Aircraft Special Fasteners

Nut plates are used in areas requiring frequent access, like panels, and are often secured with small rivets and screws. They are designed to float, allowing for slight alignment adjustments. Nut clips, similar to those in cars, offer a flexible and replaceable solution, especially useful when access is limited. Both come in various shapes and sizes, with some nut plates even designed to be glued on. Mechanics frequently replace worn-out nut plates.

Cherry Max rivets are expensive, about a dollar apiece, and are used in places where solid rivets cannot be bucked from the back. They require a special installation tool that pulls a stem, locking it in place with an internal ring, then breaking off. Improper stem breaks (too high or too low) indicate a faulty installation and necessitate replacement. They come in universal head, countersunk, and unisink styles, and are removed by grinding the head, punching out the pin, or carefully drilling, which can be challenging due

Huck bolts, similar in appearance to Cherry Max rivets, also require specialized installation tools. These tools are costly, starting around $1500, with additional heads for different angles costing approximately $500 each. Standard pop rivet guns cannot be used for these fasteners, making their installation and removal a significant investment.

Hi-Loks are a favorite fastener. They are expensive, starting at a dollar each, and come in various materials like titanium and aluminum. Different head colors (orange, black) indicate their material or specific design for tension or shear applications. A grip gauge tool is used to determine the correct Hi-Lok size. They can also come in 'oversize' variants (first, second, or third over) if a hole is accidentally enlarged. Hi-Loks are installed by holding the bolt with an Allen wrench while tightening a specialized nut until it shears off at a precise torque, preventing overtightening.

Hi-Lok collars come in different colors (blue, red, black) each signifying a specific application, such as nominal size or different 'oversize' increments. Steel Hi-Loks are used in high-heat areas like engine compartments. 'Hi-Lights' are a lighter version of Hi-Loks, with one thread removed to reduce weight, contributing to overall aircraft weight savings and increased payload capacity.

Jo-Bolts are fasteners that swell on the backside when installed, clamping down on the material without deforming or smashing composites. They are threaded and pull a washer into place. While effective for composites, they can be difficult to remove.

Cam-Locs and Zeus fasteners are temporary fasteners, not replacements for nut plates, typically found in areas requiring frequent access like engine cowlings. They are prone to spinning if over-torqued and often require replacement due to vibrations and frequent removal. The speaker expresses a strong dislike for working with them due to their common issues.

Removing Cherry Max rivets is difficult because their steel stem makes drilling challenging, as the drill bit tends to stray to the softer aluminum body. For universal head rivets, grinding off the head and punching out the pin is suggested. For countersunk Cherry Max, drilling until the stem can be punched out is often the only option.

Hi-Loks can be removed using pliers, chisels, or specialized cutting tools that fit into a 90-degree drill motor. These cutters shave off the collar, but can break if they hit the steel threaded area or if used on certain collar types. When installing Hi-Loks, the hole should be an interference fit, slightly smaller than the bolt shank. Specialized ratchets and air tools exist for quicker installation, especially in manufacturing settings.

Aircraft bolts are precisely machined with a radius at the head-to-shank transition, unlike standard hardware store bolts that are stamped. This radius prevents shearing at the head. A critical step before installing a Hi-Lok is to lightly countersink or 'relieve' the metal around the hole to accommodate this radius. Failing to do so can cause the part to cut into the bolt's radius, leading to potential shear failure, as demonstrated by a damaged prop bolt.

Taper locks, primarily seen on Boeing aircraft (especially in wings), are bolts that are progressively larger from the thread to the head, ensuring a tight, unmoving fit. They are integral to the aircraft structure, accommodating the wing's compression and tension cycles. Removal is difficult, often involving trial and error to find the correct bolt and requiring an upsized replacement. Cherry buck rivets are bi-metal rivets used in high-stress areas like thresholds; they are hard to install, requiring a large rivet gun, and are not commonly used.