Types of defects in wood Flashcards
what are the specific requirements for wood used in aircraft construction?
The wood must have a straight grain, a limited number of knots, and minimal pitch pockets, splits, and signs of decay.
What is the maximum allowable slope of the grain for aviation-grade timber?
The maximum slope of the grain is 1:15, meaning the grain may not rise more than 1 inch (2.54 cm) in a 15-inch (38.1 cm) section of wood.
What is a knot in wood, and why can it be a defect?
A knot is a point where a branch grew from the trunk of the tree. It weakens the wood, and spike knots are not acceptable for aircraft construction or repair.
What is the purpose of using free-flowing ink on wood?
Free-flowing ink is used to help identify the direction of the grain when it is difficult to determine.
What causes compression wood, and why is it not suitable for aircraft construction?
Compression wood is caused when a tree leans during growth, causing denser, weaker wood. It is unsuitable for aircraft construction because of its reduced strength.
What are pitch pockets, and where are they acceptable in wood for aircraft construction?
Pitch pockets are small openings filled with resin within the annual rings. They are acceptable only in the center portion of a beam.
What are compression failures, and how are they identified in wood?
Compression failures occur when wood fibers buckle due to a fallen tree landing unevenly. They are identified by thread-like lines across the grain and make the wood unsuitable for use.
What is a “check” in wood, and when does it occur?
A check is a crack that runs across the annual rings, occurring during the seasoning process. Wood with checks cannot be used for aircraft.
What is a “split” in wood, and why is it a defect?
A split is a lengthwise separation caused by disrupted wood fibers, often due to poor drying. It is a defect because it weakens the wood’s structural integrity.
What is a “shake” in wood, and why is it problematic?
A shake is a crack that occurs when two annual rings separate along their boundary. It weakens the wood and makes it unusable for aircraft construction.
How can you identify wood that has been damaged by decay or fungi?
Decayed wood appears as streaks or discoloration in the grain. It will break off in chunks rather than splintering when probed with a pointed instrument.
What is dry rot, and how can it be prevented?
Dry rot is a type of brown rot caused by fungi. It can be prevented by using kiln-dried wood with a moisture content of 20% or less and applying a good surface finish.
