Wooden Structures Flashcards
What type of wings are truss type mainly used on?
Fabric covered
Main woods used in truss type wings?
Spars- Sitka spruce
Compression members- steel or aluminium alloy
Drag and anti-drag wires- steel
What is a box spar?
A box structure built into the wing to take all of the bending and torsional loads. This also helps form the shape of the wing
What are some factors that can weaken glued structures?
Chemical damage Blocked drainage holes Mechanical damage Microbiological Oil leak or fuel contamination
What can be done to preserve woods?
Store in dry clean hangar
Keep out of strong sunlight or bad weather
What should be done before inspecting a wooden aircraft?
Externally inspected for signs of gross deformation or structure failure
What should be checked for when opening panels?
Check for a musty smell which indicated damp or fungus development
What should be done when splits are encountered?
Investigate for cause or further damage
How can the timber and glue joints inspected?
Certain “trouble spots” can be cut out for inspection or just a detailed inspection around those areas
What are access holes and how are they cut?
The cut outs for inspecting timber or glue joints.
Cut with sharp trepanning tool to prevent jagged edges
What should be done first when checking glue lines?
Carefully scrape the paint off, stopping at the wood.
How are the glue lines inspected?
Using a magnifying glass.
If defect is suspected, then probe with thin feeler gauge
What would indicate dry rot and water penetration?
Dry rot- small patches of crumbling wood
Water penetration- dark colouration and grey streaks along the grain.
What is a way to confirm water penetration in the structure?
Remove some screws and check the level of corrosion on them, which indicates what the damage is in the surrounding structure.
What should be done if water penetration is suspected on the surface?
Peel back the fabric and inspect the ply skin for damage
What are some other defects to look for on wooden aircraft?
Shrinkage Elongated bolt holes Bruising and crushing Compression failures Previous repairs
What is joint failure?
When a joint fails due to excessive mechanical loads
How long is timber stacked for before shipping?
60 days
How is timber seasoned?
Naturally in air dryer sheds for 1-3 years
Artificially (ie. kiln-dried)
Why is seasoning done?
To reduce the moisture content to almost be in equilibrium with the surrounding atmosphere.
Allows it to be pretreated.
How can the moisture levels be checked in seasoned wood test pedicels?
Moisture meter
Using an oven to see if the weight changes after heating
How is density measured?
The weight and volume are measured and compared to the level it should be based on the moisture level standard.
How is brittleness checked?
Drop weight machine
Izoid impact test
How is rate of growth measured?
Rings per inch
What is a splitting test?
The sample is split with a blunt chisel to see the direction of the grain.
How long are wood sample test records kept for?
2 years
What are the types of sawing for timber conversion?
Rift- along the radius of the rings
Tangential- tangent to annular rings
What should be done before converting timber?
End sections are marked, especially the rings direction
What are the defects that can affect converted wood?
Dote disease Decay/rot Heart shake Ring shake Compression shake Incorrect grain inclement Knots Pitch holes Blue stain
What is dotes disease?
An inherent disease found in the base of trees, burn if found after conversion.
Leaves light brown stains
How would powder adhesives be prepared?
Mixed in water following manufacturers instructions, once mixed do not dilute it.
How are liquid resins prepared?
None- they should be ready to use, unless the manufacturer info needs it diluted
How are hardeners prepared?
Follow the manufactures instructions when mixing it into the resin.
How should plywood be prepared?
Sand it down to remove fibres and surface glazing
How would timber be prepared?
Roughed with scrapper or glass paper to create a key way
What is a safe moisture range in wooden structures?
8-16
What can affect the gluing of wooden structures?
Ambient temperature
How should resin adhesives be spread upon application?
Any glue spreader
Grooved roller
Clean brush
What is the most desirable way to apply adhesive?
On both sides of join
Using grooved rubber rollers
Should completely cover the surface and be tacky when pressure is applied
What should be avoided when assembling with adhesives?
High clamping pressures
Glue coming out of the join
Trapping air between surfaces
How can uniform pressure on small parts of wood be achieved?
Screws or small pins
How does temperature affect adhesives?
Heat decreases setting time
<15C increase setting times
When should testing of wooden components be done?
As often as possible, preferably with off cut pieces from actual parts
What is a wet test for wooden components?
When the piece is submerged in water at different temperatures for different times.
What is the main loading glue lines can withstand at maximum strength?
Sheer loading
What would a wood imprint, but no fibres indicate on a glue line?
The use of surface hardened timber
Pre-cured glue before pressure was applied
How long can a resin be stored for?
Up to the date on its shelf life
What should be done when repairing casein joints?
Remove al traces of casein first
How would UF glue joints be prepared for repair?
Wipe down with a 10 weight in weight (w/w) solution of acetic acid and water and let it dry.
What is the maximum storage temperature for adhesive reins?
21C
70F
