Questions and Answers - Aircraft Wood | Aircraft Systems

Questions and Answers - Aircraft Wood

Study Aid Questions

Fill in the Blanks

1. The ideal range of moisture content in a wood aircraft structure is ________ percent, with any readings over ________ percent providing an environment for the growth of fungus in the wood.

2. A good indication of moisture, fungal growth, and possible ________ is a ________ or ________ odor.

3. Aircraft that are exposed to large cyclic changes of ________ and ________ are especially prone to wood shrinkage that may lead to glue joint ________.

4. Glued joints are generally designed to take ________ loads.

5. Wood ________ and dry ________ are usually easy to detect. ________ may be evident as either a discoloration or a softening of the wood.

6. Dark discoloration or gray stains running along the grain are indicative of ________.

7. Inspect structural members for ________ failures, which is indicated by rupture across the wood fibers.

8. Tapping a wood structure with a light plastic hammer should produce a ________ sound.

9. ________ is the preferred choice of wood and the standard by which the other wood types are measured.

10. All solid wood and ________ should be of the highest quality and grade.

11. All woods used for structural repair of aircraft are classified as ________.

12. Pin knot clusters are acceptable if they produce only a small effect on ________.

13. ________ are acceptable if careful inspection fails to reveal any decay.

14. Checks are longitudinal ________ extending, in general across the annual rings.

15. ________ wood is characterized by high specific gravity.

16. Some of the more common adhesives that have been used in aircraft construction and repair include ________ ________ and, ________ adhesives.

17. ________ are a useful means of detecting the presence of wax on a wood surface or joint.

18. Satisfactory glue joints in aircraft should develop the ________ of the wood under all conditions of ________.

19. ________ are the most satisfactory method of fabricating an end joint between two solid members.

20. A damaged spar may be spliced at almost any point except at ________________________, or lift and interplane strut fittings.


1. A certificated mechanic who has not performed repairs to wooden aircraft before is not allowed to perform repairs to a wood aircraft structure. TRUE/FALSE

2. When inspecting an aircraft constructed or comprised of wood components the moisture content must be above 20%. TRUE/FALSE

3. Some slight sectional undulation or bulging between panels of aircraft using single plywood covering may be permissible if the wood and glue are sound. TRUE/FALSE

4. Glued joints are generally designed to take bearing loads. TRUE/FALSE

5. Dark discoloration of wood or gray stains running along the grain are indicative of water penetration. TRUE/FALSE

6. The condition of the fabric covering on plywood surfaces does not provide an useful indication of the condition of the wood underneath. TRUE/FALSE

7. Compression failures are indicated by rupture across the wood fibers. TRUE/FALSE

8. When during an inspection of a wood structure a soft and mushy area is found, the mechanic should disassemble and repair that structure. TRUE/FALSE

9. Douglas fir is the preferred choice of wood and the standard by which other woods are measured. TRUE/FALSE

10. All woods used for structural repair of aircraft are classifies as hardwoods. TRUE/FALSE

11. Wavy, curly, interlocked grain are acceptable, if local irregularities do not exceed limitations specified for spiral and diagonal grain. TRUE/FALSE

12. Hard knots are not acceptable in wood species used for aircraft repair. TRUE/FALSE

13. Checks, shakes, and splits are acceptable under certain conditions in wood repair. TRUE/FALSE

14. Decay on aircraft wooden parts for repair are never acceptable. TRUE/FALSE

15. Smooth even surfaces produced on planers and joiners with sharp knives and correct feed adjustments are the best surfaces for gluing solid wood. TRUE/FALSE

16. The proper way to prepare wood surfaces is to sand the surface with a 180 grit sandpaper. TRUE/FALSE

17. All gluing operations should be performed above 70 °F for proper performance of the adhesive. TRUE/FALSE

18. The repairs to solid or laminated spars are never permitted and the spar should be replaced with a new spar from the manufacturer or the holder of a PMA for that part. TRUE/FALSE

19. A fabric patch could be used to repair holes not exceeding 1 inch in diameter. TRUE/FALSE

20. A properly prepared and installed scarf patch is the bests repair for damaged plywood and is preferred for most skin repairs. TRUE/FALSE

Knowledge Application Questions

1. Describe what a laminated wood assembly consists of?

2. How is aircraft plywood different from laminated wood?

3. What species of wood is used as a standard for strength properties?

4. How can rot be revealed during an inspection of a wood structure?

5. What types of glues are used in aircraft wood structure repair?

6. What effects do room temperature have on gluing wood structures using resin glue or epoxy adhesives?

7. Under what condition are mineral streaks acceptable?

8. Are hard knots acceptable in aircraft quality wood?

9. Explain why compressed wood is not acceptable for aircraft wood structures?

10. Why is it necessary to examine all stains and discoloration carefully?

11. Why are light steel bushings sometimes used in wooden structures?

12. What are the results of non‐uniform gluing pressure?

13. Name three methods that are used to apply pressure to wood glue joints?

14. What is the most effective type of joint used in splicing structural members?

15. Why does the strength of a beveled scarf joint depend on the accuracy of the beveled cut?

16. Always splice and reinforce plywood webs with what type of wood?

17. What method will prevent a patch and a plywood pressure plate from adhering together due to extruding glue from the patch?

18. What areas of a wood spar may not be spliced?

19. Why are bushings made of plastic or light metal used on wooden structures?

20. What is the minimum temperature for curing wood joints with resin glue or epoxy adhesives?

Multiple Choices Questions

1. Which statement about wood decay is correct?
a. Decay that occurs before the wood is seasoned does not affect the strength of the finished piece.
b. A limited amount of certain kinds of decay is acceptable in aircraft woods since decay affects the binding between the fibers and not the fibers themselves.
c. Decay is not acceptable in any form or amount.

2. Compression failures in wood aircraft structures are characterized by buckling of the fibers that appear as streaks on the surface
a. at right angles to the growth rings.
b. parallel to the grain.
c. at right angles to the grain.

3. Glue deterioration in wood aircraft structure is indicated
a. when a joint has separated and the glue surface shows only the imprint of the wood with no wood fibers clinging to the glue.
b. when a joint has separated and the glue surface shows pieces of wood or wood fibers clinging to the glue.
c. by any joint separation.

4. When patching a plywood skin, abrupt changes in cross sectional areas which will develop dangerous stress concentration should be avoided by using
a. circular or elliptical patches.
b. square patches.
c. doublers with any desired shaped patches.

5. Laminated wood is sometimes used in the construction of highly stressed aircraft components. This wood can be identified by its
a. parallel grain construction.
b. similarity to standard plywood construction.
c. perpendicular grain construction.

6. Pin knot clusters are permitted in wood aircraft structure provided
a. they produce a small effect on grain direction.
b. they have no mineral streaks.
c. no pitch pockets are within 12”.

7. Which of the following conditions will determine acceptance of wood with mineral streaks?
a. Careful inspection fails to reveal any decay.
b. They produce only a small effect on grain direction.
c. Local irregularities do not exceed limitations specified for spiral and diagonal grain.

8. A faint line running across the grain of a wood spar generally indicates
a. compression failure.
b. shear failure.
c. decay.

9. In cases of elongated bolt holes in a wood spar or cracks in the vicinity of bolt holes,
a. it is permissible to ream the hole, plug with hardwood, and redrill.
b. the spar may be reinforced by using hardwood reinforcing plates.
c. a new section of spar should be spliced in or the spar replaced entirely.

10. Where is information found concerning acceptable species substitutions for wood materials used in aircraft repair?
a. Aircraft Specifications or Type Certificate Data Sheets.
b. Technical Standard Orders. 
c. AC 43.13‐1B.

11. The strength of a well designed and properly prepared wood splice joint is provided by the:
a. bearing surface of the wood fibers.
b. glue.
c. reinforcement plates.

12. The I beam wooden spar is routed to:
a. increase strength.
b. obtain uniform strength.
c. reduce weight.