Conformal clearance fit fastener, fastener system, and method for composite structures

A fastener system for providing improved electrical contact with a composite structure, the fastener system comprising:

• one or more fasteners configured for installation in one or more corresponding fastener holes formed in the composite structure, each fastener comprising:
• an elongated shaft having a first end with a head portion, a second end with a threaded portion, and a shaft body disposed between the first end and the second end;
• at least one inner central feed channel extending from an opening in the head portion, through the head portion and the shaft body, along a longitudinal central axis of the elongated shaft, and terminating proximal to the threaded portion;
• a plurality of flutes formed along and circumferentially spaced around an outer surface of the shaft body and an outer surface of the head portion, each flute extending from a first location proximal to the threaded portion, along the outer surface of the shaft body, and radially outward along the outer surface of the head portion;
• and
• one or more lateral feed channels formed laterally through the shaft body, each lateral feed channel connecting the inner central feed channel to at least two opposing flutes on the outer surface of the shaft body;
• an injection tool assembly configured for coupling to each of the one or more fasteners installed in the one or more corresponding fastener holes;
• and
• a conductive fluid injected via the injection tool assembly into each fastener installed in the composite structure, the conductive fluid transported and deposited via the at least one inner central feed channel, the one or more lateral feed channels, and the plurality of flutes of each fastener, to one or more areas between an outer surface of the fastener and an inner surface of a corresponding fastener hole of the composite structure,
• wherein the conductive fluid provides electrical contact between carbon fibers of the composite structure and the one or more fasteners installed in the one or more corresponding fastener holes of the composite structure, resulting in the fastener system providing electrical contact with the composite structure.

A method for providing to a composite structure of an aircraft improved electrical conductivity and dissipation of current energy resulting from lightning strikes to the aircraft, the method comprising the steps of:

• installing one or more fasteners into one or more corresponding fastener holes formed in the composite structure, each fastener comprising:
• an elongated shaft having a first end with a head portion, a second end with a threaded portion, and a shaft body disposed therebetween;
• at least one inner feed channel extending from an opening in the head portion, through the head portion and the shaft body, along a longitudinal central axis of the elongated shaft, and terminating proximal to the threaded portion;
• a plurality of flutes formed along and circumferentially spaced around an outer surface of the shaft body and an outer surface of the head portion, each flute extending from a first location proximal to the threaded portion, along the outer surface of the shaft body, and radially outward along the outer surface of the head portion;
• and
• one or more lateral feed channels formed laterally through the shaft body, each lateral feed channel connecting the inner feed channel to at least two opposing flutes on the outer surface of the shaft body;
• torquing the one or more fasteners in place in the one or more corresponding fastener holes;
• injecting, under pressure, a conductive fluid into the opening in the head portion of each fastener, and through the at least one inner feed channel and through at least one of the one or more lateral feed channels;
• depositing the conductive fluid to one or more areas between an outer surface of each fastener and an inner surface of each corresponding fastener hole of the composite structure;
• curing the composite structure with the one or more fasteners installed in the composite structure;
• and
• providing electrical contact between carbon fibers of the composite structure and each fastener installed in each corresponding fastener hole, to obtain electrical conductivity and dissipation of current energy, resulting from lightning strikes to the aircraft.