M6.5 Flashcards
How are screw threads measured?
- measured with a screw thread pitch gauge
What are the classes of fit?
Class 1 > loose fit
Class 2 > free fit
Class 3 > medium fit
Class 4 > close fit
Class 5 > tight fit
Generally aircraft screws are manufactured with what class thread fit?
- class 2
Generally aircraft bolts are manufactured with what thread class fit?
- Class 3
When cut in clockwise direction, the thread is said to be?
- right hand
When cut in anti-clockwise, the thread is said to be?
- left hand
What thread should be used for fasteners where locking power is required?
- single lead thread
What are the common thread standards?
- British standard thread forms
- American national thread forms
- unified thread forms
What are the 4 British standard thread forms?
- British standard whitworth
- British standard fine
- British standard pipe
- British association
What are the 2 American national thread forms?
- ANC (American national coarse)
- ANF (American national coarse fine)
What is the angle for American national thread forms?
- 60*
BSW vs BA angle difference ?
BSW - 55*
BA - 47.5*
Does a fine pitch screw have stronger grip than a coarser screw
True
Fine thread = more threads
Coarse thread = less threads
True or False?
True
What is a bolt designed for?
- to hold 2 or more items together
Bolts that are typically used on aircraft structures are what shape?
- Hex heads (range of sizes)
What does AN stand for in terms of bolts?
- army/navy
Aircraft bolts are available in which material?
- cadmium-plated nickel steel
- corrosion resistant steel
- 2024 aluminium alloy
Unless specified, a bolt is made of?
- cadmium plated nickel steel (corrosion resistant bolt)
Clevis bolts are applied when what load is applied?
- Shear
When are eye bolts used?
- when external tensions are to be applied
What are internal wrenching bolts made out of? Also what loads is it designed for?
- high strength steel bolts
- designed for high tensile strengths
What are the 2 basic types of nuts?
- self locking
- non-self locking
What are self locking nuts?
- contain a locking device in the design to prevent it from becoming loose
Nylon self locking nuts must not be used where temp is >121*c (T or F)?
True
What self locking nut is used when temp exceeds 121*c?
- metal lock nuts
Is an engine nut approved for airframe structure?
- false
When is a wing nut used?
- When a part needs to be removed frequently
What is a stud?
- shaft that is threaded at both ends
- where joints have to be broken frequently
- used to replace bolts and screws to prevent damage to tapped holes
Why are Heli-coils used?
- Protect against insertion and removal of bolts and screws
What are the 3 basic classifications of screws in aircraft construction?
- machine screws
- structural screws
- self-tapping screws
What are machine screws?
- used in light structural parts (e.g. fearings)
- thread runs the full length of the shank
What are structural screws?
- made of alloy steel
- heat treated and can be used as structural bolts
What are self tapping screws used for?
- hold thin sheets of metal, plywood or plastic together
- type A has sharp point / type B has blunt point
What is a dowel?
- solid cylindrical rod that is used where precision alignment is required
- made from wood, metal or plastic
What are the 4 types of heads available on self tapping screws?
- Round head
- Truss head
- counter sunk head
- counter sunk oval head
What is a lock washer?
- spring action of washer that creates a friction force
- only used if the joint is not structurally critical
What are the 3 common lock washers?
- spring
- tab
- shakeproof
What are spring washers?
- when tightened, the spring is compressed creating friction which prevents vibration
What are tab washers?
- 2 or more tabs
- 1 bent over component
- 1 bent over flats of nut
- not reusable
What are shakeproof washers?
- sharp edges prevent unscrewing of nut (internal + external)
- they can be reused if teeth are in perfect condition
What is lock wire?
- securing components
- made of stainless steel
- used in critical areas (lot of vibration)
- it prevents the bolts from unscrewing
What are the 3 common quick release fasteners?
- Dzus
- Airloc
- Camloc
What are the benefits of quick release fasteners?
- easy locking and unlocking
- vibration resistant
- reusable
What are circling?
- used for internal + external locking
- used for retaining shafts, seals, bearings etc
A rivet must extend beyond the base material at least x1.5D? (T OR F)
True
What head is 470?
-universal (dome)
What head is 426?
- Countersunk (flat)
What alloys are Hi-Lok bolts made out of?
- titanium
- stainless steel
- steel
- aluminium
How many turns required for quick release fasteners?
1/4 turn
A shakeproof washer has slanting serrations on internal and external circumference? (T OR F)
True
Can nylon self locking nuts be used in engines?
Yes according with engine manufacturer
Aluminium alloy rivets manufactured from 2117 material are identified by?
- small dimple in the centre of the head
