRP) frames cut from flat plates, some oriented vertically and some horizontally. Other components are directly bolted to the CFRP plates to aircraft-grade aluminium fittings or to isolation mounts. The two vertically oriented frames are bolted together, kept a few centimetres apart by spacers that take the compressive clamping forces from the bolts that pass through them. This forms a rigid spine, to which the horizontal plates that provide platforms for equipment are bolted via fitting blocks. All the nuts and bolts are standard industrial products made from Inox stainless steel. The engine is bolted rigidly to the structure to maintain its positional relationship with the transmission,