What are three forms of wood commonly used in aircraft construction?
Solid, laminated, and plywood
What type of would should be used when splicing or reinforcing plywood webs?
The same type of plywood as originally used
Name at least four different types of defects found in wood
Knots, checks, splits, pitch pockets, cross grain, curly grain, decay, dry rot
Can a section of wood containing a hard knot be used?
Yes, within specified limits
What type of glue may have been used in older wooden aircraft construction that requires careful inspection to detect deterioration?
What are the three types of glues used in modern aircraft construction and repair?
epoxy resin glue
Is compression wood acceptable for structural repairs?
Why should the various pieces of wood being joined be kept in the same room for at least 24 hours prior to joining?
To allow the moisture content to equalize, minimizing dimensional changes
Why is it important to consider the open-assembly time when gluing wooden structures?
If the maximum open-assembly time is exceeded the joint may fail since the glue may begin setting up before the joint is assembled
Why is it important to apply the proper clamping pressure to a glue joint?
Clamping forces air out of the joint, brings the surfaces together evenly, and is responsible for the strength of the glue line
Describe some of the methods used to apply pressure to glue joints
and small screws
What minimum curing temperature should be observed when joining wood with various adhesives?
70 degrees F or as specified by the manufacturer
When inspecting wood structures, why is it important to consider stains and discolored areas?
They usually accompany decay or rot
Describe the acceptable methods used to repair elongated bolt holes found in a wooden wing spar
Remove the section containing the elongated holes and splice in a new section, or replace the entire spar
What type of joint is used to splice a solid or rectangular wood spar?
A scarf joint
Where are splices to a wood spar prohibited?
Under an attachment fitting for the wing root,
engine mount, lift,
or inter plane strut
What is the max number of splices for a single spar?
Describe the characteristics of a scarf joint
The pieces are tapered or beveled on a slope of 1 to 10 or 1 to 12
Why must the beveled cut be accurate on both pieces of wood with a scarf joint?
They must match exactly for a tight glue joint
What are the two primary uses for plywood in aircraft construction?
Gusset (reinforcing) plates, and aircraft skin
Give three examples of plywood skin repairs
What type of patch should be used to repair small holes in thin plywood skin if the skin is less than 1/10th inch thick?
A splayed patch may be used if the hole can be cleared out to a diameter of less than 15 thicknesses of the skin
What should be done to prevent a plywood patch and the pressure plate from sticking together if glue is extruded from the joint?
Place waxed paper or vinyl plastic between the patch and the plate
Why are lightweight steel bushings sometimes used in wooden structures?
Bushings prevent the wood from being crushed when bolts are tightened
What is the purpose of large surface area washers when used on wooden structures?
Large washers provide additional bearing area for hardware to help prevent damage to wood when hardware is tightened
Name several facings and core materials used in bonded honeycomb structures intended for special applications
Stainless steel, titanium, magnesium, plywood, glass, nylon, cotton cloth
Describe the construction of a bonded honeycomb structure
It is a laminated structure that has a solid facing bonded to either side of a core made of open six sided cells.
What must be done with a damaged area in a bonded honeycomb structure before repairs?
Remove damaged area
A drill bit used for drilling composites should have an included angle of how many degrees?
What are the most common causes for delamination of a composite structure?
expansion of internal moisture,
and a manufacturing error
What type of defect in or damage to a bonded honeycomb structure can be repaired using the potted repair method?
Filling a hole
Name some of the factors that cause crazing in transparent plastic windows and windshields
How should a hole be drilled in plexiglas to avoid damage to the hole when the drill breaks through?
Back up the plastic with a piece of wood and feed the drill slowly