6.3.2 Wooden Structures Flashcards
What type of structure do fabric covered aircraft have
Truss type
What may the wing spars be made from
Sika spruce and may be solid or laminated
What is the advantage of a laminated spar over a solid spar
A laminated spar is just as strong and is much cheaper
What are the wing spars on wooden aircraft separated by
Compression members made of aluminium tubing or steel
What type of loads does a built up box spar take
Torsional and bending
What conditions should an aircraft be in for inspection purposes
In a dry well ventilated hangar with all inspection panels removed
What must be done before inspecting glued joints
The aircraft must be fully dried
What is the main problem associated with inspecting glued joints
There is no good non destructive testing
Access is difficult
What shape should access holes be
Access holes should be circular in shape and special tools used to avoid jagged edges
What must be done to the edges of all access holes
They must be smoothed with fine glass paper before inspection
What must be done before checking a glue line
All protective coatings must be removed by careful scraping
How is the inspection of a glue line carried out
With a magnifying glass and feeler gauge
What must be done if penetration is had on a glue line when inspecting
The piece must be rejected
How is dry rot identified
By small patches of crumbling wood
How would water penetration be identified in wood
Dark discolouration and grey streaks
What should be done to drain holes during routine maintenance
They should be cleaned out
How is a timber shrinkage inspection carried out
By removing paint or varnish and inserting a feeler gauge
What is had when elongated bolt holes are found
Can be due to landing or shear stresses
When would bruising or crushing be found
Where someone has over tightened a bolt
What type of loads are glued joints mainly designed to take
Shear loads
What is done to timber after it has been cut
It is stacked ready for shipment for 60 days
How is timber seasoned
In drying sheds for 1-3 years
Instead of waiting 1-3 years for timber to season, is there an alternative
Kiln drying
What is the purpose of seasoning
To make sure the wood is in equilibrium with the surrounding atmosphere and it makes applying surface protection and finishes easier
What must be done when the timber has been properly seasoned
It must be tested (6 inches from the end cut off first because it may be drier than the rest)
How is the moisture content of timber determined
By weighing and drying or even better is the moisture meter
What roughly should the moisture content be
15%
How is the density of timber determined
By weighing and measuring
What testing could be carried out on timber for brittleness
izod impact testing
What rate of growth should be rejected
Less than 6 rings per 25mm
How long should test pieces be kept for
No less than 2 years
What type of sawing produces a flower face
Tangential sawing
What two types of sawing are the same
Rift and quarter
What is the worst of all defects found on timber
Dote disease
What precaution is done to help prevent the felled tree having dote disease
It is cut 10 feet from the ground as dote disease lives at the root of the living tree
How is dote disease recognised
Brownish yellow spots similar to mineral oil
What must be done to timber that is suspected to have dote disease
It should be burnt because dote disease is contagious
What is wood decay/rot
Symptoms similar to dote but occurs after the tree has been felled and promoted by large amounts of moisture
What is the limit of grade inclination for grade A and grade B spruce
1 in 15 for grade A
1 in 12 for grade B
What is heart shake
Follows a sap duct
Defect should be cut out of the timber
What is ring shake
Occurs by the parting of the annular rings caused by frost
The defect should be cut from the timber
What is the limit for knot size in timber
No larger than quarter of an inch diameter
What is blue stain
Only occurs in sapwood
Should not be used in aircraft parts
What is the advantage of using synthetic resin adhesives over mechanical methods when attaching wooden structures
Provide less stress on the joints over mechanical methods
What two parts do synthetic resin adhesives normally consist of
The resin and the hardener
In what forms can synthetic adhesives be had
Liquid and powder
What type of synthetic resin adhesives typically have longer shelf lives
Powder - not susceptible to as much deterioration
How are powder resins mixed
The powder is mixed with water before it is mixed with the hardener
It should not then be diluted
Before gluing wooden structures what must be done
Must be sanded
How many sides of the joint must be covered in adhesive
Both sides of the joint
Some adhesives contain a solvent which needs to evaporate before the joint is made - what happens if the solvent doesn’t evaporate
Bubbles are created in the joint which forms a weakness
What must be done when large surfaces are being glued together
Small vent holes should be drilled in the structure to allow trapped air to dissipate
What is the advantage to applying heat to a glued surface
The setting time of the glue will decrease
The fractured glued faces should show why when they have been tested
75% of wood fibres
What type of joints should wet tests be carried out on
One that have been conditioned for at least 2-3 weeks
In what form of stress do glued joints perform in its strongest form
Shear
