Podcast
Questions and Answers
Wood aircraft construction dates back to the early days of ______.
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 ______.
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 ______.
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 ______.
The wood species used to repair a part should be the same as that of the original whenever ______.
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When the moisture content of a wooden part is lowered, the part ______.
When the moisture content of a wooden part is lowered, the part ______.
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The shrinkage is greatest in a ______ direction, across the fibers and parallel to the growth rings.
The shrinkage is greatest in a ______ direction, across the fibers and parallel to the growth rings.
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Approval must be obtained from the airframe manufacturer or the ______ for the replacement of modified woods.
Approval must be obtained from the airframe manufacturer or the ______ for the replacement of modified woods.
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Dimensional changes can have several detrimental effects upon a ______ structure.
Dimensional changes can have several detrimental effects upon a ______ structure.
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Spruce is considered as the ______ for this table.
Spruce is considered as the ______ for this table.
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Douglas Fir may be used as a ______ for spruce in same sizes.
Douglas Fir may be used as a ______ for spruce in same sizes.
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Western Hemlock may be used as a direct ______ for spruce.
Western Hemlock may be used as a direct ______ for spruce.
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Northern White Pine properties range between ______% and 96% those of spruce.
Northern White Pine properties range between ______% and 96% those of spruce.
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White Cedar may be used as a substitute for spruce in slightly ______ sizes.
White Cedar may be used as a substitute for spruce in slightly ______ sizes.
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Poplar is slightly ______ than spruce in terms of strength properties.
Poplar is slightly ______ than spruce in terms of strength properties.
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Noble Fir is ______% deficient in shear compared to spruce.
Noble Fir is ______% deficient in shear compared to spruce.
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Hard knots in wood are acceptable if they do not exceed ______ inch in maximum diameter.
Hard knots in wood are acceptable if they do not exceed ______ inch in maximum diameter.
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Compression wood is characterized by high specific ______.
Compression wood is characterized by high specific ______.
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Spike knots run completely through the depth of a beam ______ to the annual rings.
Spike knots run completely through the depth of a beam ______ to the annual rings.
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Gluing is generally satisfactory for most types of ______.
Gluing is generally satisfactory for most types of ______.
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Material containing ______ wood is often rejected due to its detrimental effects on strength.
Material containing ______ wood is often rejected due to its detrimental effects on strength.
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Mineral streaks are acceptable as long as they do not reveal any ______.
Mineral streaks are acceptable as long as they do not reveal any ______.
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Checks are longitudinal ______ extending across the annual rings.
Checks are longitudinal ______ extending across the annual rings.
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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 _____
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 _____
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Reject wood containing obvious _____
Reject wood containing obvious _____
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Adhesives acceptable to the FAA can be identified by referring to the aircraft maintenance or repair _____
Adhesives acceptable to the FAA can be identified by referring to the aircraft maintenance or repair _____
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Adhesives must meet all of the performance requirements necessary for use in certificated civil _____
Adhesives must meet all of the performance requirements necessary for use in certificated civil _____
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Common types of adhesives used in aircraft structure fall into two general groups: casein and synthetic _____
Common types of adhesives used in aircraft structure fall into two general groups: casein and synthetic _____
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Residual alkalinity from casein adhesive may cause the new adhesive to fail to _____ properly.
Residual alkalinity from casein adhesive may cause the new adhesive to fail to _____ properly.
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Plastic resin glue has been used in wood aircraft for many _____
Plastic resin glue has been used in wood aircraft for many _____
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Resorcinol is the only known adhesive recommended and approved for use in wooden aircraft _____
Resorcinol is the only known adhesive recommended and approved for use in wooden aircraft _____
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Phenol-formaldehyde adhesive is commonly used in the manufacturing of aircraft grade _____
Phenol-formaldehyde adhesive is commonly used in the manufacturing of aircraft grade _____
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Modern adhesives should be considered first due to casein adhesive's generally considered _____ performance.
Modern adhesives should be considered first due to casein adhesive's generally considered _____ performance.
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Quality of fit and proper clamping _____ are both critical to the achievement of full joint strength.
Quality of fit and proper clamping _____ are both critical to the achievement of full joint strength.
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Epoxy adhesives are a two-part synthetic resin product and are acceptable providing they meet the requirements of paragraph _____
Epoxy adhesives are a two-part synthetic resin product and are acceptable providing they meet the requirements of paragraph _____
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Joint durability in the presence of elevated temperature or _____ is inadequate in many epoxies.
Joint durability in the presence of elevated temperature or _____ is inadequate in many epoxies.
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Thoroughly seal all wood surfaces, particularly end grain and bolt holes, with _____, epoxy, or other acceptable sealer.
Thoroughly seal all wood surfaces, particularly end grain and bolt holes, with _____, epoxy, or other acceptable sealer.
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The epoxy adhesives consist of a resin and a ______ that are mixed together.
The epoxy adhesives consist of a resin and a ______ that are mixed together.
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Pot life may vary from a few minutes to an ______.
Pot life may vary from a few minutes to an ______.
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Satisfactory bond joints in aircraft will develop full strength under all conditions of ______.
Satisfactory bond joints in aircraft will develop full strength under all conditions of ______.
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The bonding operation must obtain a continuous thin and uniform film of solid ______ in the joint.
The bonding operation must obtain a continuous thin and uniform film of solid ______ in the joint.
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Prepared surfaces should be kept covered with a clean plastic sheet to maintain ______ prior to bonding.
Prepared surfaces should be kept covered with a clean plastic sheet to maintain ______ prior to bonding.
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It is advised to clean both joint surfaces with a ______ just prior to adhesive application.
It is advised to clean both joint surfaces with a ______ just prior to adhesive application.
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Wood surfaces must be free from oil, wax, varnish, shellac, lacquer, ______, and dirt.
Wood surfaces must be free from oil, wax, varnish, shellac, lacquer, ______, and dirt.
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Roughening smooth, well-planed surfaces of normal wood before bonding is not ______.
Roughening smooth, well-planed surfaces of normal wood before bonding is not ______.
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Wetting tests help detect the presence of wax, old adhesive, and ______.
Wetting tests help detect the presence of wax, old adhesive, and ______.
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Pot life is the usable life of the adhesive from the time that it is mixed until it must be ______ onto the wood surface.
Pot life is the usable life of the adhesive from the time that it is mixed until it must be ______ onto the wood surface.
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Open assembly time is the period from when the adhesive is spread until the parts are ______ together.
Open assembly time is the period from when the adhesive is spread until the parts are ______ together.
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Closed assembly time is the period from when the structure parts are placed together until clamping ______ is applied.
Closed assembly time is the period from when the structure parts are placed together until clamping ______ is applied.
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Pressing time must be sufficient to ensure that joint ______ is adequate before handling.
Pressing time must be sufficient to ensure that joint ______ is adequate before handling.
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Do not add ______ agents to the adhesive to extend the life of the batch.
Do not add ______ agents to the adhesive to extend the life of the batch.
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After performing wetting tests, allow adequate time for wood to ______ before bonding.
After performing wetting tests, allow adequate time for wood to ______ before bonding.
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If the parts cannot be discarded, remove the partially cured ______ and clean the bond line per adhesive manufacturer’s instructions.
If the parts cannot be discarded, remove the partially cured ______ and clean the bond line per adhesive manufacturer’s instructions.
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Temperature of the bond line affects the ______ rate of the adhesive.
Temperature of the bond line affects the ______ rate of the adhesive.
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Each type of adhesive requires a specific temperature during the ______ cycle.
Each type of adhesive requires a specific temperature during the ______ cycle.
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Pressure should be applied to the joint before the adhesive becomes too thick to ______.
Pressure should be applied to the joint before the adhesive becomes too thick to ______.
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Nonuniform clamping pressure commonly results in weak and strong areas in the same ______.
Nonuniform clamping pressure commonly results in weak and strong areas in the same ______.
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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.
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.
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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.
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.
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Small brass screws may also be used advantageously when the particular parts to be bonded are relatively ______.
Small brass screws may also be used advantageously when the particular parts to be bonded are relatively ______.
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On larger members, apply pressure by means of screw clamps, such as a cabinet-maker’s bar or ______.
On larger members, apply pressure by means of screw clamps, such as a cabinet-maker’s bar or ______.
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The mechanic must examine the entire joint to assure uniform part ______ and adhesive squeeze-out.
The mechanic must examine the entire joint to assure uniform part ______ and adhesive squeeze-out.
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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.
