MEA109 Part B Flashcards
Ensure the hardware is approved…
Ensure the hardware is approved by the manufacturer of aircraft/engine/components
Hardware is manufactured to a…
Hardware is manufactured to a specified standard of quality to meet airworthiness requirements
‘…’ aircraft parts …
“Standard” aircraft parts are those items that are manufactured to specifications.
Class 1
Loose fit (easily turned with fingers)/ A commercial wing nut
Class 2
Free fit (screws)/ Most screws
Class 3
Medium fit (bolts)/ Aircraft bolts
Class 4
Close fit (requires a wrench to turn nut)/ Requires a spanner to turn the nut onto the bolt thread
Threads designated by:
Diameter, Number of threads per inch, Thread series, Class.
Bolt
A threaded fastener that can withstand shear loads or tension loads or both.
Three Main Parts:
- Head
- Thread
- Grip (unthreaded portion).
AN
NAS
MS
- AN – Air Force Navy
- NAS – National Aircraft Standard
- MS – Military Standard
Bolt Fit
Required “bolt stress” achieved by correct fit of bolt in the bolt hole and torque applied
Types of bolt fits
Loose fit, Push fit, Tight-drive fit, Interference fit
In the AN bolt hardware code:
Diameter is given in 16th of an inch
Heads Been drilled
What determines grip length
Material thickness determines grip length
Add plain washers to adjust …
Add plain washers to adjust grip length
How many threads are allowed in the bolt hole or allowed to contact the nut?
None
What is the minimum number of washers allowed under the bolt head and under the nut?
A minimum of one
Unless otherwise specified, the torque values given in MD are for …
clean dry threads
Preload on fastener threads determines
Strength of joints
Incorrect preload may result in
Failure of assembled parts
Hex – Head Bolt (AN3 – AN20)
- Suitable for tensile and shear applications
- Made of nickel steel, 2024 aluminium alloy, corrosion
resistant steel and titanium - Cadmium plated steel bolts
Head marked with asterisk or cross
drilled Head Bolt (AN73 – AN81)
- Head drilled in multiple directions to receive safety wire
- Interchangeable with standard hex head bolts
- Head marked with asterisk * or cross +
Close Tolerance Bolt
- Un-plated shank, apply grease on shank prior to
installation - Cannot be substituted by standard AN hex head bolts.
Clevis Bolt
- Head slotted to receive a flat screwdriver
- Most have drilled shank
- Relatively long grip length with short threads
Eye Bolt
- external tension load applications
- Cadmium plated alloy steel material
- Threaded end may or may not be drilled.
Aircraft Nuts
- Internally threaded component, providing a clamping
action in bolted joints - Available as non-self locking or self- locking nuts
- Made from cadmium plated carbon steel,
stainless steel, or anodized 2024T
Non – Self Locking Nuts (AN310 & AN320)
- Castellations (slots) in nut accommodate a cotter pin to
the secure bolt
-
AN310
Thick nut , withstands large tensile loads, also
known as a castle nut
AN320
Thin nut, used only in shear load applications,
also known as a castellated shear nut.
Plain Nut
AN310
- Thick nut, for tension and shear applications
- requires external locking feature e.g. check nut or
spring lock washer
Check nut
AN316
- Thin nut used to lock AN315 plain nut
- Available in left and right hand thread
configurations.
Self Locking Nuts
- Design integrates a locking device
- Two types - nylon and metal
- Do not use on parts subject to rotation
Self Locking Nuts – Elastic Stop (Nyloc)
- Locking action provided by an unthreaded nylon insert
- Not suitable in above 250 °F applications
Self Locking Nuts – Metal Lock Nuts
- Suitable in above 250 °F applications
- Bolt’s end must protrude through the nut
and 1 to 3 threads exposed to be in safety
Shakeproof Lock Washer
- Known also as an internal or external star washers
- Used with bolts whenever the self locking or
castellated type nut is not applicable
Taper Pin
- Designed to take shear loads and prevent any loose
motion or play
-Two Types: Threaded, Plain
Roll Pin
A roll pin is a mechanical fastener that secures the position of two or more parts of a machine relative to each other
Aircraft Screws: Classifications and (4) types
Structural screws, Machine screws, Self-tapping screws.
Torx, Slotted, Phillips, Allen
Structural Screws
- Heat treated steel alloy
- Same shear strength as a bolt of
the same diameter - Structural screws have an unthreaded portion (grip),
same as a bolt.
Machine Screws
- No defined grip –threaded full length
- Manufactured from: Low carbon steel, Brass,
Corrosion - resistant steel, Aluminium alloy
Self – Tapping Screws
- “Type A” has a pointed end
- “Type B” has a blunt end
- Machine self-tapping screws: Roundhead, Countersunk
Rivets
- The most common method of fastening sheet metal
- Solid shank rivets (used in sheet metal), blind rivets
1100 Rivet
Dimple markings on rivet head
2017& 2024 Rivets
- 2024 rivet is stronger and harder than 2017 rivet
Keep 2017 and 2024 rivets refrigerated until ready to be driven.
- Ice Box Rivets
- Refrigeration slows hardening process
Mild Steel Rivet
- Use with corrosion resistant steel parts
- Designated with “F” in rivet code
- No markings on a flat rivet head.
Blind Rivet
- Access available to only one end
of rivet when driven - Limited space for bucking bar
- Mechanical lock, self plugging rivet.
Self – Plugging (Friction Lock) Rivet
Not suitable in vibration prone areas.
Self – Plugging (Mechanical Lock) Rivet
Consists of 3 parts:
• Rivet head with a hollow shank
• Mechanical lock
• Steel stem
- Suitable for vibration prone areas
CamlocTM Fastener
To lock – turn stud clockwise quarter turn
To unlock - turn stud counter- clockwise quarter turn
