Podcast
Questions and Answers
Wood aircraft construction dates back to the early days of ______ aircraft.
Wood aircraft construction dates back to the early days of ______ aircraft.
certificated
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 ______ whenever possible.
The wood species used to repair a part should be the same as that of the ______ whenever possible.
Signup and view all the answers
When the moisture content of a wooden part is lowered, the part ______.
When the moisture content of a wooden part is lowered, the part ______.
Signup and view all the answers
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.
Signup and view all the answers
Dimensional changes in wood structures can cause several detrimental effects, such as loosening of ______.
Dimensional changes in wood structures can cause several detrimental effects, such as loosening of ______.
Signup and view all the answers
Approval should be obtained from the airframe manufacturer or the ______ for the replacement of modified woods.
Approval should be obtained from the airframe manufacturer or the ______ for the replacement of modified woods.
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.
If the parts cannot be discarded, remove the partially cured ______ and clean the bond line per adhesive manufacturer’s instructions.
Signup and view all the answers
The temperature of the bond line affects the ______ rate of the adhesive.
The temperature of the bond line affects the ______ rate of the adhesive.
Signup and view all the answers
Each type of adhesive requires a specific ______ during the cure cycle.
Each type of adhesive requires a specific ______ during the cure cycle.
Signup and view all the answers
Use the recommended pressure to squeeze adhesive out into a thin, continuous ______ between the wood layers.
Use the recommended pressure to squeeze adhesive out into a thin, continuous ______ between the wood layers.
Signup and view all the answers
Nonuniform clamping ______ commonly results in weak and strong areas in the same joint.
Nonuniform clamping ______ 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 ______ to 150 pounds per square inch for softwoods.
Typical pressures when using resorcinol may vary from ______ to 150 pounds per square inch for softwoods.
Signup and view all the answers
The methods of applying ______ to joints in aircraft bonding operations range from the use of brads, nails, and clamps.
The methods of applying ______ to joints in aircraft bonding operations range from the use of brads, nails, and clamps.
Signup and view all the answers
On small joints using thin plywood for gussets, the pressure is usually applied by ______ or stapling.
On small joints using thin plywood for gussets, the pressure is usually applied by ______ or stapling.
Signup and view all the answers
The size of the nails must vary with the size of the ______.
The size of the nails must vary with the size of the ______.
Signup and view all the answers
Immediately after clamping or nailing a member, the mechanic must examine the entire joint to assure uniform part ______ and adhesive squeeze-out.
Immediately after clamping or nailing a member, the mechanic must examine the entire joint to assure uniform part ______ and adhesive squeeze-out.
Signup and view all the answers
The epoxy adhesives generally consist of a resin and a ______ that are mixed together.
The epoxy adhesives generally consist of a resin and a ______ that are mixed together.
Signup and view all the answers
Pot life may vary from a few minutes to an ______.
Pot life may vary from a few minutes to an ______.
Signup and view all the answers
Some epoxies may have unacceptable ______ characteristics not obvious in a shop test.
Some epoxies may have unacceptable ______ characteristics not obvious in a shop test.
Signup and view all the answers
Satisfactory bond joints in aircraft will develop the full strength of ______.
Satisfactory bond joints in aircraft will develop the full strength of ______.
Signup and view all the answers
The bonding operation must be carefully controlled to obtain a continuous, thin, and uniform ______ of solid adhesive.
The bonding operation must be carefully controlled to obtain a continuous, thin, and uniform ______ of solid adhesive.
Signup and view all the answers
It is recommended that no more time than necessary be permitted to elapse between final ______ and bonding.
It is recommended that no more time than necessary be permitted to elapse between final ______ and bonding.
Signup and view all the answers
The mating surfaces should be machined smooth and ______ with planers or joiners.
The mating surfaces should be machined smooth and ______ with planers or joiners.
Signup and view all the answers
Wood surfaces ready for bonding must be free from oil, wax, varnish, shellac, lacquer, ______, and other extraneous materials.
Wood surfaces ready for bonding must be free from oil, wax, varnish, shellac, lacquer, ______, and other extraneous materials.
Signup and view all the answers
Wetness tests are useful as a means of detecting the presence of ______, old adhesive, and finish.
Wetness tests are useful as a means of detecting the presence of ______, old adhesive, and finish.
Signup and view all the answers
Spread the adhesive in a thin, even layer on both surfaces to be ______.
Spread the adhesive in a thin, even layer on both surfaces to be ______.
Signup and view all the answers
Once pot life has expired, the remaining adhesive must be ______.
Once pot life has expired, the remaining adhesive must be ______.
Signup and view all the answers
Open assembly time is the period from the moment the adhesive is spread until the parts are ______ together.
Open assembly time is the period from the moment the adhesive is spread until the parts are ______ together.
Signup and view all the answers
The pressing time must be sufficient to ensure that joint ______ is adequate before handling.
The pressing time must be sufficient to ensure that joint ______ is adequate before handling.
Signup and view all the answers
Sanding should never be continued to the extent that it alters the ______ of the surface.
Sanding should never be continued to the extent that it alters the ______ of the surface.
Signup and view all the answers
If the recommended open or closed assembly periods are exceeded, the ______ process should not be continued.
If the recommended open or closed assembly periods are exceeded, the ______ process should not be continued.
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 ______.
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 ______.
Signup and view all the answers
Reject wood containing obvious ______.
Reject wood containing obvious ______.
Signup and view all the answers
Examine all stains and discoloration carefully to determine whether or not they are harmless, or in a stage of preliminary or advanced ______.
Examine all stains and discoloration carefully to determine whether or not they are harmless, or in a stage of preliminary or advanced ______.
Signup and view all the answers
To minimize shrinkage effects, use bushings that are slightly ______.
To minimize shrinkage effects, use bushings that are slightly ______.
Signup and view all the answers
Thoroughly seal all wood surfaces with ______, epoxy, or other acceptable sealer.
Thoroughly seal all wood surfaces with ______, epoxy, or other acceptable sealer.
Signup and view all the answers
The most common forms of modified woods found in aircraft construction are ______.
The most common forms of modified woods found in aircraft construction are ______.
Signup and view all the answers
Common types of adhesives include casein and synthetic ______.
Common types of adhesives include casein and synthetic ______.
Signup and view all the answers
Adhesives that are acceptable to the FAA can usually be identified in the aircraft maintenance or repair ______.
Adhesives that are acceptable to the FAA can usually be identified in the aircraft maintenance or repair ______.
Signup and view all the answers
Synthetic-resin adhesives comprise a broad family, including plastic resin glue, resorcinol, hot-pressed ______, and epoxy.
Synthetic-resin adhesives comprise a broad family, including plastic resin glue, resorcinol, hot-pressed ______, and epoxy.
Signup and view all the answers
Resorcinol is the only known adhesive recommended and approved for use in ______ aircraft structure.
Resorcinol is the only known adhesive recommended and approved for use in ______ aircraft structure.
Signup and view all the answers
Plastic resin glue (urea-formaldehyde resin glue) has been used in wood aircraft for many ______.
Plastic resin glue (urea-formaldehyde resin glue) has been used in wood aircraft for many ______.
Signup and view all the answers
Quality of fit and proper clamping pressure are both critical to the achievement of full ______ strength.
Quality of fit and proper clamping pressure are both critical to the achievement of full ______ strength.
Signup and view all the answers
Epoxy adhesives are a two-part synthetic resin product, and are acceptable providing they meet the ______ of paragraph 1-4a.
Epoxy adhesives are a two-part synthetic resin product, and are acceptable providing they meet the ______ of paragraph 1-4a.
Signup and view all the answers
Phenol-formaldehyde adhesive is commonly used in the manufacturing of aircraft grade ______.
Phenol-formaldehyde adhesive is commonly used in the manufacturing of aircraft grade ______.
Signup and view all the answers
New types of adhesives may become available in the ______.
New types of adhesives may become available in the ______.
Signup and view all the answers
Douglass Fir may be used as a substitute for _____ in same sizes.
Douglass Fir may be used as a substitute for _____ in same sizes.
Signup and view all the answers
Western Hemlock is less uniform in texture than _____.
Western Hemlock is less uniform in texture than _____.
Signup and view all the answers
Northern White Pine has properties between _____ % and 96 % those of spruce.
Northern White Pine has properties between _____ % and 96 % those of spruce.
Signup and view all the answers
White Cedar may be used as a direct substitute for spruce in _____ sizes.
White Cedar may be used as a direct substitute for spruce in _____ sizes.
Signup and view all the answers
Poplar, Yellow, is slightly less than spruce except in _____ and shear.
Poplar, Yellow, is slightly less than spruce except in _____ and shear.
Signup and view all the answers
Hard knots up to _____ inch in maximum diameter are acceptable.
Hard knots up to _____ inch in maximum diameter are acceptable.
Signup and view all the answers
Spike knots are knots running completely through the depth of a beam _____ to the annual rings.
Spike knots are knots running completely through the depth of a beam _____ to the annual rings.
Signup and view all the answers
Checks are longitudinal cracks extending across the _____ rings.
Checks are longitudinal cracks extending across the _____ rings.
Signup and view all the answers
Mineral streaks are acceptable, as long as careful inspection fails to reveal any _____ .
Mineral streaks are acceptable, as long as careful inspection fails to reveal any _____ .
Signup and view all the answers
Slightly exceeding spruce, Noble Fir is _____ % deficient in shear.
Slightly exceeding spruce, Noble Fir is _____ % deficient in shear.
Signup and view all the answers
Gluing is _____ for Noble Fir, ensuring reliability in joint structures.
Gluing is _____ for Noble Fir, ensuring reliability in joint structures.
Signup and view all the answers
_____ wood is difficult to recognize and can significantly detract from strength.
_____ wood is difficult to recognize and can significantly detract from strength.
Signup and view all the answers
Pitch pockets are acceptable in the center of a beam if they are at least _____ inches apart.
Pitch pockets are acceptable in the center of a beam if they are at least _____ inches apart.
Signup and view all the answers
Large solid pieces should be avoided due to inspection _____ .
Large solid pieces should be avoided due to inspection _____ .
Signup and view all the answers
Slightly less than spruce, the Yellow Poplar is not advisable to use as a _____ substitute.
Slightly less than spruce, the Yellow Poplar is not advisable to use as a _____ substitute.
Signup and view all the answers
Study Notes
Wood Aircraft Construction
- Wood aircraft construction dates back to the early days of certificated aircraft.
- Older airframes remain in service.
- The mechanic must carefully inspect wood structures for deterioration and continuing airworthiness.
Quality of Wood
-
Aircraft quality wood and plywood are required for repairs.
-
Selection and approval of wood for aircraft structural use requires specialized skills.
-
The same wood species should be used to repair a part whenever possible.
-
Use substitutions from Table 1-1 with approval from the airframe manufacturer or FAA.
-
Always consider shrinkage effects during repairs.
-
Shrinkage:
- Greatest in a tangential direction (across fibers and parallel to the growth rings)
- Less in a radial direction (across fibers and perpendicular to the growth rings)
- Negligible in a longitudinal direction (parallel to the fibers)
Modified Wood Products
- The most common modified wood product is plywood.
- Phenolic parts are also used in aircraft structures.
- These products are used to achieve specialized strength or durability characteristics.
Adhesives
-
Adhesives play a critical role in aircraft structures.
-
Only use adhesives that meet all performance requirements necessary for use in certificated civil aircraft.
-
Follow manufacturer's instructions for each product.
-
Acceptable Adhesives:
- Refer to the aircraft maintenance or repair manual for instructions on acceptable adhesive selection.
- Adhesives meeting Mil Specs, AMS, or TSO requirements for wooden aircraft structures are satisfactory.
- Adhesives must be compatible with existing structural materials and fabrication methods.
-
Types of Adhesives:
- Casein: Generally considered inferior to modern adhesives, deteriorates over time. Clean all traces before applying a new adhesive.
-
Synthetic-Resins:
- Plastic resin glue: May deteriorate rapidly in hot, moist environments. Consider it obsolete for repairs.
- Resorcinol: Recommended and approved for use in wooden aircraft structures. Meets strength and durability requirements.
- Phenol-formaldehyde: Cured at high temperature and pressure, not practical for structural repairs.
- Epoxy: Acceptable if they meet the requirements of paragraph 1-4a. Many epoxies have excellent properties, but may have inadequate durability in high temperature or moisture environments. Do not vary resin-to-hardener ratios.
Bonding Precautions
- Bonding operations need strict control to obtain a continuous, thin, and uniform adhesive film with adequate adhesion and penetration.
-
Important Conditions for Successful Bonding:
- Properly prepared wood surfaces.
- Good quality adhesive properly prepared and selected for the task.
- Good bonding technique consistent with manufacturer's instructions.
Preparation Of Wood Surfaces For Bonding
-
Bonding should occur shortly after final surfacing.
-
Keep prepared surfaces covered to maintain cleanliness.
-
Mating surfaces need to be machined smooth and true.
-
Planer marks, chipped or loosened grain, and other surface irregularities are not permitted.
-
Sanded Surfaces:
- Sanding softwood surfaces to be bonded is not permitted.
- When freshly machined surfaces are unavailable (ex: plywood), very light sanding with fine grit may be used to improve adhesive penetration.
-
Wetting Tests:
- Detect the presence of wax, old adhesive, or finish.
- A drop of water placed on a difficult-to-wet surface will not spread quickly.
- Good wettability only indicates potential for a satisfactory bond.
- Perform preliminary bonding tests for a definitive assessment of bonding characteristics.
Applying The Adhesive
- Spread a thin, even layer of adhesive on both surfaces to be joined.
- Use a clean brush and ensure complete coverage.
- Adhesive on only one surface is not recommended.
Assembly Time In Bonding
- Resorcinol, epoxy, and other adhesives cure through a chemical reaction.
-
Time Components:
- Pot life: Time from mixing to application. Discard expired adhesive. Do not add thinning agents.
- Open assembly time: Period from adhesive spreading until parts are clamped.
- Closed Assembly time: Period from parts being placed together until clamping pressure is applied.
- Pressing Time: Pressure applied to bond parts. Time must be sufficient for adequate joint strength before handling or machining.
Additional Notes
- Always follow the adhesive manufacturer's instructions for all time limits in the bonding process.
Bonding Process
- If the recommended open or closed assembly periods are exceeded, the bonding process should not continue.
- If feasible, discard parts.
- If parts cannot be discarded, remove the partially cured adhesive and clean the bond line per adhesive manufacturer’s instructions before applying new adhesive.
Bonding Temperature
- The temperature of the bond line affects the cure rate of the adhesive.
- Some adhesive types, for example resorcinol, require a minimum temperature that must be maintained throughout the curing process.
- Each adhesive type requires a specific temperature during the cure cycle.
- Follow the manufacturer’s recommendations.
Clamping Pressure
- Use the recommended pressure to squeeze adhesive out into a thin, continuous film between the wood layers.
- This forces air from the joint and brings the wood surfaces into intimate contact.
- Apply pressure before the adhesive becomes too thick to flow.
- Pressure is accomplished by means of clamps, presses, or other mechanical devices.
- Nonuniform clamping pressure commonly results in weak and strong areas in the same joint.
- The amount of pressure required to produce strong joints varies with the type of adhesive used and the type of wood to be bonded.
- Typical pressures when using resorcinol may vary from 125 to 150 pounds per square inch for softwoods and 150 to 200 pounds per square inch for hardwoods.
- Insufficient pressure or poorly machined wood surfaces usually result in thick bond lines indicating a weak joint.
- Some epoxy adhesives require much less clamping pressure to produce acceptable joint strength.
- Read and follow the manufacturer’s instructions in all cases.
Method of Applying Pressure
- Methods of applying pressure to joints in aircraft bonding operations range from the use of brads, nails, small screws, and clamps to the use of hydraulic and electrical power presses.
- Select appropriate clamping means to achieve sound bond joints.
Hand Nailing
- Hand nailing is used extensively in the bonding of ribs and in the application of plywood skins to the wing, control surfaces, and fuselage frames.
- Small brass screws may also be used when the particular parts to be bonded are relatively small and do not allow application of pressure by means of clamps.
- Nails and screws produce adverse after effects.
- There is a considerable risk of splitting small parts when installing nails or screws.
- Metal fasteners provide vulnerable points for moisture to enter during service.
Small Joints with Thin Plywood
- On small joints using thin plywood for gussets or where plywood is used as an outer skin, the pressure is usually applied by nailing or stapling.
- Thin plywood nailing strips are often used to spread the nailing pressure over a larger area and to facilitate removal of the nails after the adhesive has cured.
Nail Size and Placement
- The size of the nails must vary with the size of the members.
- If multiple rows of nails are required, the nails should be 1 inch apart in rows spaced 1/2 inch apart.
- The nails in adjacent rows should be staggered.
- In no case should the nails in adjacent rows be more than 3/4 inch from the nearest nail.
- The length of the nails should be such that they penetrate the wood below the joint at least 3/8 inch.
- In the case of small members, the end of the nail should not protrude through the member below the joint.
- Hit the nails with several light strokes, just seating the head into the surface of the gusset.
- Be careful not to crush the wood with a heavy hammer blow.
Nail Removal
- In some cases, the nails are removed after adhesive cure, while in others the nails are left in place.
- The nails are employed for clamping pressure during adhesive cure and must not be expected to hold members together in service.
- When deciding whether to remove nails after assembly, the mechanic should examine adjacent structure to see whether nails remain from original manufacture.
Larger Members
- On larger members (spar repairs for example), apply pressure by means of screw clamps, such as a cabinet-maker’s bar or “C-clamps.”
- Strips or blocks should be used to distribute clamping pressure and protect members from local crushing due to the limited pressure area of the clamps, especially when one member is thin (such as plywood).
- The strip or block should be at least twice as thick as the thinner member being bonded.
Post Clamping or Nailing
- Immediately after clamping or nailing a member, the mechanic must examine the entire joint to assure uniform part contact and adhesive squeeze-out.
- Wipe away excess adhesive.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Explore the essential concepts of wood aircraft construction, focusing on the importance of quality wood and inspections for airworthiness. This quiz covers the types of wood used, the effects of shrinkage, and the use of modified wood products like plywood in repairs.
