Aircraft Wood Construction Quiz

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Questions and Answers

Wood aircraft construction dates back to the early days of ______.

certificated aircraft

With proper care, airframes from the 1930’s through the 1950’s have held up remarkably well considering the state of ______.

technology

All wood and plywood used in the repair of aircraft structures should be of aircraft ______.

quality

The wood species used to repair a part should be the same as that of the original whenever ______.

possible Signup and view all the answers

When the moisture content of a wooden part is lowered, the part ______.

shrinks Signup and view all the answers

The shrinkage is greatest in a ______ direction, across the fibers and parallel to the growth rings.

tangential Signup and view all the answers

Approval must be obtained from the airframe manufacturer or the ______ for the replacement of modified woods.

FAA Signup and view all the answers

Dimensional changes can have several detrimental effects upon a ______ structure.

wood Signup and view all the answers

Spruce is considered as the ______ for this table.

standard Signup and view all the answers

Douglas Fir may be used as a ______ for spruce in same sizes.

substitute Signup and view all the answers

Western Hemlock may be used as a direct ______ for spruce.

substitute Signup and view all the answers

Northern White Pine properties range between ______% and 96% those of spruce.

85 Signup and view all the answers

White Cedar may be used as a substitute for spruce in slightly ______ sizes.

reduced Signup and view all the answers

Poplar is slightly ______ than spruce in terms of strength properties.

less Signup and view all the answers

Noble Fir is ______% deficient in shear compared to spruce.

8 Signup and view all the answers

Hard knots in wood are acceptable if they do not exceed ______ inch in maximum diameter.

3/8 Signup and view all the answers

Compression wood is characterized by high specific ______.

gravity Signup and view all the answers

Spike knots run completely through the depth of a beam ______ to the annual rings.

perpendicular Signup and view all the answers

Gluing is generally satisfactory for most types of ______.

wood Signup and view all the answers

Material containing ______ wood is often rejected due to its detrimental effects on strength.

compression Signup and view all the answers

Mineral streaks are acceptable as long as they do not reveal any ______.

decay Signup and view all the answers

Checks are longitudinal ______ extending across the annual rings.

cracks Signup and view all the answers

Compression failures are characterized by a buckling of the fibers that appear as streaks on the surface of the piece substantially at right angles to the _____

grain Signup and view all the answers

Reject wood containing obvious _____

failures Signup and view all the answers

Adhesives acceptable to the FAA can be identified by referring to the aircraft maintenance or repair _____

manual Signup and view all the answers

Adhesives must meet all of the performance requirements necessary for use in certificated civil _____

aircraft Signup and view all the answers

Common types of adhesives used in aircraft structure fall into two general groups: casein and synthetic _____

resins Signup and view all the answers

Residual alkalinity from casein adhesive may cause the new adhesive to fail to _____ properly.

cure Signup and view all the answers

Plastic resin glue has been used in wood aircraft for many _____

years Signup and view all the answers

Resorcinol is the only known adhesive recommended and approved for use in wooden aircraft _____

structure Signup and view all the answers

Phenol-formaldehyde adhesive is commonly used in the manufacturing of aircraft grade _____

plywood Signup and view all the answers

Modern adhesives should be considered first due to casein adhesive's generally considered _____ performance.

inferior Signup and view all the answers

Quality of fit and proper clamping _____ are both critical to the achievement of full joint strength.

pressure Signup and view all the answers

Epoxy adhesives are a two-part synthetic resin product and are acceptable providing they meet the requirements of paragraph _____

1-4a Signup and view all the answers

Joint durability in the presence of elevated temperature or _____ is inadequate in many epoxies.

moisture Signup and view all the answers

Thoroughly seal all wood surfaces, particularly end grain and bolt holes, with _____, epoxy, or other acceptable sealer.

varnish Signup and view all the answers

The epoxy adhesives consist of a resin and a ______ that are mixed together.

hardener Signup and view all the answers

Pot life may vary from a few minutes to an ______.

hour Signup and view all the answers

Satisfactory bond joints in aircraft will develop full strength under all conditions of ______.

stress Signup and view all the answers

The bonding operation must obtain a continuous thin and uniform film of solid ______ in the joint.

adhesive Signup and view all the answers

Prepared surfaces should be kept covered with a clean plastic sheet to maintain ______ prior to bonding.

cleanliness Signup and view all the answers

It is advised to clean both joint surfaces with a ______ just prior to adhesive application.

vacuum cleaner Signup and view all the answers

Wood surfaces must be free from oil, wax, varnish, shellac, lacquer, ______, and dirt.

paint Signup and view all the answers

Roughening smooth, well-planed surfaces of normal wood before bonding is not ______.

recommended Signup and view all the answers

Wetting tests help detect the presence of wax, old adhesive, and ______.

finish Signup and view all the answers

Pot life is the usable life of the adhesive from the time that it is mixed until it must be ______ onto the wood surface.

spread Signup and view all the answers

Open assembly time is the period from when the adhesive is spread until the parts are ______ together.

clamped Signup and view all the answers

Closed assembly time is the period from when the structure parts are placed together until clamping ______ is applied.

pressure Signup and view all the answers

Pressing time must be sufficient to ensure that joint ______ is adequate before handling.

strength Signup and view all the answers

Do not add ______ agents to the adhesive to extend the life of the batch.

thinning Signup and view all the answers

After performing wetting tests, allow adequate time for wood to ______ before bonding.

dry Signup and view all the answers

If the parts cannot be discarded, remove the partially cured ______ and clean the bond line per adhesive manufacturer’s instructions.

adhesive Signup and view all the answers

Temperature of the bond line affects the ______ rate of the adhesive.

cure Signup and view all the answers

Each type of adhesive requires a specific temperature during the ______ cycle.

cure Signup and view all the answers

Pressure should be applied to the joint before the adhesive becomes too thick to ______.

flow Signup and view all the answers

Nonuniform clamping pressure commonly results in weak and strong areas in the same ______.

joint Signup and view all the answers

Typical pressures when using resorcinol may vary from 125 to 150 pounds per square inch for ______ and 150 to 200 pounds per square inch for hardwoods.

softwoods Signup and view all the answers

The methods of applying pressure to joints in aircraft bonding operations range from the use of brads, nails, small screws, and ______; to the use of hydraulic and electrical power presses.

clamps Signup and view all the answers

Small brass screws may also be used advantageously when the particular parts to be bonded are relatively ______.

small Signup and view all the answers

On larger members, apply pressure by means of screw clamps, such as a cabinet-maker’s bar or ______.

C-clamps Signup and view all the answers

The mechanic must examine the entire joint to assure uniform part ______ and adhesive squeeze-out.

contact Signup and view all the answers

Study Notes

Wood Aircraft Construction

Wood aircraft construction is an older method with many older aircraft still in service.
Mechanics are responsible for careful inspections for deterioration and airworthiness.

Wood Quality

Aircraft wood and plywood must be of aircraft quality per Army Navy Commerce Department Bulletin ANC-19.
Table 1-1 outlines permissible variations in characteristics and properties of aircraft wood.
Selection and approval of wood for aircraft structures requires specialized skills and knowledge.
When repairing, use the same wood species as the original if possible.
Refer to Table 1-1 for permissible substitutes.
Obtain approval from the airframe manufacturer or FAA for substitutions.

Shrinkage of Wood

When wood dries it shrinks, this results in a change of dimensions which can have detrimental effects on wooden structures.
Shrinkage is greatest in a tangential direction (across the fibers, parallel to growth rings).
Shrinkage is less in the radial direction (across the fibers, perpendicular to the growth rings).
Shrinkage is negligible in the longitudinal direction (parallel to the fibers).
To minimize shrinkage issues consider using bushings that are slightly short, feathering plywood faceplates, and sealing wood surfaces with varnish, epoxy or other acceptable sealers.

Modified Wood Products and Phenolic Parts

Plywood is the most common modified wood product used in aircraft construction.
Phenolic parts are sometimes incorporated in wood structures to provide specialized strength and durability.

Adhesives

Only use adheisves that meet the performance requirements necessary for use in certified civil aircraft.
Check the aircraft maintenance or repair manual for acceptable adhesive selection.
Adhesives meeting Military specifications (Mil Spec), Aerospace Material Specifications (AMS), or technical standard orders (TSO) are acceptable providing they are compatible with existing aircraft materials and fabrication methods.
Casein adhesives have inferior performance to modern alternatives and are prone to deterioration over time.
Casein adhesives are incompatible with many modern adhesives.
If a joint was previously bonded with casein, all traces must be scraped off before applying a new adhesive.
Synthetic-resin adhesives include plastic resin glue, resorcinol, hot-pressed Phenol, and epoxy.
Plastic resin glue (urea-formaldehyde resin glue) is no longer recommended due to susceptibility to rapid deterioration in hot, moist environments.
Resorcinol is a two-part synthetic resin adhesive recommended for use in wooden aircraft structures.
It is a two-part mixture consisting of resin and a hardener.
Quality of fit and proper clamping pressure are important for full joint strength.
Phenol-formaldehyde adhesive is commonly used in the manufacturing of aircraft grade plywood.
It is cured at elevated temperature and pressure making it unsuitable for structural repairs.
Epoxy adhesives are a two-part synthetic resin product that are acceptable if they meet the requirements of paragraph 1-4a.
Many new epoxy resin systems offer excellent working properties.
They are less critical of joint quality and clamping pressure and penetrate well into wood and plywood.
Joint durability in the presence of elevated temperature or moisture may be inadequate.
Do not vary the resin-to-hardener ratio as it affects strength, thermal, and chemical resistance.

Bonding Precautions

For satisfactory bond joints in aircraft, it is important to have a continuous thin and uniform film of solid adhesive with adequate adhesion and penetration to both surfaces of the wood.
Proper wood surface preparation is important for bonding.
The adhesive must be of good quality, properly prepared, and selected for the specific task.
Bonding technique must be consistent with the adhesive manufacturer's instructions.

Wood Surface Preparation for Bonding

It is best to bond surfaces shortly after final surfacing.
Keep prepared surfaces covered with clean plastic or other protective materials.
Surfaces should be machined smooth and true with planers, joiners, or miter saws.
Avoid planer marks, chipped or loosened grain, and other surface irregularities.
Avoid using sandpaper to smooth softwood surfaces due to the possibility of crushing fibers.
Clean both surfaces with a vacuum cleaner prior to adhesive application.
Surfaces must be free from oil, wax, varnish, shellac, lacquer, enamel, dope, sealers, paint, dust, dirt, adhesive, crayon marks, and other extraneous materials.
It is generally not recommended to roughen smooth surfaces before bonding.
When surfaces cannot be freshly machined, very light sanding with a fine grit may be used to improve adhesive penetration.
When bonding surfaces with a difficult to wet surface, wetting tests can be used to identify areas with wax, old adhesive or finish.
Water placed on a difficult to wet surface will not spread rapidly.
After wetting tests, allow adequate time for the wood to dry.
Preliminary bonding tests will ensure satisfactory bonding characteristics of the adhesive and materials for the specific use.

Applying Adhesive

Adhesive should be spread in a thin and even layer on both surfaces to be joined.
Use a clean brush to ensure all surfaces are covered.
Speading adhesive on just one surface is not recommended.
Follow the adhesive manufacturer’s application instructions.

Assembly Time in Bonding

Time is an important factor in the bonding process.
Pot life is the usable life of the adhesive from the time it is mixed until it must be spread onto the wood surface.
Open assembly time is the period from the moment the adhesive is spread until the parts are clamped together.
Closed assembly time is the period from the time the parts are laid together until clamping pressure is applied.
Pressing (or clamping) time is the duration the parts are pressed together while the adhesive cures.
It is essential to follow the manufacturer’s instructions for all time limits in the bonding process.

Bond Process Considerations

If recommended open or closed assembly periods are exceeded, do not continue the bonding process.
If feasible, discard parts, otherwise remove partially cured adhesive and clean the bond line per adhesive manufacturer's instructions.

Bonding Temperature

Bond line temperature affects adhesive cure rate.
Resorcinol adhesive requires a minimum temperature throughout the curing process.
Each adhesive type requires a specific temperature during the cure cycle.
Follow manufacturer's recommendations for temperature.

Clamping Pressure

Use recommended pressure to force air from the joint and achieve intimate contact between surfaces.
Pressure should be applied before the adhesive becomes too thick to flow, utilizing clamps, presses, or mechanical devices.
Non-uniform clamping pressure results in weak and strong areas in the joint.
Pressure required varies based on adhesive and wood type.
Resorcinol adhesive typical pressures: 125-150 psi for softwoods, 150-200 psi for hardwoods.
Insufficient pressure or poorly machined surfaces result in thick bond lines, indicating weak joints.
Some epoxy adhesives require less clamping pressure.
Always read and follow manufacturer's instructions.

Methods of Applying Pressure

Methods range from brads, nails, screws, and clamps to hydraulic and electrical power presses.
Select clamping means appropriate for achieving sound bonds.,
Hand nailing used extensively in rib bonding and plywood skin application.
Small brass screws used for small parts where clamps are impractical.
Both nails and screws have drawbacks: risk of splitting parts, vulnerable points for moisture intrusion.
Thin plywood is often nailed or stapled for gussets or outer skins.
Thin plywood nailing strips distribute pressure and facilitate nail removal after cure.
Nail size and spacing depend on member size.
Stagger nails in multiple rows.
Nail length must penetrate below the joint by at least 3/8 inches.
Avoid protruding nails through the bottom member.
Use light hammer blows to seat nail heads.
Nails may be removed after cure or left in place.
Nails provide clamping pressure but shouldn't hold members together during service.
Examine adjacent structure for original nail use before deciding to remove them.
Screw clamps, cabinet-maker's bars, or "C-clamps" used for larger members.
Use strips or blocks to distribute pressure and protect members from crushing.
Strips or blocks should be at least twice as thick as the thinner member.
After clamping or nailing, examine the joint for uniform part contact and adhesive squeeze-out.
Wipe away excess adhesive.

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Description

Test your knowledge on the principles of aircraft wood construction. This quiz covers topics from the early days of aviation to the preservation of wooden airframes. Enhance your understanding of materials and their significance in aircraft repair.