Wooden Structures Flashcards
What is a Truss-Type wing spar made from?
Sitka Spruce
What are spars separated by?
Compression joints
What two types of wires are in a Truss-Type wing?
Drag wires
Anti-drag wires
What do anti-drag wires do?
Oppose the force that would push the wing forward
What does a box spar do?
What loads does it take?
Stiffens wing
Takes torsional and bending loads
What are causes of failures in glued structures?
Ageing Moisture Temperature Shrinkage Fungus Oil and fuel leaks Drain hole blockage
What will weather do to deteriorate fabrics?
Allow moisture in by destroying weather proofing qualities
Where is best to carry out checks? With what removed?
Dry, well ventilated hangar with inspection panels and covers removed
What does a musty smell indicate?
Dampness, fungus
What will failure of doped fabric do to plywood skin?
Deteriorate plywood
What will moisture do?
Migrate to lowest point - rot wood
What is an issue when assessing damage?
Lack of access
What should be removed when inspecting glue lines?
How?
Protective coatings of paint
Scraping
How to probe a joint?
Use a feeler gauge
When has a glue joint failed the feeler gauge test?
If the feeler gauge penetrates the joint
What are indicators of moisture ingress and decay?
Discolouration of bushings and corrosion of screws
What does shrinkage do?
Induces stress on members, causes looseness
What to do if elongated bolt holes are visible?
Check for looseness
What can cause bruising or crushing of a structure?
Over-tightening bolts
How to detect a compression failure?
What does it cause?
Shining a light parallel to the grain
Rupture across fibres
What indicates load failure?
Joint will break away, leaving splinters
If splintering if not evident, what will be?
Glue failure
What is secondary damage?
Loads being transmitted to the other end
After cutting timber, how long is it stacked for?
60 days
How long is further drying of timber carried out for?
Approx 3 years
When are protective coverings over timber needed?
When the moisture content is the same as the surrounding atmosphere.
Moisture content should be 15% + or - 2
How is brittleness tested?
Using drop-weight or izod test
How is a splitting test carried out?
Samples split with blunt chisel to reveal grain direction
What rate growth should be rejected?
Less than 6 rings per 25mm
How long should sample testings be kept for?
No longer than 2 years
What is rift sawing?
Cutting along the radius of the rings
What is tangential sawing?
Cutting tangent to the rings
What woods are used for aircraft?
Spruce
Douglas Fir
Noble Fir
What does Dote Disease do?
How do you cut a tree with dote disease?
Occurs at the base of a living tree
Tree is cut at 10ft or more above ground
Can Blue stain timber be used on aircraft?
How does it occur?
No
Can occur after cutting due to moisture
How do you know a tree is decayed?
Burnt looking, flaky
What do Synthetic Resin Adhesives normally consist of?
Resin and hardener
How do you prep plywood surface?
Light sanding, remove dust
How do you prepare timber surface?
Roughened for keying of adhesive
What is synthetic resin pot life affected by?
Temperature
What should all joints be?
Clean and kept at room temperature
What should adhesive be when pressure is applied?
Tacky
What is the ideal curing time for adhesive?
2 days
When applying soft adhesive to hard, what does the soft do and what may it require?
Soft will absorb
May require pre-coating and drying of soft
What to avoid when assembling?
High clamping pressure
What will an increase in temperature do to the curing time?
Decrease it
What determines the cure rate?
Temperature of glue line
What should fracture faces show in testing?
At least 75% of wood fibres fractured
Why is a wet test carried out?
To test adhesive efficiency
If there are no broken fibres, what does this indicate?
Glue failure
What could cause a glue failure?
Mixing or pot life problems
What fabrics are used for fabric coating?
Unbleached linen or cotton fabric
What are cotton tapes used for?
To prevent chaffing between structure and fabric and externally where string cording is used
What two types of cords are used for stringing?
Flax and Nylon
What is covered to prevent chaffing?
Sharp edges, bolts, screws
Two covering methods
Prefabricated envelopes
Blanket method
What is Balloon (French Fell) seams?
Normally specified for fabric joints
What is a Lap Seam?
Only to be used when specified by manufacturer
What is the most commonly used seam?
Balloon (French Fell)
What is an overhand stitch used for?
When sudden changes of section occurs on trailing edges, wing tips, wing root ends
Excess material needed for turning under
3 stitches per cm, a lock stitch every 50mm
What is Beeswax used for?
Adds lubrication to assist with sewing
How to do Flaxing?
Single cord normally used unless repair scheme dictates
What is Boom Stringing?
Used on deep aerofoils, passed around rib boom instead of typical stringing
Slip stream areas
Diameter of prop plus one rib. If multi-engined, gap between slip stream is also included
What are Adhesive and Dope used for?
Used on some light aircraft on wings and tail planes to save time and give better finishing
Dope is used on wooden structures
Dope and Adhesive used on metal structures
What are draining and stitched draining eyelets put on?
Used for?
Doped or stitched on
Stitched used on marine aircraft, stops sea spray getting in
What kind of inspection panel needs replaced each time?
Woods frames
What is a Zip?
What shouldn’t you do?
V shaped
Don’t let dope get into them
How does a Spring Panel work?
Pops out
What does a Herving-Bone Stitch do?
Repairs straight tears and cuts that have good edges. Must be doped after
What is a Woods Frame?
Damage with jagged edges
When can Darning be used?
Holes smaller than 2” wide can be darned
Holes over 4” - use an insertion repair
What is a Seyboth Tester?
Only single layers are tested
Pressed down until it penetrates the fabric
What is a Maule Tester?
Spring loaded with blunt point
Pushed down on fabric - if it punctures the fabric, the fabric has failed
Most common Man-Made Fabric?
Polyester
Which two fabrics deteriorate under sunlight?
Cotton and Linen
What are the two main man-made fabrics?
Polyester and Fibreglass
Advantages of Man-Made Fabrics?
Last longer
Cheaper
Not susceptible to the type of damage natural cloths are
What is Doping used for?
Tautening
Waterproofing
Airproofing
Light proofing
Different types of dope?
Cellulose Acetate Butyrate Cellulose Nitrate (Nitrate should not be used on glass fibre)
What will dope do to paint?
Attack and soften
Use dope-proof paint
What does aluminium dope do?
Makes fabric lightproof
What do thinners do?
Allow thinning for spraying
What is MEK used for?
Cleaning
What does the first coat of dope do?
Protects against fungus and mildew
What are tack rags?
Cloths dampened with thinner, used to wipe surfaces after sanding
What is sand paper used for?
Finishing
Safety precautions of dope
Low flash point
Vapours
Static build up - ground everything
Working conditions for doping
Control temperature and humidity (temp 21-26C)
Humidity measured using wet and dry bulb method
Ventilation
Cleanness of all equipment
Coats with application to Natural Fabrics
Priming coat - should contain fungicide, thinned to ensure proper penetration
Filling coat - Sanded after priming coat, followed by aluminium dope
Finishing coat - Not normally less than 3 coats
Waxed yearly
Coats with application to Polyester
Priming coat - doesn’t require fungicide
Filling coat
Finishing coat
Coats with application to Fibreglass
Priming coat - takes about 5 thin coats to prevent peeling, nitrate dope must not be used
Filling coat
Finishing coat
