Quick-Release Fasteners

Special fasteners have been designed to hold fairings, cowlings and inspection panels in position and to allow their rapid removal and replacement during servicing.

Dzus Fasteners

Cowling and other inspection access doors will usually be found with Dzus fasteners that can be locked and unlocked by a quarter turn of the stud (refer to figure below).

These fasteners consist of a hard spring-steel wire, which is riveted across an opening on a fixed part of the airframe. The stud is mounted onto the panel (or removable part) using a metal grommet.

When the panel is closed, a quarter turn of the stud pulls the wire into the curved slot of the stud, securing the panel to the airframe. Panels (and cowlings) usually have a number of fasteners installed to ensure full security and to indicate that all fasteners are correctly secured, the cowling will have a series of lines marked (painted) on the surface.

When the studs are correctly fastened, then their screwdriver slots will be in-line with the lines marked on the surface of the panels. Some Dzus fasteners have a built-in receptacle, which guides the legs of the stud onto the wire to facilitate correct engagement.

FIGURE

Oddie Fasteners

Oddie fasteners (refer to figure below) have a central stud, which is held in position in the panel with a rubber washer or a coiled spring. A two-legged clip is fastened to the fixed component (usually with rivets). The stud is bullet-shaped and has two recesses opposite each other at the joint end.

The fastener is locked by positioning the recess in line with the legs of the spring and then pressing the stud home. This is achieved by ensuring the screwdriver slot is in line with marks on the panel. There should be a definite click as the fastener engages. A quarter turn of the stud will release it from the spring and free the panel.

FIGURE

Camloc Fasteners

Camloc fasteners (refer to figure below) consist of a spring-loaded stud assembly and a receptacle. The stud assembly is fastened to the removable panel, whilst the receptacle is fastened to the airframe.

To lock the fastener, the stud is pushed against its spring with a screwdriver and given a quarter of a turn clock-wise. As a result, the cross-pin on the stud rides up a cam in the receptacle and draws the two components together.

Finally the stud spring pulls the cross pin into a locking groove at the end of the cam. The fastener is unlocked by a quarter turn anti-clockwise when the stud spring causes the stud to snap outwards.

FIGURE

Airloc Fasteners

Airloc fasteners (refer to figure below) consist of a stud with a cross-pin in the removable cowling or door and a sheet spring-steel receptacle in the structure. The fastener is locked by turning the stud through a quarter turn. The pin drops into an indentation in the receptacle and holds the fastener locked.

FIGURE

Pip-Pins

Quick-release ‘Pip-pins’ are used in assemblies where it is necessary to rapidly remove or reposition components. They usually take the place of more permanent bolts.

The ‘pip-pin’ quick-release fastener (refer to figure below) operates on a push-pull principle. It consists of a hollow body containing a spring-loaded plunger. When the pin is pushed into a hole, two steel locking balls held in the shank of the pin move into a recess in the plunger.

When the pin is fully home and the pushing pressure is released, the balls are forced to protrude from the shank, as the spring around the plunger expands and so lock the pin in position.

A pip-pin is removed by a simple pull on the ring. This action aligns the groove in the plunger with the two locking balls that retract to allow the pin to be withdrawn.

Pip-pins will be found in many places where two components have to be separated at regular intervals and also require a hinging action. An example of where pip-pins would be required is on engine cowlings. These have to be opened daily to allow for engine inspection and are removed completely for engine changes.

FIGURE

Circlips and Locking Rings

Circlips and locking rings (refer to figure below) are manufactured from spring sheet metal or spring steel wire. They may also be specially designed for a particular purpose. Hardened and tempered to give either and ‘inward’ or ‘outward’ spring, they can be used for locking several parts together, locating components within bores or for locating components onto shafts.

Spring sheet circlips have holes in the ends to allow circlip pliers to be inserted, enabling the circlip to be removed or installed as required. Spring wire rings usually have one bent end that is inserted into a radial hole drilled through the component, which matches an inner or outer ring. All circlips are subject to some damage at times and it will usually be a requirement after they have been removed, to inspect them thoroughly. Any that show damage or corrosion should be discarded, although it is usual practice to discard the wire type circlips whenever they are removed.

FIGURE

Keys and Keyways

These items can be found where chain-wheels or pulleys are located on shafts. A key with its associated keyways (the name given to the channel, which is cut into the respective components, to receive the key) is used to transmit the driving force from one part to the other. There are different types of keys and keyways and these will be covered in greater depth in the section on transmissions.

Peening

Peening is a method of preventing a threaded device (bolt, nut or screw) becoming loose by distorting the end of the thread, after installing the device. The distortion is normally achieved (using a centre punch) by striking the thread of the bolt or screw where it emerges from the threaded device, thus jamming and effectively locking the threaded device and preventing it from loosening.

When using a nut and bolt combination, then one and a half threads of the bolt must protrude from the nut in order to create an effective peening.

The disadvantage of peening (and the distortion of the thread) means that once the joint is dismantled, then the threaded device is useless and can only be discarded.