WOOD STRUCTURES Flashcards
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How would you inspect wood for rot (decay)?
Inspect for a dark discoloration of the wood surface or gray stains along the grain.
What three forms of wood are used in aircraft?
Solid, Laminated and Plywood.
What is a laminated wood assembly?
Two or more Layers glued together with the grain of all layers approximately parallel.
How is aircraft plywood constructed?
Made of an odd number of thin plies, and grains of each layer placed 90° with adjacent ply or plies.
What species of wood is used as a standard for strength?
Spruce.
Are hard knots acceptable?
Yes, within specified limits.
Why is compression wood NOT acceptable?
It is very prejudicial to strength.
When are mineral streaks acceptable?
If the inspection fails to reveal any decay.
Why is it necessary to examine all stains and discoloration?
To determine if the stains are harmless, preliminar or advanced decay.
What types of glue are used in aircraft wood structure repair?
Casein, Epoxies, Phenol-formaldehyde, resorcinol Glue.
What type of glue may have been used in OLDER AIRCRAFT construction that requires careful inspection to detect deterioration?
Casein Glue.
What types of glues are used in MODERN AIRCRAFT wood structure repair?
Resorcinol glu, Phenol-formaldehyde glue and Epoxy resin glue.
What is the minimum °F for curing wood joints with resin repair?
70°F or as specified by glue manufacturer.
Why is it important to consider the open-assembly time when gluing wooden structures?
Because 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 the air out, brings the wood surfaces together evenly and in part responsible for the strength of the glue line.
Describe the acceptable methods used to repair elongated bolt holes found in a wooden wing spar:
Remove the damaged section and splice in a new section or replace the entire spar.
Describe the characteristics of a scarf joint:
The pieces to be joint are tapered or beveled on a slope of 1 to 10 or 1 to 12.
What are the results of insufficient gluing pressure?
Thick glue and a weak joint.
What methods are used to apply pressure to wood glue joints?
Clamps, Braids, Nails, Elastic Straps, Weight, Vacuum Bags, Screws, Electric and Hydraulic power presses.
What type of joint is used in splicing structural members?
A scarf joint.
What areas of a wood spar may NOT be spliced.
Under a wing attachment, landing gear, engine mount and lift strut fittings.
What are the two primary uses for plywood skin repair?
Gusset plates and Aircraft skin.
Provide examples of at least three types of plywood skin repair:
Scarf, surface, plug, splayed and scarfed patches.
What type of patch should be used to repair small holes in thin plywood skin if the skin is less than 1/10 inch thick?
A splayed patch.
Why must the bevel cut be accurate on both pieces of wood being repaired with a scarfed joint?
The pieces must match exactly to ensure a tight glue joint.
Name at least three different types of defects found in wood:
Knots, checks, decay, splits, pitch pockets, curly grain, cross grain, dry rot.
Why should the various pieces of wood be kept in a room for at least 24 hours prior to joining?
To allow the moisture content to equalize, minimizing dimensional changes in the wood.
The maximum number of splices that should be made to any one spar?
Two.
Always splice and reinforce plywood webs with what type of wood?
The same type of plywood as the original.
Why are light steel brushing sometimes used in wooden structures?
To prevent crushing the wood when the bolts are tightened.
What is the purpose of large surface area washers when used in wooden structures?
To provide additional bearing area for hardware to help preclude damage to the wood when the hardware is tightened.
What method will prevent a patch and a plywood pressure plate from adhering together due to extruding glue form the patch?
The use of waxed paper or vinyl plastic between the patch and pressure plate.
Name several facings and core material used in bonded honeycomb structures intended for special applications:
Stainless steel, titanium, magnesium, plywood, glass, nylon and 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 consisting of open six-sided cells.
What must be done with a damaged area in a bonded honeycomb structure prior to beginning repairs?
Inspect the area, determine the damage prior removing the affected area.
A drill bit used for drilling composites should operate at approximately what speed?
20,000 rpm.
What are most common causes for delamination of a composite structure?
Sonic vibration, expansion of internal moisture, liquid leakage and manufacturing error.
What type of defect in, or damage to, a bonded honeycomb structure can be repaired using the potted repair method?
Filling the hole.
Name some of the factors that cause crazing in transparent plastic windows and windshields:
Exposure to UV, stress, improper solvents and improper handling.
How should a hole be drilled in plexiglass to avoid damage to the hole when the drill breaks through to the underside?
Backup the plastic with a piece of wood and feed the drill slowly.
What should be done to twist drills that are to be used for drilling completely through plexiglass?
Drill free of burrs, drill angle of 150°, feed the drill slowly.
