6.3 composite materials Flashcards
What is a composite material?
Two or more materials combined to form a stronger structure
What two things are a composites made up of?
The matrix
The reinforcing material
What form is the matrix normally in?
Liquid
What form is the reinforcing matter in?
Solid
A third material is often used (such as honeycomb) to do what?
To make it stronger
Where are composites mainly used on an aircraft?
Primary airframe components.
List three advantages of modern day composites?
High strength to weight ratio
Longer service life
Easy repairable
Good corrosion resistance
What type of strength does modern day composites encourage?
Tensile
What are some disadvantages of modern day composites?
Expensive
Lack of methodology
Toxic and hazardous
Lack of knowledge
List the reinforcing fibres
Aramid
Black graphite
Boron
Ceramic
Fibreglass
What are the two different types of fibre glass?
E-class and S glass
How do you make fibreglass?
Heat up glass until it’s molten, then you force it through small holes
This creates what?
Glass filaments
What can glass filaments be used for?
Insulations and cloths
What are the advantages of fibreglass?
Does not conduct electricity
Less expensive
What is another name for Aramid?
Kevlar
What ensures the gold colour does not turn brown on Kevlar?
Protection from the environment
What is Kevlar sensitive to?
UV light
What are the two types of Kevlar used?
49 and 29
When are Aramid reinforced fibres used?
When areas are prone to impact damage
What property effects the ductility of Kevlar?
It has poor compressive strength
When cutting and drilling Kevlar, what’s must you ensure?
Specialist tools are used due to the strong nature of the material
What are advantages of Aramid?
Low density
Flexible
Good chemical resistance
High toughness
Non flammable
What main property is carbon fibre used for?
It’s rigidity and strength
What aircraft components is carbon fibre used on?
Structural components
What strength does carbon fibre specialise in?
Compressive strength
Is carbon fibre strong or brittle?
Brittle
When bonded to aluminium, what can occur in carbon fibre?
Galvanic corrosion
What are the advantages of carbon fibre?
High strength
Low density
Good electrical properties
For sanding, what is used?
For sanding, aluminium-oxide or silicon carbide
Which lasts longer, aluminium oxide or silicon carbide?
Silicon carbide
How do you make Boron?
Applying a small amount of vaporised boron onto thin tungsten or carbon
What is the most common use for Boron?
Repair cracked aluminium parts and panels
What is a disadvantage or Boron?
Very expensive
Can be dangerous when inhaled
What strength is suitable to Boron?
Compressive and tensile
Where are ceramic fibres used?
High temperatures
At what degrees does ceramic retain most of its strength and flexibility
1200
What do they work in combination with?
Metal matrix
What is a warp?
Runs along the length of the fabric
Is the warp or the weft stronger and why?
The warp has higher numbers of threads
What is the weft?
They run perpendicular to the warp fibres
What is the selvedge edge?
Tightly woven edge that runs parallel to the warp threads
What is selvedge edge used for?
To prevent unravelling
How does it prevent unraveling?
Runs parallel to the warp threads
What is the Bias?
The fibre orientation that runs at 45 degrees to the warp threads
What are unidirectional materials?
The major fibre runs in the warp direction
What are bidirectional fibres?
When the fibres run in more than one direction.
What is the sequence for Quasi-isotropic Lay up?
0, -45, 45, 90.
0, -60, 60
What about the orientation of Quasi-isotropic makes the material strong and stiff?
The orientation of the fibres in the lay up are balanced
Do the carbon fibre plies need to be made up of woven fabric or in directional fibres in order to create isotopic materials?
Either
What is an isotopic material?
Physical property with the same value when measured in different directions when combined in a well-designed laminate stack
What is a Mat?
Chopped fibres that are compressed
What are mats used in combination with?
With woven or unidirectional layers of fabric
What are fabric weaves more resistant to?
Fibre breakouts,
De lamination
Damage
Are Mats stronger than unidirectional or bidirectional carbon fibre?
No
What difficulties may you face with plain weaves?
It’s difficult to cover complex shapes
What are the mechanical properties like on a plain weave?
low
What crimp degree does plain weave have?
High
What are the two characteristics of a Twill Weave?
Provides wet out and cover to plain weaves
Flatter and offers higher mechanical properties because of reduced crimp.
What is difficult about a satin weave?
They are difficult to handle
What are satin weaves often used for?
repairs
What are the properties of the Satin Weave?
Flat
Civer well
Facilitate wetting out
What is a Satin Weave?
Modified twill weave with fewer inter sections
What does the strength of a composite rely on?
The strength of the matrix to transfer stress to the reinforcing fibres
Are polyester fibreglass materials high or low in strength?
Low
Resin matrices consist of what two components?
The resin and the hardener
When the resin is curing, what does the hardener act as?
A catalyst
What does curing mean?
A period when the resin can be worked
What are the two general catagories of plastics?
Thermoplastic
Thermosetting
Thermoplastic resins use what to form the plastic to the desired shape?
Heat
Is the thermoplastic material reversible?
Yes because it melts then freezes again
What do thermosets use to cure?
Heat and catalysts
Why do thermosets solidify when heated?
They have low melting points.
Once a thermoset is cured, can the shape be changed
no
What type of plastic resin is used in epoxy resin?
Thermosetting
What are epoxy resins most useful for?
Bonding non porous and dissimilar metals
In which manual must you guide you to use the resins?
The manufactures repair manual
What must be adhered to at times when using an epoxy resin?
Product safety data sheet.
What are Pre Impregnated fabrics?
A fabric that has the correct amount of resin in it
What is the viscosity of epoxy resins and what are the consequences?
High so it can be difficult to mix and work the epoxy resins into the fabrics..
High so it can be difficult to mix and work the epoxy resins into the fabrics..
To eliminate error
Why do pre preg materials produce stronger repairs?
Due to the correct amount of fabric to matrix ratio
Why are pre oreg so expensive?
Because companies sell full rolls. No small quantities.
If pre preg resins are not kept in cold storage what can end up happening?
They start to cure
pIn what conditions can a Pre Preg resin be opened?
Controlled environment and room temperature
When you’re done with a Pre Preg resin what must you ensure?
The bag is sealed and it is put on the freezer
What must be recorded when you take a Pre Preg out of the freezer?
The duration of how long it is out for
What are the two types of fibre reinforced composites?
Laminated and Sandwitch
What do laminate composites consist of?
Two or more layers of reinforcing material bonded in a matrix
What is a sandwitch construction?
When the core is bonded between two fibreglass sheets
What is the main advantage of a sandwich construction?
It has high strength to weight ratio.
What is a core material?
Central member of an assembky
What do core materials achieve when bonded between two faced sheets?
Lightweight and rigidity
What is honey comb like in regards to stiffness and weight?
High stiffness low weight
What are the 5 examples of honeycomb structures?
Aramid
Fibreglass
Kraft paper
Aluminium
Steel
Cerami d
What are the three types of honey comb?
Hexagonal
Over expanded
Flexicore
When are Overexpanded and Fkecicore honeycombs used?
On three dimensional and curved shapes
Why is foam not used on aircraft?
It is heavy and weak
What are the three foams called?
Polystyrene
Polyvinyl Chloride
Polyurethane
What are 3 advantages of plastics?
Lightweight
Economically fabricated
Durable
Impact Resistance
Chemical resistance
The common plastic PEEK can withstand large doses of what?
Radiation
PEEK has resistance against what?
Hydrolysis
Hydrolysis resistance means it can be exposed to what without degrading?
High pressure waters and steam
What is PEEK’s operating temperature?
232 degrees
What are examples of where PEEK is used?
Valve seats and pump gears
What is the marketing name for thermosetting polymide?
Merlin
Thermosetting polymide is used for what?
Structural appliances
What properties does PEEK have?
Good mechanical properties
Good chemical resistance
What are examples of where PEEK is used?
Engine pylons and insulations of threaded bolts, leading edges
What is the marketing term used for Polyamide Imide?
Torlon
What number is Polyamide Imide’s (PAI) mechanical strength?
260
What is Polyamide Imide’s (PAI) resistant to at least room temperature?
Chemicals and radiation
What is Polyamide Imide’s (PAI) used for?
Substitute of metal components eg thrust reverser
What properties regarding fire does Polyamide Imide’s (PAI) have?
It is a flame retardant and does not give off smoke when burning.
Where is Polyamide Imide’s (PAI) used?
Thrust reverser assemblies
What type of plastic is PCTFE?
Flurochemical
What resistance does PCTFE have?
Fire and chemical
What other properties does PCTFE have?
Low moisture absorption
Good electrical properties
What is the temperature application of PCTFE?
-240 to 204 degrees
Where is PCTFE used?
Corrosive environments
What is the market name for PTFE?
Teflon
What type of plastic is PTFE?
Fluorocarbon polymer
Does PTFE have high or low flammability and why?
Low flammability because it’s an electrical insulator
What physical properties does PTFE have?
High tear resistance
Retains properties in aerodynamic conditions
Why are transparent plastics split into 2 sections?
Due to their reactions of heat.
What are the two sections of transparent plastics called?
Thermoplastic
Thermosetting
What are thermoplastic materials?
They soften when heated and harden when cooled
What are thermosetting materials?
Harden when heated and reheating does not allow you to reshape them.
Once thermosetting plastics are cured can they be reshaped?
No
How do stretched acrylics react with Impact?
Well
What are other properties does stretched acrylic have?
Less likely to shatter
Chemical resistance
Doesn’t scratch or craze
What two forms can transparent plastics be manufactured in?
Monolithic
Laminated
What are monolithic plastics?
Single, solid uniform sheets
What are laminated plastics?
Transparent face sheets bonded by clear resin
When identifying plastics what must it be in accordance with?
AMM
What does a part need before it can be used?
A part number
What also must be used before a part can be used?
A serial number
When is identification processing included?
When moulding
How are thermoplastics plastics marked?
With a heated die
When is a heated due not suitable?
On tubular sectiondn
What is used to mark a thermosetting plastic?
Vibro-etching tool or white paint/ink
What is different about transparent plastics in use?
They should be avoided when possible
If a transparent plastic is bonded to a metal frame where should the identification be present?
On the metal frame
Where should you apply identification if necessary on a transparent plastic?
On the inside of the pannel
How should you apply identification if necessary on a transparent plastic?
With stencils or sandblasting
What action should you take if you want to temporarily identify something?
A label must be affixed with masking tape but the label should not directly be on the material.
Why are sealents created?
To fulfil multiple purposes
What are the two forms of sealents?
One part and Two part sealents
What are One Part sealents?
They are created by the manufacturer and are ready for application
What are two part sealents?
They come in separate packaging to prevent curing
What do two part sealents consist of?
Equal amounts of sealing compound and acceleration
What can applications of sealents include?
Sealing fuel tanks and fasteners to prevent corrosion.
Smoothing of the aircraft skin
Skin join
What are different about resins used for laminated things and why?
They are thinner to allow saturation of the reinforcing fibres
What are resins used for?
Bonding things together
What is a specialised form of adhesive?
Film adhesive
What is film adhesive?
Pre blends the resin and the catalyst on a thin film of plastic
How can you slow the resins cure rate?
By putting it in a freezer
What can happen to a resin left out at room temperature?
It can cure
If the curing process slows down, what happens to the shelf life?
It expands
What are adhesive films used for?
Bond patches to a repair area
When working with resins what must be adhered to at all times?
The product safety data sheet
What are the three layers in order?
Release layer
Adhesive layer
Release layer or carrier
What are three examples of manufacturing damage
Anomalies
Microcracking
Delamination
Surface damage
Impact damage
damaged p fastener holes
Why are resin riches problematic?
Because they add weight
When is a resin rich composite not problematic?
When it is non structural
How does a component become resin starved?
If too much resin is bled off during the curing process
If not enough resin was applied during the wet lay-up process
How can you tell if an area is starved?
The fibres show at the surface
Where do delaminations form?
Form on the interface on the individual layers
What can delaminations form from?
Matrix cracks that grow into interlaminar layers or impact damage
How do disbonds form?
From poor adhesion along the bond line leading to delaminations
When can a disband cause catastrophic danger?
When subjected to loads such as shear, tension compression
What does the severity of a disband rely on?
Dimensions
Number at a given point
Location
Loads
How can hole elongation occur?
Due to repeated load cycling
Honey comb structures have a thin sheet which cause problems that are classified into what three groups?
Low resistance to impact
Liquid ingression
Erosion
What properties does honeycomb have?
Stiffness and high strength but bad resistance to operational environment. They are also fragile
How can you detect damage to honeycomb?
Through visual inspection
If damage is not checked in honeycomb what could occur as a result?
Liquid ingression to the core causing further damage
What are composite materials prone to?
Erosion
How is erosion tried to be avoided?
By applying an erosion coating, but this does not protect it fully.
What can happen to the edges of a door panel?
They can erode of exposed to the airstream
What do Fibreglass and Kevlar consist of that oritectd then from lighting strikes?
Aluminium mesh
What can happen to the aluminium mesh at the bolt or screw holes?
Corrosion
What does the corrosion of aluminium mesh around bolt or screw holes interfere with?
Electrical bonding of the pannel and the mesh needs to be removed and replaced to restore it’s full potential
What can affect the strength of a composite material?
Ultraviolet
How is protection against UV ensured?
Uv primers and paints
What does NDT determine?
Airworthiness
What is the first thing that happens when damage is done to a composite structure?
Assess how extensive the damage is
What details the inspection procedure?
The structural repair manual
What is the primary inspection method?
Visual inspection
What are typical types of visual damage?
Scorch
Stain
Dent
Penetration
Abrade
Chip
What can you use for closer inspection?
Magnifying glass, torch and mirrors
What can visual inspections not detect?
Delaminations or disbonding
What is the most common technique to detect delamination or disbonding?
Coin tapping
How do you go about coin tapping?
Tapping the defective area with a solid round disk or a lightweight hammer
How does a well bonded area sound?
Sharp and ringing
How does a defective area sound?
Dull or a thud
What is tsp testing effective on?
Thin sheets, honey comb structures or surfaces of thick laminates
When is coin tapping ineffective?
On layers with more thsnn4 plies
What is used to map out the damage on thin honeycomb sheets?
Coin tapping
In an automated tap test what is used instead of a hammer?
A solenoid
What does a solenoid do?
Produces multiple impacts in one area and the tip of the impacter has a transducer that records the force versus time signal of the impactor.
What is used to calibrate a tap test instrument?
The signal off an unglazed panel
What are ultrasonic inspections best for?
Detecting uneasilly visible damage such as delaminations or voids
What technique does ultrasound use?
Sound wave energy that is used above the audible range
How does an ultrasonic wave work?
A wave is either reflected or absorbed from a defected area which is then picked up by a transducer and converted onto a display on an oscilloscope
What are the four common ultrasound techniques?
Transmission
Pulse echo
Bond tester
Phased array
How are X-rays accomplished?
It records the absorption of rays onto a film sensitive X-ray
What does an X-ray allow you to see?
Variations in the opacity
What is an X-ray not preferred to see?
Delaminations
What must you be protected by when working with X-rays?
A lead shield
What does darkness and lightness mean on an X-ray?
White means higher density
Dark means lower density
What is the basic principle of a Thermograph?
Measuring the surfaces temperature when heat flows through it
What do Thermographic techniques rely on?
Variations of thermal conductivity
How do you know if something is defect free by using a Thermograph?
A non defect object conducts heat more efficiently
How can you judge the quality of the bonds?
By seeing his much heat passes through it
What are examples of defects that affect thermal conductivity?
Water ingress
Disbands
Cracks
Impact damage
Pannel thinning
What inspection is most useful for inspecting thin laminates or defects near the surface?
Thermography
What are dye penetrants used to detect?
Cracks and defects on a metallic surface?
Where must dye penetrants never be used?
On composites
Why must a dye penetrant never be used on a composite structure?
As the wicking acting of the fibres can absorb the penetrant and not allow it to bond correctly
What must happen if an area has been affected by a dye penetrant?
All traces must be removed before any new laters are applied
What is a moisture detector used on?
Sandwich honeycomb structures
What does a Moisture Meter detector measure?
The RF power lost due to the presence of water
Where is the moisture meter used most?
In nose randomes
What are the three categories for classifications of damage?
Negligible
Repairable
Non repairable
what is a cosmetic defect?
A defect on the outer skin that does not involve the structural reinforcing fibres
When does impact damage occur?
When a foreign object strikes the part
What is the most common cause for impact damage?
Careless handling
What is BVID?
Barely Visible Impact damage. It can be present when carelessly mishandling during ground operations
What is delamination?
Separation of fabric layers in a laminate material and can occur with no damage to outer skin
what is Delamination caused as a result of?
Impact damage, moisture on the fabric or lightning
What is a core disbond?
The separation between the skin and the core
What causes a disbond?
Poor adhesion, service loading or impact damage
What is difficult about disbond?
They are tricky to see and NDT methods aren’t always effective
What is the most common form of damage in composites?
Cracks
When do cracks in composites occur?
In manufacturing or service conditions
When is water Ingress most problematic?
In honey comb structures
What can water ingress cause?
Weight gain
Contamination of bond joints
Corrosion in aluminium honeycomb
Why are disbonds created by water ingress dangerous in a honeycomb structure?
As it’ll freeze and melt in flight
How are holes created?
Over torquing of fasteners
Impact damage
Holes drilled in wrong place or size
What can happen when a hole is caused by lightning?
It can burn off the resin leaving bare cloth
What are tiny holes known as?
Pin holes
What can happen if moisture and airflow gets into the core?
Delamination
Why are defects in honeycomb overlooked?
Because they are a lengthy repair and could delay the aircraft’s departure
What type structure do fabric covered aircraft wings have?
truss type `
What are the main lengthwise structures in a wing called?
The spars
What are the spars separated by?
Compression memberrs
What are the Compression members created by?
Steel tuning or heavy wall aluminium alloy tubing
What is the truss held together by?
High strength solid steel wires
Where do the high strength solid steel wires cross?
The bays formed by the compression struts
What are the drag wires?
The wires that extend from the front spar inboard to the rear soar outboard
What is the purpose of the drag wires?
They oppose the forces that drag against the wind and pull it backwards
What are the anti-drag wires used for?
They attach the front spar outboard and the rear board inboard
How do anti drag wires accomplish this?
They oppose any force that tends to move to the tip of the wing forward.
What is an adaptation of the Truss type wing?
The box spar wing
What does a box structure built between the soars do?
Stiffen the spars so they can resist the bending and torsional loads
What is the point of the firmer ribs?
They attach to the spars to give the wing an areodynamic shape
What forces does a built up box spar wing accept?
Torsional and bending loads
What is the most common wood used for aircraft?
Sitka Spruce
Why is Sitka spruce so greatly used?
Because of its strength and its ability to withstand shock. It is also relatively free from defects.
What does solid wood refer to?
Beams or spars which are one piece of wood
What does laminated wood refer to?
layers of wood with the grain running parallel to each other.
What does plywood refer to?
Wood and glue where the grain of each layer placed run at 90 degrees to each other
What does high density material include?
Pre preg or compreg
What are the 5 most common wood types?
Sitka Spruce
Douglas fur
Noble fur
Western Hemlock
Port Oxford White Cedar
Yellow Poplar
Which ones exceed Spruce?
Douglas fur
Noble fur
Western Hemlock
Port Ortford white Cedar
Which wood has slightly less strength compared to Spruce?
Yellow Poplar
Who’s responsibility is it to properly access the wood?
The person carrying out the wooden structure repair
What is essential for someone working on wooden structures.
Familiarity with the quality and condition of wood and the defects.
What must be performed to ensure that the wood quality meets the original specification?
An inspection with the AMM
What are the characteristics that must be followed during a wood assessment?
The way the wood is cut
The way the grains are shaped
The number of annual growth rings
The way the wood has been cut
The slope of the grain
What is the maximum slope of the grain
25mm
How much sawn is aviation wood?
Quarter sawn
Why is aviation wood quartersawn?
To reduce the amount of shrinkage
What degree are the annual growth rings at on quarter sawn wood
90 degrees
How do you calculate the number of rings?
Look at the end of the board and count the number of rings in one inch
What is the maximum grain count for soft wood?
Six rings per inch
What should Yellow Poplar not be used as a substitute for?
spruce
What wood can not be used as a substitute for Spruce?
Yellow Poplar
In what woods do the growth rings run parrallel to the board edges?
Quartersawn and Rift sawn
The growth rings on the front of the face are at what angle to the face of the board on a quartersawn?
60 - 90 degrees
The growth rings in rift sawn are at what angle to the face of the board?
30 - 60 degrees
The growth rings in plain sawn run at what angle to the board face?
30 degrees
Which wood is easy to work with hand tools?
Port Oxford White Cedar
What is the grain deviation of all wood?
1:15
What must wood preservatives be toxic too?
Fungi, pests and marine organisms
What properties must wood preservatives not contain?
Corrosive
What must wood preservatives be free from?
Objectional properties of use and mishandling
How can you keep a wooden structure clean?
With a soft and slightly dampened cloth and then wiped dry. Then a polish is rubbed into the structure
What can moisture, sunlight and temperature cause?
Wood damage
What can wood the subject to?
Rot and mildew
Where must wooden aircraft be kept?
In a well ventilated hanger
How can wood be protected?
With a chemical preservatives
What must application of wood preservatives be in accordance with?
The AMM
What is the purpose of interior finishing?
To protect the wood against moisture change introduced by damp air or water
What do coatings between wood and metal achieve?
Protect the metal from corrosion due to moisture
What is the purpose of exterior finishing?
To protect the wood against weathering, provide a smooth surface in in flight, and provide a suitable appearance`
What must be removed from exterior finishing?
Oil and grease. Also sawdust shavings and chips
Finished repairs of internal members need to have what applied?
A thinned coat of varnish followed by two full coats
What else need to be treated with three layers of varnish?
Built up box spars and closed structures
Due to weather, abrasions and sunlight, which area needs more protection?
Exterior surfaces
At 50 degrees how much strength does wood loose?
25%
Which is more absorbant, end grain or side grain?
End grains because it absorbs moisture
How do bolt holes contribute to moisture?
They allow moisture to enter
What can variations in moisture content around bolt holes lead to?
Decay or splitting
What can excessive moisture at bolt holes lead to?
Corrosion of the bolt holes
How can you prevent damage at bolt holes?
By applying a varnish
What must you ensure about the sealer?
That it has cured before installation of the bolts
What causes a knot in wood?
gere a branch grew from the tree
What are spike knots?
They are cut parallel to the wood
Are knots acceptable to use on an aircraft?
no
What is a pitch pocket?
A small opening in the annual rings of a tree which fill with resin
When are pitch pockets acceptable?
When they are in the centre portion of a beam
How does compression wood originate?
When a tree grows to one side so the annual rings differ
Can compression wood be used in repair?
no
What is a compression failure?
When a tree falls and hits the ground causing the wood fibres to buckle
How is compression failure identified?
By thread lines
What is a split?
A lengthwise separation (caused by the disruption of wood fibres)
What is a split a result of?
A poor drying process
What is a check?
Runs across the annual rings of a board
When is a check established?
During the seasoning proves
What is a shake?
When two annual rings separate along the boundary
Can woods that have shakes, checks or splits be used on aircraft?
no
How do streaks caused by decay appear?
As streaks in the grains as the woods
What indicates decay in the wood?
Uniform discolouration
What is decay caused by?
Fungi that grows on damp wood
How can you prevent decay?
By proper seasoning and storage
Will good wood splinter or come off in chunks when tapped with a knife?
Splinter
What colour is dry rot?
Brown
How is dry rot caused?
Decay by fungi
How does dry rot start?
With moisture
How do you prevent dry rot?
By ensuring that kiln dry wood with a content of 20% moisture is used.
Or use a varnish
what is dry rot?
Brown rot decay caused by fungi, needs minimal moisture.
what is kiln dried wood?
Wood with 20% or less moisture content to prevent dry rot.
what is surface finish?
Varnish or paint to protect wood from dry rot.
What do adhesives and glues ensure?
The finished strength of any structural repair meets the required specifications
What does each type of glue need to do be in accordance with?
The AMM
What are the 4 most common adhesives? (CPRE)
Casein
Plastic
Resorcinol
Epoxy adhesive
What is Casein glue?
Its powdered glue made out of milk
When does Casein glue deteriorate?
When exposed to moisture
Are modern day glues compatible or incompatible to Casein glues?
Incompatible
If a glue that has been glued with Casein needs to be rebonded to something, with a different type of glue, what must you ensure?
There are no traces of Casein glue
Is Casein alkaline or acidic?
Alkaline
What does the alkaline nature of Casein?
It doesn’t allow glue to cure properly
What is the performance of Casein glue classed as?
Low grade so isn’t allowed to be used on an aircraft
What is Urea-formaldehyde also known as?
Plastic resin
Under what conditions can plastic resin deteriorate?
Moisture and warm humid environments
Is plastic resin allowed to be used in aircraft?
No
What is resorcinal glue?
Two part synthetic resin
What are the two parts made up of in a Resorcinal resin?
A resin and a hardener
What feature relating to water does resorcinal glue have?
It has water resistance
Because of its strength and durability requirements, is Resorcinal glue used in aircraft?
Yes
What are epoxy resins?
Two part synthetic resin glues
What does the two parts of epoxy glues consist of?
A resin and a hardener
What do epoxy resins require less of?
Attention to joint quality or clamping pressures
What factors can affect the joints durable in epoxy resins?
Humidity and temperature
What process ensures the structural integrity of a wooden joint?
The bonding process
To form a successful wood joint what do you need to do to the surface?
Prepare it
What does it mean to prepare a surface? (Three things)
Clean
Dry
Free of any oil
What can happen when you fail to clean the surface properly?
Prevent the glue from penetrating the wood
What temperature does a wood joint need to be constant for to equalise the moisture content?
24 hours
How should the wood joint mate to produce a strong and durable bond?
evenly
What must you not use to smooth the surface?
Sandpaper
What can sanding do?
Round off corners and change the flatness of the wood
When applying the adhesive how must you apply it?
Evenly to both surfaces
How can you help the adhesive spread evenly after applied?
By putting pressure on it
What is the strength of the glue dependant on?
The pressure applied
What brings the wood together evenly?
Clamping
What can too little pressure due to the joint?
Weaken the joint
What can too much pressure due to the joint?
Squeeze out the resin also weakening the joint
What is the recommended clamping pressure for soft wood when using resorcinal glue?
862kPa - 1034kPa
What is the recommended clamping pressure for hardwood when using resorcinal glue?
1034kPa - 1379kPa
What is used for a test?
Off cuts of actual components
When testing the wood, how many wood fibres should show over the fractured glue surfaces?
75%
What are the three factors that contribute to decay of wood?
Sunlight, Moisture, Temperature
What two things helps with visual inspection?
A magnifying glass and light
How can you use light to reveal damage?
By shining it across the aircraft skin
What type of damage does shining a light across the aircraft structure show?
Shakes and pockets
What are the 5 types of wood damage?
Bond failure
Finish failure
Stress damage
Wood decay
Splitting or cracking
What objects can you use to take through a visual inspection?
Magnifying glass, torch, mirrors
What two things can a visual inspection be classed as?
External or internal
What can indicate a growing fungi or dampness?
A musty smell
What are the common types of wing spars?
Plain rectangular spar
Box spar,
I spar (double or single)
C section
Router spar
When repairing a wing spar, what should the reinforcing plates be made out of?
Spruce or Plywood
The reinforcing plates must be how much thicker than the spar when repairing a wing spar?
1/4 as thick
The reinforcing plates must extend the crack by how much on a wing spar repair?
3 times the thickness of the wing spar
What mustn’t you use when repairing a wing spar and what must you use instead?
Nails or screws
Glue
What is the taper and thickness you must bevel the ends on a wing spar repair?
5:1 with a 1/8 thickness
Why must you not use nails and screws when repairing a wing spar?
Because it can split the wood
Where can you use nails and screws?
Where pressure is not
Splice repairs are not permitted in what areas?
Landing gears
Engine mount
Struts
Attachment fittings for the wing root
What needs to be done if damage is done to any of the areas that don’t allow a splice repair?
The whole spar needs to be replaced
If a repair is permitted to a wing spar, how many splice repairs can it undergo?
2
When is a spar deemed repairable, and how much should the damage be cleared out too?
When it’s damaged on the top or bottom edge and it should be cleared out to 1/4 of the spar thickness.
When a wing spar damaged area is removed what should the ends be tapered to?
5:1
What repair is used to splice a new section of a spar?
The scarf repair
What is the scarf angle/taper?
1:10 or 1:12
How can you ensure correct alignment on a scarf repair?
By applying equal pressure
On a scarf repair, what must you taper the ends to and why?
2:1 to prevent any sharp changes in the cross sectional area of the repaired spar
On the end of each scarf, the reinforcing plate that is glued on must be how much in thickness?
1/4 of the spar
On a scarf repair much must should the reinforcing spar extend?
6 times the spar thickness
What are wing ribs made out of?
Spruce strips
What is the cross sectional area of Spruce?
6mm to 8mm
What do the small strips accept?
Air from the fabric coverings and they’re transmitted into the wing spars
During the manufacturing process, what is steam used for?
The soften the wood
What form the upper and lower surfaces that attach to the supporting web?
Cap strips
What do the cap strips do?
They carry the bending loads of the wing and provide a surface to attach the wing skin.
If a cap strip is damaged between its upright members, what must you cut the cap strip to?
12 times the thickness
What wood is used as reinforcement?
Spruce
What width and legnth must you cut the cap strip?
16 times its width but the same length
If the damage in a cap strip is located between TWO upright members, with what taper should you cut the strip?
And where must the cut be located?
10:1
Above the upright member
What does the upright member is cap strips serve as?
The reinforcement meaning no block is needed for support
How can you ensurethat no joints depend of end grain gluing?
By putting thin plywood on both sides of the splice
What is the trailing edge common for?
Moisture damage
On a leading edge, what helps with water drainage and ventilation?
Drainage grommets
What is a downside to drainage grommets?
They clog so cause dirt and moisture to collect
What must be referred to in any type of repair?
The AMM
What do plywood skin repairs depend on?
The size of the hole and its location
What are the 5 common types of plywood repairs?
Fabric
Scarf
Plug
Surface
Splayed
A fabric patch repair is best used to repair what?
Small holes in plywood not Exceeding 2.5cm
Before applying a fabric patch repair, what must you ensure about the hole’s edges?
They are sealed with a two part epoxy resin
What are the advantages and disadvantages of the varnish used on the edges of a hole?
They have a long cure time, but they provide the best seal on wood
The fabric used must be approved by what?
The cement from the manufacturer or the fabric system
What can you use to cut the fabric?
Pinking shears
How much must you overlap the plywood skin in a fabric patch repair?
2.5cm
Where must a fabric patch not be used?
In a leading edge, front fuselage or nearer than 2.5cm to any frame member
What is a aged patch?
A flush patch
On a splayed patch repair, what are the edges tapered to?
5:1 to the thickness of the skin
When is a splayed patch repair used?
When a hole is not more than 15 times the skin thickness and the skin is not more than 1/4 thick
What can a splayed patch repair not be larger than?
3.8cm trimmed hole on thin plywood
When can a plywood skins be repaired with a surface or overlay patch?
When it’s not over 0.3cm between framing members.
When are surface patches permissible?
Aft 10% of Chord line
The radius if the corners must be how much of the skins thickness?
5 times
What must the doublers be strengthened by?
Saddle gussets
What should the leading edge of the patch be bevelled to?
4:1 of the skin thickness
What are used to apply pressure to a surface patch?
weights
The patch should be covered with fabric that overlaps the original structure by what?
5cm
What is the principle of a plug patch repair?
To cut out a damaged area and replace it with something the same size
A plug repair is skin only, so what does this mean for repairs in general?
It can’t be used in damage that involves the supporting structures underneath the skin
What is a plug patch repair held in place by?
A doubler
What do the scarf repairs have the sloped bevelled at?
1:12
In terms of thickness when can a scarf patch be installed?
When the radius of curvature it is not more than 100x times the thickness
What must you do prior to emplaning the patch?
Steam or soak the patch to preform it
What type of surfaces are not recommended in scarf patch repairs?
Sawn or roughly filed surfaces as they are inaccurate and do not form the best glue joint
What are the two types of scarf repairs?
When the back is non accessible
When the back is accessible
What is a warp?
The warp threads run the length of the fabric as it comes off the roll
Are there more threads in the war or fill direction?
The warp
Which is stronger the warp or the fill?
The warp
What is the fill?
The fill runs perpendicular (90 degrees) to the warp fibres
What is the selvedge edge?
Tightly woven edge that runs parallel to the warp direction
What must happen to the selvedge edge before the fabric is used?
It must be removed
What is the bias?
It runs at 45 degrees to the warp threads
Fabrics had a tendency to sag to the left, so what action did manufactures take to prevent this?
They varnished it in oils and varnished
In 1916 what was mixed together to coat aircraft fabrics?
Cellulose dissolved in nitrate acid ti create nitrate dope
What does the nitrate acid ensure?
The fabric is stiff and tight which makes it airtight and waterproof
What does nitrate dope ensure about the finish?
That it’s smooth and durable
What is the biggest disadvantage to nitrate dope?
It’s flammable
to address the flammability issue, what did manufacturers do?
Mix cellulose in butyric (butyruc dope)
What does butyric dope protect the fabric from?
Moisture and dirt but does not adhere as well as nitrate dope
What did nitrate dope and butyric acid not address?
Deterioration caused by UV lights
How did protection to UV rays come about?
Aluminium solids were added to the butyric coatings to reflect the suns rays
What is bad about aircraft dope?
It is toxic
What must you read before using aircraft dope?
The Safety data sheet
Where must you only apply aircraft dope?
In a well ventilated area
What is cotton and linen’s service life like?
Short because of biological effects
What is the cost like for linen and cotton?
It is cost effective
How are polyester fibre materials fitted?
By pre sewen covering envelopes or adhesives
How is a good fit polyeter fibre material fitted?
Through ironing
When does Polyester fabric deteriorate and how can you stop it?
When exposed to UV light
By applying approved coatings
What is polyester fabrics sensitivity like?
It is less sensitive to elements than natural fabrics
Where and how are glass fibres fitted?
On the main plane and tail plane in a span wide direction
What is glass fibres sensitivity like?
It is less sensitive to elements than natural fabrics
What are linen tapes used for?
For covering leading and trailing edges, ribs and repair works
What is special about linen tapes?
The materials are supplied with serrated edges
What temperature must fabric coverings have to stored at?
20 degrees in dry clean conditions away from sunlight
What does the rate of deterioration depend on?
The type of operation
Climate
Storage conditions
Surface finish
When is a visual inspection needed?
Where fretting, oil contamination, wear and water soaking are likely to occur
What must occur for an aircraft to retain its Airworthines
s certificate?
Periodic checks
Which testing devices are not approved and only used for judgment?
The ones you press against or pierce the material
What fabric test devices are used for cotton and linen?
Seyboth and Maule
Why are Maule devices calibrated?
So the fabric can withstand the pressure
What does it mean If the Maule punch tester does not pierce the fabric?
It’s airworthy
Where should the punch test be conducted?
On exposed fabric where there is a crack or chip in the coatings
What must happen if there is no crack or chip in the coatings to conduct a test?
Coatings should be removed to expose the fabric
How do you know if a fabric needs further testing?
The tester tool punctures or bends the fabric
What does the punch test accuracy depend on?
Device calibration, total coating thickness, brittleness and types of coatings or fabrics
What is the difference between a Maule punch tester and a Seyboth punch tester?
The seyboth tester judged off of holes whereas the Maule punch tester aims only to bend the fabric
How is extensive damage in fabric repaired?
By replacing complete fabric panels
When repairing a cut or tear, when is sewing thread used?
When a fabric seam must be made with no structure behind it
What threads are used in polyester fabrics?
Polyester threads
Different threads are specified depending on what?
Hand or machine sewing
When is a Herringbone stitch used?
When repairing cuts or tears that have a sound edge
What is the Herringbone stitch also known as?
The ladder or baseball stitch
When is a wood frame used?
When a cut or tear with a jagged edge cannot be stitched
When is a repair by darning used?
Irregular holes or jagged tears in the fabric
Under what measurements can a repair by darning be used?
Provided the hole is not more than 2 inches or 50mm wide
When is a repair by insertion used?
For damage over 100mm square
What is different about an alternative insertion repair?
The edges of the insertion patch and the aperture are turned upwards
How is the Alternative insert patch attached to the fabric cover?
Stitch along the folded up edges as near to th contour of the component. The edges are then doped down and the repair is covered with a doled on fabric patch
What stitch is used in an alternative insert patch?
Boot stitch
When would re cover be needed?
When the damage is too extensive so the whole surface needs recovering
Why would a re cover be needed?
When a fabric has been damaged by UV rays or if a fabric is too loose.
What is the safe life of a fabric?
5-10 years
What does the rate of deterioration depend on?
Humidity
Type of operation
Storage conditions
Is deterioration uniform?
No
Why do fabrics need to be checked periodically?
For renewal of the airworthiness certificate
How should the fabric sit on the aircraft?
Taut with no loose or wrinkled areas
Why must the fabric tension not be excessive?
Because it can become warped or damaged
How do you measure fabric tension?
Observation
Is Fabric finished with dope that ripples, or is depressed excessively during flight acceptable?
No
How can fabrics that are exposed through cracks in the surface be checked for deterioration?
By pressing your thumb to check the fabrics strength
What deteriorated when exposed to UV, Mildew, moisture, rain, dew, fog, pollution and age?
Natural fibres
What will allow any exposed fabric to deteriorate?
Cracks in the dope
How should cracks in the dope be closed?
By sealing or taking off the coatings and replacing them with new ones
Under what condition does polyester fibre deteriorate?
UV radiation
When is a fabrics service life infinite?
When an approved coating protects the fabric
What must you ensure when covering a component?
You leave access for inspection
What removes condensation from lower ends of fabric components through ventilation?
Drain holes
