Wooden Structures Flashcards by Victoria Nelson

What is a Truss-Type wing spar made from?

Sitka Spruce

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What are spars separated by?

Compression joints

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What two types of wires are in a Truss-Type wing?

Drag wires

Anti-drag wires

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What do anti-drag wires do?

Oppose the force that would push the wing forward

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What does a box spar do?

What loads does it take?

Stiffens wing

Takes torsional and bending loads

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What are causes of failures in glued structures?

Ageing
Moisture 
Temperature 
Shrinkage 
Fungus 
Oil and fuel leaks 
Drain hole blockage

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What will weather do to deteriorate fabrics?

Allow moisture in by destroying weather proofing qualities

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Where is best to carry out checks? With what removed?

Dry, well ventilated hangar with inspection panels and covers removed

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What does a musty smell indicate?

Dampness, fungus

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What will failure of doped fabric do to plywood skin?

Deteriorate plywood

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What will moisture do?

Migrate to lowest point - rot wood

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What is an issue when assessing damage?

Lack of access

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What should be removed when inspecting glue lines?

How?

Protective coatings of paint

Scraping

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How to probe a joint?

Use a feeler gauge

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When has a glue joint failed the feeler gauge test?

If the feeler gauge penetrates the joint

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What are indicators of moisture ingress and decay?

Discolouration of bushings and corrosion of screws

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What does shrinkage do?

Induces stress on members, causes looseness

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What to do if elongated bolt holes are visible?

Check for looseness

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What can cause bruising or crushing of a structure?

Over-tightening bolts

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How to detect a compression failure?

What does it cause?

Shining a light parallel to the grain

Rupture across fibres

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What indicates load failure?

Joint will break away, leaving splinters

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If splintering if not evident, what will be?

Glue failure

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What is secondary damage?

Loads being transmitted to the other end

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After cutting timber, how long is it stacked for?

60 days

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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