Jeppesen Oral- Chapter 3 ( Wood, Composite, Transparent Structures) Flashcards
What are the three forms of wood commonly used in aircraft construction?
Solid, laminated and plywood
What type of wood 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, decay, dry rot
Can a section of wood containing a hard knot be used?
Yes within limits
What type of glue may have been used in older wooden aircraft construction that requires careful inspection to detect deterioration?
Casein glue
What are the three types of glues used in modern aircraft construction and repair?
Resorcinol glue, phenol-formaldehyde, epoxy resin
Is compression acceptable for structural repair?
`No
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 moisture content to equalize, minimizes dimensional changes to the wood
Why is it important to consider the open-assembly time when gluing wooden structures?
If maximum is exceeded, the joint may fail
Why is it important to apply the proper clamping pressure to a glue joint?
Clamping forces air out of the joint, brings the wood together evenly
Describe some of the methods used to apply pressure to glue joints
Clamps, nailing strips, power presses, brads, nail, and small screws
What minimum curing temperature should be observed when joining wood with various adhesives?
70 degrees F or recommended by manufacturer
When inspecting wood structures, why might it be important to consider stains and discolored areas?
Usually accompany decay
Describe the acceptable methods used to repair elongated bolt holes found in wooden wing spar.
Remove section containing the elognated hole and splice in a new section or replace entire spare
What type of joint is used to splice a solid or rectangular wood spar?
A scarf joint
In what areas are splices to a wood spar prohibited?
Under an attachment fitting for the wing root, landing gear, engine mount, inter-plane strut
What is the maximum number of splices allowed for any single spar?
2
Describe the characteristics of a scarf joint
Pieces are tapered or beveled on a slope of 1 to 10 or 1 to 12
Why must the beveled cut be accurate for both pieces of wood being repaired with a scarfed joint?
To ensure exact tight fit between the two
What are the two primary uses for plywood in aircraft construction?
Gusset (or reinforcing) plates and aircraft skin
Provide examples of at least three types of plywood skin repairs
Splayed patches, surface patches, plug patches, scarfed patches
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, if the hole can be cleared out to a diameter of less than 15 thickness 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 a piece of waxed paper of vinyl plastic between the patch and the pressure plate
Why are light weight 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?
Provide additional bearing area for hardware to help preclude damage to the wood when the 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
Describe the construction of a bonded honeycomb structure
Laminated structure that has a solid facing bonded to either side of a core consisting of open, six-sided cells
What must be done with a damaged area in a bonded honeycomb structure prior to beginning repairs?
Damage area must be complety removed
A drill bit used for drilling composites should have an included angle of how many degrees?
135 degrees
What are the most common causes for de-lamination of a composite structure?
Sonic vibration, expansion of internal moisture, liquid leakage
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 can cause crazing in transparent plastic window and windshields?
Exposure to UV light, solvents and improper handling
How should a hole be drilled in Plexiglas to avoid damage to the hole when the drill breaks through to the underside
Back up the plastic with piece of wood and drill slowly
