Wood structures

Question 1

What is done to prepare a wooden aircraft for inspection?

Answer 1

1. place in a dry. well ventilated hangar
2. open all inspection covers, access panels, and removable fairings opened and
   removed
3. a moisture meter should be used to verify wood is dry if in doubt

Question 2

When using a moisture meter do determine if wood is dry - what is the ideal range?

Answer 2

8 % - 12%

Question 3

When using a moisture meter, a reading over what percent can provide an environment for fungus growth of wood?

Answer 3

20%

Question 4

When inspecting a wood aircraft what do you look for?

Answer 4

1. the wings, fuselage, and empennage should be inspected for undulation, warping,
   or any other disparity from the original shape
2. check the contours and alignment of leading and trailing edges - any distortion is
   indicative of deterioration
   a. a detailed inspection of these parts to the main wind structure is needed
   b. if deterioration is found in these components - the main wind structure may be
   affected
3. inspection of glued joints must include an inspection of the adjacent wood
   structure - glue failure and wood deterioration of often closely related
4. check wood condition for dry rot, wood decay, water penetration
5. check all metal fittings that are attached to a wood structure for looseness,
   corrosion, cracks or bending
6. inspect structural members for compression failures - indicated by rupture across
   the wood fibers

Question 5

What are 3 common factors in premature glue deterioration?

Answer 5

1. chemical reactions of the glue caused by aging or moisture, extreme temperatures,
   or a combination of these factors
2. mechanical forces caused mainly by wood shrinkage
3. development of fungal growths

Question 6

What are the steps in checking a glue line(edge of the glued joint)?

Answer 6

1. remove all protective coatings by scraping carefully
2. scrape only until the wood is revealed and glue line is clearly discernable
3. make sure the surrounding wood is dry
4. inspect the glue line using a magnifying glass
5. probe glue line with a thin feeler if no glue is detected/glue line parts - joint is
   defective if penetration is observed

Question 7

Examination of glue under a magnifying glass that does not reveal any wood fibers, but shows an imprint of the wood grain indicates what?

Answer 7

it indicates the cause of the failure was the predrying of the glue before applying pressure during manufacture of the joint

Question 8

Examination of glue under a magnifying glass that exhibits an irregular appearance with star shaped patterns indicates what?

Answer 8

it indicates that precuring of the glue occurred before pressure was applied or
that pressure had been incorrectly applied or maintained

Question 9

Dark discolorations of the wood or gray stains running along the grain indicates what?

Answer 9

water penetration

Question 10

Wood decay is evidenced by

Answer 10

1. discoloration
2. softening of the wood

Question 11

Define Dry Rot

Answer 11

permits the wood to be crushed into a dry powder

Question 12

What type screws are normally used for reinforcing glued wooden members?

Answer 12

Plain brass screws

Question 13

What type screws are normally used for reinforcing hard woods, such as mahogany or ash?

Answer 13

Steel screws

Question 14

Describe 2 ways of detecting water penetration in wooden aircraft

Answer 14

1. Remove screws from around area where water penetration is suspected -
   check degree of screw erosion and condition of surrounding area
2. Remove the bolts holding the fittings at spar root-end joints, aileron hinge
   brackets, etc - corrosion on surface of bolts and wood discoloration indicate water
   penetration

Question 15

What points on a wooden aircraft require additional attention during inspection?

Answer 15

control system openings
fastener holes
cracks or breaks in the finish
the interfaces of metal fittings and the wood structure

Question 16

What points on all aircraft require detailed inspections for water damage and corrosion?

Answer 16

windshield and window frames
area under the bottom of entrance and cargo doors
lower sections of the wing and fuselage

Question 17

Laminated wood spars may be substitutEd for solid rectangular wood spars when?

Answer 17

If the same quality wood is used in both.

Question 18

Where is infomation found concerning acceptable species substitutions for wood materials used in aircraft repair?

Answer 18

AC 43.13-1b

Question 19

A faint line running across the grain of a wood spar generally indicates

Answer 19

compression failure

Question 20

Any wooden member that has been overstressed is subject to which type of failure?

Answer 20

Compression

Question 21

When patching plywood skin, abrupt changes in cross sectional area which will develop dangerous stress concentration should be avoided by using?

Answer 21

Circular or elliptical patches

Question 22

When and how is finishing tape applied on a fabric covered aircraft?

Answer 22

Doped on after the first or second coat of dope.

Question 23

The determining factors for the selection of the correct weight of textile fabric to be used in covering any type of aircraft is the?

Answer 23

Speed of the aircraft and the maximum wing loading

Question 24

How many fabric thicknesses will be found in a French fell seam?

Answer 24

Four