Wood, Composite, and Transparent Plastic Structures (Jep & ASA)

What are the three forms of wood commonly used in aircraft construction?

-Solid
-Laminated
-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 4 different types of defects found in wood.

-Knots
-Checks
-Splits
-Pitch pockets
-Cross grain
-Shake
-curly grain
-Decay
-Dry rot
-Pin knot clusters
-Spike knots
-Compression failure

Can a section of wood containing a hard knot be used?

Yes as long as it is within specified 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 3 types of glues used in modern aircraft construction and repair?

-Resorcinol glue.
-Phenol-formaldehyde glue.
-Epoxy resin glue.

Is compression wood acceptable for structural repairs?

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, thereby minimizing dimensional change in the wood

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 wood 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.

-Clamps
-Nailing strips
-Power presses
-Brads
-Nails
-Small screws

What minimum curing tempurature should be observed when joining wood with various adhesive?

21 degrees C or 70 degrees F Unless specified by the glue manufacturer

When inspecting wood structures, why might it be important to consider stains and discolored areas?

They may be accompanied by 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 hole 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

In what areas are splices to a wood spar prohibited?

Under an attachment fitting for the wing root, landing gear, engine mount, lift or inter plane struts

What is the maximum number of splices allowed for any single spar?

2

Describe the characteristics of a scarf joint.

The pieces to be joined are tapered or beveled on a slope of 1 to 12.

Why must the beveled cuts be accurate on both pieces of wood being repaired with a scarf joint

The two pieces must match exactly to ensure a tight glue joint

What are the two primary uses for plywood in aircraft construction?

-Gusset plates
-Aircraft skin

Provide examples of at least three types of plywood skin repairs.

-Splay 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 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 extruding from the joint?

Place a piece of waxed paper or 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 it the purpose of large surface area washers when used on wooden structures?

Large washers 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
-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 the core consisting of open, six sided cells

What must be done with a damaged area in a bonded honeycomb structure prior to beginning repairs?

The area must be inspected to determine the damaged area prior to completely removing the damaged material

A drill bit used for drilling composites should operate at approximately what speed?

Use an air driven tool capable of a free speed of up to 20,000 RPM

What are the most common causes for delamination of a composite structure?

Sonic vibration
-Expansion of internal moisture
-Liquid leakage
-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 causes crazing in transparent plastic windows and windshields?

-Exposure to UV light
-Stress
-Solvents
-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 a piece of wood and feed the drill slowly

Which species of wood is considered to be the standard when comparing other woods for use in aircraft structure?

Sitka spruce

What is the basic difference between plywood and laminated wood?

The grain in each layer of laminated wood runs in the same direction. The grain in the layers of plywood runs at 90 or 45 degrees to each other

What kind of glue is recommended for making repairs to a wood aircraft structure?

Synthetic resin glue

How is aircraft plywood prepared for making a compound bend?

The wood is soaked in hot water until it is pliable

How much pressure must be applied to a glue joint in a piece of softwood to produce a strong joint?

125 to 150 PSI

What is the recommended taper for a splayed patch in a plywood aircraft wing?

A 5 to 1 taper

Why should sandpaper never be used when preparing a scarf joint in a wing spar for splicing?

The dust caused by sanding will plug the pores of the wood so the glue cannot get in to form a good bond

What is the largest hole in a plywood wing skin that can be repaired with a fabric patch?

A hole 1 inch in diameter

How long should a glue be kept under pressure when splicing a wooden aircraft wing spar?

For at least 7 hours

How is compression wood identified?

It has a high specific gravity, it appears to have an excessive growth of summer wood, and little contrast between the spring wood and the summer wood.

What is done to a splice in a wooden aircraft wing spar to strengthen the splice?

Reinforcing plates are glued to both sides of the splice

Why must abrupt changes in the cross sectional area of a wooden structural members be avoided?

Abrupt changes in the cross sectional area of a structural member concentrate stresses and can cause failure