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M6 > 6.3 > Flashcards

6.3 Flashcards

1
Q

What is the definition of a composite.

A

Two or more materials that are combined to form a much stronger structure than either material by itself.

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2
Q

Disadvantages of composites.

A

Inspection methods are difficult to conduct

Lack of long-term design database

High cost in production and repair

Very expensive processing equipment

General lack of repair knowledge and expertise

Products + materials are often toxic and hazardous

Lack of standardised methodology for construction and repairs.

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3
Q

Advantages of composites

A

Corrosion resistant

High strength to weight ratio

Longer life span

Fibre-to-fibre transfer of stress allowed by chemical bonding

Bonded constructions eliminates need for bolts and fasteners

Tensile strength 4-6 times more then steel or aluminium

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4
Q

Fibreglass

A

Most widely used in the industry

E-glass (electrically resistant)
S-glass (strong)
Does not conduct electricity

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5
Q

Aramid fibre (kevlar)

A

Two most common types in aviation:
- kevlar 49
- kevlar 29
Resistant to impact damage.
Sensitive to UV light turns it from yellow to brown.
Complex construction and maintenance.

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6
Q

Carbon fibre / black graphite

A

Used on primary aircraft structures (e.g. Ribs and floorboards)

Stronger compressive strength than kevlar, but more brittle.

Wears out tools

Corrosive when bonded with aluminium.

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7
Q

Boron fibres

A

Very hard wearing
More used on military aircraft
Repair of cracked aluminium
Apply boron vapour to tungsten
Corrosion resistant

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8
Q

Ceramic fibres

A

Used when high temperature applications are needed

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9
Q

Fabric orientation

A

Warp - runs along the length of the fabric
Weft - runs perpendicular to the warp

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10
Q

Selvedge edge

A

Tightly woven edge that runs parallel to the warp

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11
Q

Quasi-isotropic lay up

A

Orientation of fibres are balanced resulting in constant stress and stiffness

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12
Q

Mats

A

Chopped fibres, compressed together.
Not as strong.
Not common in aviation

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13
Q

Plain weave

A

Over under … etc
Lowest mechanical properties
Difficult to cover complex shapes

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14
Q

Twill weave

A

Superior wetout
The preferred weave
Superior mechanical properties (strongest)
Flatter

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15
Q

Satin weave

A

Often used for repairs.

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16
Q

Resin matrix

A

Transfers stress to the reinforcing fibres.
Consists of resin and hardener.
Two types
- thermosetting
- thermoplastics

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17
Q

Epoxy resins

A

Aviation use thermosetting
The MSDS sheets must always be referred to

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18
Q

Pre-impregnated fabrics

A

Fabrics already saturated with correct amount of resin.
Expensive
Stored in a freezer
Short shelf life / out of freezer time.

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19
Q

Laminated composites

A

Two or more layers of re-informing material bonded together and embedded in a resin matrix.

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20
Q

Sandwich composites

A

Core bonded between two fibreglass sheets.
Used in flying control surfaces.
Stronger then laminate

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21
Q

Core materials (sandwich)

A

Honeycomb
- aramid paper
- high strength to weight ratio

Foam
- found in smaller aircraft
- styrofoam

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22
Q

PEEK

A

Poly-ether-ether-ketone
- valve seats, pump gears

23
Q

Thermosetting polyamide

A

A good insulator

Excellent mechanical properties, high chemical resistance

24
Q

PCTFE (Teflon)

A

Fire + chemical resistant
Low moisture absorption

25
Q

PTFE

A

Good insulator

26
Q

Two types of transparent plastics

A

Monolithic (one layer)

Laminated (multiple layers)
- polyvinyl butyral (PVB) forms the inner layer.

27
Q

Marking of thermoplastics

A

Heated dye

28
Q

Sealants

A

Either one part or two part.

Used for fuel tanks, skin joins, aerodynamic smoother.

29
Q

Defects in composites during manufacturing process

A

Micro-cracking, porosity, improper curing, improper drilling, impact damage, delamination.

30
Q

Disadvantages of visual inspection of composites.

A

Damage is often not visible BVID

Visual inspections are often overlooked by engineers who are under pressure to dispatch the plane timely.

31
Q

Effect of moisture on composites

A

Can worsen cracking as water freezes repeatedly.

Moisture ingress ion in the core can lead to skin to core bonding degradation, affecting structural integrity.

32
Q

List the types of non-destructive testing/inspection of composites.

A

Tap testing, ultrasonic inspection, radiography inspection, thermography, dye penetrants, moisture detector.

33
Q

Types of damage in composites.

A

Negligible, repairable, non-repairable.

34
Q

List the 5 basic types of composite repair

A
  • pre-cured patch
  • potted
  • resin injection
  • laminate repair (one surface)
  • laminate repair (through part)
35
Q

Safety precautions when working with composites.

A

MSDS
PPE
Fire protection
Ventilated areas

36
Q

Detection and determination of plastics.

A

Crazing
Cracking

37
Q

Components of a truss type wing

A

Front spar
Drag and anti drag cables
Box structure and box spar

38
Q

List the wood used for aircraft in order of most desirable to least desirable

A

Sitka spruce
Douglas fir
Noble fir
Western hemlock

39
Q

Acceptable slope of grain for aviation wood

A

1 in 15

40
Q

Factors assessed in aviation wood

A

Way it is cut
Shape of grain
No. Of growth rings
Slope of grain

41
Q

How is aviation wood cut

A

It is quartersawn

42
Q

Types of defects in wood

A

Knots
Pitch pocket
Compression
Dry rot
Stained wood
Grain deviation

43
Q

Casein glue

A

No longer used, low grade and obsolete

Needs to be fully removed before applying modern adhesive

44
Q

Bonding process for wood glue

A

Wood must be clean
Not sanded
Dry
Correct pressure in clamps

45
Q

Inspection of wooden structures

A

Sniff test
Tap test
Remove screws and check for corrosion
Check for elongation in joints
Visual inspection
- use a light and a mirror

46
Q

Repairing of wood

A

Reinforcing plates
- 1/4 as thick as the beam
- no more than 2 to a spar
- not permitted in some load bearing areas
- landing gear, wing root, engine mount

47
Q

Plywood skin repair

A

Holes up to 1 inch

Fabric overlapping by 1 inch

48
Q

In which direction can a fabric be stretched

A

Along the bias

49
Q

Dopes

A

Nitrate
- flammable

Butyrate
- sensitive to UV light
- so added aluminium

50
Q

Inspection methods of fabrics

A

Wood frames
Zip panels
Spring panels

Seyboth (punch tester)
Maule tester

51
Q

How long is the lifespan of fabric and give the factors affecting this

A

5-10 years

Climate
Type of operation
Cyclic contraction + expansion

52
Q

Repairing fabric

A

Herringbone stitch
Woods frame
Darning
Insertion
Boot stitch

53
Q

Repairing fabric

A

Herringbone stitch
Woods frame
Darning
Insertion
Boot stitch

54
Q

Components of a truss type wing

A

Front and rear spar which are the main spa wise members.

Compression struts made of alloy tubes.

Drag and anti drag wires

M6 (10 decks)

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