LOCKING DEVICES

"LOCKING DEVICES"

When an Aircraft is subjected to vibration and stress it tends to loosen its various parts. to prevent this stress or loads, various of locking  devices are used. some of these listed below.

COTTOR PINS

These are steel or nickel alloy steel pins of different diameter and lengths.

USE : They are used with slotted or castle nuts to lock the bolts or studs.

FITTING :  Align the nearest slot of the nut with the hole provided in the bolt or stud,insert the cotter pin through the slot of the nut and the hole of the bolt,or stud and bend legs of the cotter pin around the nut.

REMOVAL : Straighten the legs of the cotter pin with the help of cotter pin extractor and pull it out from head side.

NOTE : "COTTER PINS ARE USED ONCE ONLY" 

SAFETY WIRES 

Safety wires are made of non-corrosive steel or copper. Different guage of wires are available for use with different sizes of fasteners.

USE : It is use to look nuts,bolts head,oil caps, wheel caps,drain cocks,turn buckles and pipe unions.

FITTING : It differs with components,double twisted method of safety wiring is the most common method used. The wire may be twisted by hand except for the final few twists which should be made with twister. Single wire method may be used on screw in a closely spaced or closed geometrical pattern such as triangle.

REMOVAL : Cut or break the wire and pull in out.

NOTE : "Safety wire is used once only"

TAB WASHERS

Tab washers are available in various sizes and consist of tabs which are used to the nut.

USE : They are used to safety the plain nuts or bolts heads.

FITTING : They are placed under the nuts,once tab in bent into the hole of the structure and the other tabs are bent around the nut.

REMOVAL : Straighten the tabs and remove the nut and tab washers.

NOTE : "TAB WASHERS IS USED ONCE ONLY"

LOCK PLATE

These are thin steel plates with six or twelve sizes to fit around a nut or bolt head.

USE : To lock nuts or bolts.

FITTING : Position the nut or bolt,so that the plate fits around it and lock the plate with set screws and spring washer.

REMOVAL : Removal the set screw remove the plate and remove the nut.

SPRING WASHER

It is under the head of machine screw or with the plain nuts where the self locking or slotted nut is not appropriate. The spring tension will keep the nuts or screws from loosening.

CHECK NUTS

Check nuts are used as locking devices for non self locking plain nuts. They are used to lock the eye ends of a tie rod.

SAFETY PRECAUTIONS

1) The safety wire shall not be used to secure the emergency device such as handle and switch table.

2) When safety wire is used, particular care should be exercised to ensure that it will not prevent emergency operation of the emergency devices.

3) Do not loosen or tighten the properly tightened nut to align with safety wire holes.

4) lock pins and cotter pins should fit snugly in the hole provided.

5) Cotter pin, lock wire and tab washers are used once only.

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