Fabrics Flashcards
When would you use light cotton fabric?
To cover a wooden surface
What does tape prevent with fabrics?
Prevents chafing between the structure and the fabric
When is tape also used?
It is also used externally to protect the fabric against damage by the stringing cord
What do the type of threads depend on?
The different job of the material
What sort of material is usually used for stringing?
Flax/nylon cords
How should you store all fabrics used for covering?
Should be stored in a dry, clean environment, away from sunlight and at a temperature of about 20 degrees C
What can you do to prevent chaffing from sharp edges, bolts and screws?
Cover them
What can be used to prevent dope from reacting with protective coverings?
Adhesive cellulose aluminium tape or dope resistant paint
What should you do to internal controls and cables?
Tighten and assume normal positions and secure at the root rib
Why must locations be noted after tightening internal controls and cables?
So that the stringing pitch can be selected to avoid chaffing and interference
What are the 2 methods used for fabric coverings?
Prefabricated envelopes
Blanket method
What is the prefabricated envelope method?
Envelopes that are made loose enough to facilitate slipping them over the structure to achieve the proper tautness after doping
What is the blanket method?
a length of fabric or fabrics joined side-by-side and used to cover the aircraft structure
What are the 2 machined seams used for aircraft?
Balloon (french fell) seam
Lap seam
Describe the process of the balloon seam
edges of the fabric are folded back and are then fitted into each other as shown, tacked together and then machine sewn
When should a lap seam be used?
Only when specified by the manufacturer
What covers the edges of a lap seam?
A serrated strip
Edges are serrated with pinking shears
What is the overhand stitch otherwise known as?
Trailing edge stitch
When is an overhand stitch used?
When sudden changes of sections occur such as
Trailing edges
Wing tips
Wing root ends
What must be allowed when using the overhand stitch method?
Excess fabric so it can be turned under before sewing
How many stitches per cm must be done in an overhand stitch and when should a locking stitch be placed?
3 stitches per cm
Locking stitch ever 50cm
What should use when using threads and cords, that have not been pre waxed, for hand sewing and stringing?
a liberal coating of Beeswax
What does a coating of beeswax do to thread and cords?
Prevents damage in the fabric (holes) , assists in sewing and protects the thread used
What cord is usually used for stringing purposes?
Flax cords
What sort of flax cord is usually used unless the repair scheme dictates otherwise?
Single strand flax cord
Where on an aircraft is boom stringing found?
Deep Aerofoil sections
How does boom stringing differ from typical stringing methods?
The cord is passed around the rib boom instead of around the entire rib
What is the slipstream area?
It is considered to be the diameter of the propeller plus one rib on either side
What are the methods used for fabric attachment?
Adhesives and dope
What sort of aircraft are adhesives and dopes used on and where?
Light aircraft
Wings and tail planes
On what material is dope most commonly used?
Wood structures and occasionally used on metal surfaces
What are other methods of fabric attachment?
Attachment by strip and special stringing
Where are drainage holes placed?
On lower surfaces of components or the places where moisture entrapment is possible
What are drainage eyelets?
Usually oval or circular shape and are doped onto the surface of the fabric, or are secured by stitching pre pierced holes in the eyelets before the finishing scheme is applied
What is shielded eyelets?
Sometimes used in special positions to improve damage or ventilation.
What are the three methods commonly used to inspect panels?
Wood frames
Zip panels
Spring panels
What is a disadvantage of using the wood frame method?
A new patch must be doped on after each inspection and finishing scheme applied
What are the examples of fabric repair methods?
Herring bone stitch
Woods frame repair
Repair by darning
Insert repair
What is the herring bone stitch?
It repairs straight tears and cuts which have more sound edges
After repair the stitching is covered with a doped patch
What is woods frame repair?
Repairs cuts with jagged edges
What is daring?
Used to repair irregular holes smaller than 2 inches wide
The stitching should follow the lines of the warp and weft and the whole repair should be covered with a serrated fabric patch
What is insert repair ?
Repairs holes over the size of 4 inches
What are the two types of fabric tests?
Seyboth test
Maule test
What is the seyboth test?
Seyboth test uses a penetrating cone and a plunger that is pushed down until it pentrates the surface of the fabric. It is marked by coloured bands or a graduated colour scale
What is the maule test?
The maule test uses a spring loaded instrument with a blunt tip and a calibrated scale. It is pushed down on the fabric until the laid down breaking point of the fabric is registered on the scale.
If the fabric has been puncture it fails
What advantage does man made fabrics have to natural fabrics?
Man made fabrics last longer and are less susceptible to damage
What are the two main man made fabrics used in aircraft?
Polyester fibre
Fibreglass
What damages could natural fibres be susceptible to?
Sunlight
Fungal growth
Pollution
What are examples of natural fibres?
Cotton
Linen
What does the dope film do?
Increases tautness of natural fabrics
Waterproofing
Airproofing
Lightproofing
What is tautening?
To tighten
What are the two types if dope used?
Cellulose nitrate
Cellulose acetate butyrate (CAB)
What cant cellulose nitrate be used on?
Glass fibres
What is a disadvantage of nitrate dope?
It is highly flammable
What is a solution to the solvents in dope that attack the paint and soften it?
Dope proof paint
What is dope proof paint?
Used to coat the structure which will be in contact with a doped fabric
What are some characteristics of aluminium dopes?
Makes the fabric lightproof and prevents damage from UV radiation
What are thinners used for?
Used to allow thinning for spraying purposes
What is MEK used for?
Used as a cleaning agent to remove wax and dirt for preparing surfaces or redoping
What does MEK stand for?
Methylethyl-ketone
What are fungicides?
Added to the first cost of dope on natural fabrics to protect from fungus and mildew
What are tack rags?
A rag that is slightly dampened with thinners and is used to wipe surfaces after sanding in preparation for the next coat
Why must you take precaution when using dope?
It has a low flash point and its vapours are dangerous
What is one of the most common causes of ignition for doped materials?
Static electricity
How do you prevent static build up?
Ground all structures
What mixed with dope causes a spontaneous combustion?
Zinc chromate
How can you control the conditions at work when doping?
Control the temperature and humidity - doping must be left overnight in a cool environment then at room temperature. Temp must be kept between 21 and 26 degrees C
Ventilation - to remove harsh and heavy vapours
Cleanliness of equipment and removal of moisture
How can humidity be tested in a room?
Use of wet and dry bulb method
Describe the application of doping on natural fabrics
Priming coat - 1st coat applied to raw fabric
- should contain fungicide and thinned to ensure penetration
Filling coat - sanded after 1st priming coat and applied at a right angles to each other before layers dry. Aluminium coat should make it lightproof
Finishing coat - number of coats will be determined as a balance between cost and quality but should not be less than 3
Describe the application of doping to polyester fabrics
Priming coat - 1st coat applied but does not require fungicide. Make sure it penetrates every fibre
Filling coat - sanded after 1st priming coat and applied at right angles to each other before previous layer dries. Aluminium doping makes it light proof
Finishing coat - fibres tend to show more and if too many coats are put on, starts to crack
Describe the application of doping on fibre glass fabrics
Priming coat - nitrate dope NOT used and 5 thin coats are applied to prevent orange peeling and filling of fibres normally
Filling coat - sanded after 1st priming coat and applied at right angles to each other before previous layer dries. Aluminium doping makes it light proof
Finishing coat - fibres tend to show more and if too many coats are put on, starts to crack
What are the considerations needed to be made for doping?
The weight of the dope applied to the fabric is an indication that the scheme has been correctly applied
When aircraft have been recovered and doped, test samples are made at the same time
The sample should be weighed before and after doping
