What Are Special Purpose Bolts?
When constructing an aircraft, a plethora of components come together to form the various assemblies and structures that aid the vehicle in attaining flight. To achieve such complex structures that are able to withstand the various forces and stresses exerted on them during flight, highly robust components such as aircraft fasteners are used. Bolts in particular are fasteners that are used generously across aircraft assemblies, and there are various special purpose types that are implemented to fulfill specific needs and loads.
Bolts are a type of externally threaded fastener, meaning that they feature external helical ridges that are designed to mate with corresponding components or aid in affixing two or more components. Bolts typically consist of a long shaft that is threaded on the bottom half, and a shaped head that sits on the opposite side. The shape of the bolt head may vary, and these shapes allow specific tools to be used for more precise amounts of torque application. To install a bolt, the tail end of the component is passed through preformed holes in the assembly, and a correlating nut is tightened from the other side to hold the assembly in place. With the use of nuts, assemblies are held together through the use of compression and axial clamping forces. As aircraft bolts, bolts are most often used where there is a need for a high amount of strength. In regards to special purpose fastener types, the most common special purpose aircraft bolts include the Jo-bolt, lockbolt, clevis bolt, and eye bolt.
The Jo-bolt is a three piece rivet that features internal threading. For installation, the bolt is rotated while the pre-assembled nut is held. Through rotation, the sleeve expands over the end of the nut, causing a blind head to be produced, clamping the fastener in place. When an optimal amount of torque is applied, a part of the bolt breaks off. The advantages of Jo-bolts are their high shear and tensile strength, allowing them to be optimal for high stress applications where a blind fastener is not practical.
The lock bolt is one that provides many of the capabilities of high strength bolts and rivets. These aviation hardware parts are installed in areas such as landing gear fittings, longerons, beams, wing splice fittings, fuel cell fittings, and various other major structural assemblies. As compared to standard rivets, the lockbolt is simple and quick to install, creating a robust and permanent assembly with the use of a pneumatic gun. Unlike many other bolt types, the lockbolt does not require special nuts or lock washers.
The clevis bolt is a type that features a rounded shape, often having slotting or a recessed head so that a typical screwdriver or crosspoint screwdriver may be used to install it. Clevis bolts are entirely used only for accommodating shear loads, and they will never be implemented for tension loads. A common application of the clevis bolt is to be used as a mechanical pin for a control system.
When there are external tension loads that need bearing, special purpose bolts such as the eyebolt are installed. An eye bolt is a bolt that features a head with a loop at one end of the fastener. When installed, the bolt then provides a secure eye to a structure, allowing for ropes and cables to be tied down to it. For the use of aircraft, eye bolts are often used for the attachment of devices such as turnbuckle forks, clevises, and cable shackles. To increase safety of the assembly, the threaded end of the eye bolt may be drilled.
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