Wood

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AMT
 111
 
Aircra*
 Wood
 and
 Structural
 Repair
 
Chapter
 6
 

What
 plane
 is
 this?
 
de Havilland Mosquito

De
 Havilland
 Mosquito
 

•  de
 Havilland
 DH98
 Mosquito
 
•  Ausie
 Mosquito
 

Wood
 

Nature’s
 composite
 material
 
Light
 weight
 and
 strong
 
Can
 be
 created
 with
 simple
 tools
 
Typical
 construcIon
 methods
 are
 very
 labor
 
intensive
 
•  Older
 wooden
 aircra*
 are
 suscepIble
 to
 rot
 and
 
delaminaIng
 because
 their
 glues
 and
 finishes
 
didn’t
 measure
 up
 to
 modern
 replacements
 
•  AC
 43-­‐13-­‐1B
 is
 the
 ulImate
 reference
 
•  Sitka
 Spruce
 is
 the
 reference
 wood
 
• 
• 
• 
• 

Wood
 

ProperIes
 of
 aircra*
 structural
 wood.
 

Wood
 

•  All
 wood
 must
 be
 aircra*
 approved
 
•  Laminated
 wood
 video
 
•  Laminated
 wood
 is
 strips
 of
 wood
 glued
 together
 
Can
 be
 used
 to
 replace
 solid
 pieces
 and
 spars
 as
 long
 
as
 it
 is
 the
 same
 quality
 wood
 and
 the
 gain
 is
 parallel
 
!  Can
 be
 used
 to
 make
 curved
 pieces
 
!  Can
 be
 stronger
 than
 solid
 pieces
 
! 

•  Plywood
 is
 laminate
 sheets
 of
 wood
 
! 

Grains
 of
 adjacent
 layers
 cross
 each
 other
 at
 either
 
45°
 or
 90°
 to
 add
 strength
 

Plywood
 

Wood
 

•  Wood
 growth
 rings
 
! 

Dark
 ring
 is
 summer
 growth
 
•  Slow
 growth
 
•  Denser
 and
 heavier
 

! 

Light
 ring
 is
 spring
 growth
 
•  Fast
 growth
 

•  Wood
 shrinks
 and
 warps
 along
 the
 rings
 
•  Wood
 is
 quartersawn
 to
 create
 verIcal
 grain
 and
 
minimize
 warping
 
 

Quartersawn
 

Planks
 cut
 tangent
 to
 the
 annual
 rings
 (flat
 grain)
 distort,
 or
 warp,
 as
 their
 
 
moisture
 content
 changes.
 Planks
 cut
 across
 the
 annual
 rings
 (verIcal
 grain)
 change
 
 
their
 dimensions
 very
 li`le
 as
 moisture
 content
 changes.
 

Quartersawn
 

A
 log
 is
 quartersawn
 to
 produce
 the
 maximum
 number
 of
 planks
 with
 
 
verIcal
 “C”grain.
 Two
 methods
 of
 quartersawing
 are
 illustrated.
 

Glue
 

•  A
 glue
 joint
 is
 stronger
 than
 the
 wood
 
A
 wood
 joint
 should
 break
 at
 the
 wood
 not
 the
 glue
 
!  A
 deteriorated
 glue
 joint
 will
 break
 at
 the
 glue
 
! 

•  Show
 imprints
 of
 the
 wood
 in
 the
 glue
 
•  No
 wood
 fibers
 stuck
 to
 the
 glue
 
! 

Nails
 are
 used
 for
 clamping
 only
 and
 don’t
 add
 to
 
joint
 strength
 

•  Joint
 should
 be
 flat
 and
 straight
 
! 

Should
 have
 a
 very
 slight
 rough
 texture
 
•  The
 books
 says
 to
 use
 a
 glass
 cu`er
 
•  AC43
 say
 use
 sand
 paper
 but
 insure
 all
 saw
 dust
 is
 
removed
 

Glue
 Types
 

•  Resorcinol
 is
 the
 only
 approved
 glue
 for
 wood
 
Two-­‐part
 syntheIc
 resin
 adhesive
 consisIng
 of
 resin
 
and
 a
 hardener
 
!  Federal
 SpecificaIon
 MMM-­‐A-­‐181D
 and
 Military
 
SpecificaIon
 MIL-­‐A-­‐22397
 
! 

•  Casein
 glues
 (white
 glues
 like
 Elmers)
 should
 not
 
be
 used
 
•  PlasIc
 resin
 glue
 (urea-­‐formaldehyde
 resin
 glue)
 
should
 not
 be
 used
 
•  FAA
 says
 some
 epoxies
 are
 OK
 but
 doesn’t
 
specify
 which
 type
 

Rib
 ConstrucIon
 

•  EAA
 Video
 1
 
•  EAA
 Video
 2
 

Defects
 

Typical
 requirements
 for
 aircra*
 spruce.
 

Defects
 

Defects
 

•  Mineral
 streaks
 -­‐
 acceptable,
 providing
 careful
 
inspecIon
 fails
 to
 reveal
 any
 decay.
 
! 

Looks
 like
 discoloraIon
 le*
 by
 dried
 fluid
 

•  Decay
 is
 not
 acceptable
 in
 any
 form
 
Discolored
 –
 o*en
 black
 marks
 
!  So*
 when
 probed
 
! 

•  Damaged
 spar
 holes
 must
 be
 repaired
 
! 

Elongated
 or
 cracks
 around
 hole
 
•  Elongated
 bolt
 holes
 in
 a
 wing
 spar
 should
 not
 be
 repaired
 
by
 drilling
 the
 hole
 oversize
 and
 using
 the
 next
 larger
 size
 
bolt.
 

! 

Cut
 out
 damaged
 spar
 secIon
 and
 replace
 

Spar
 Splice
 

Defects
 

•  Cracked
 spars
 (except
 box
 spars)
 may
 be
 
repaired
 by
 bonding
 plates
 of
 spruce
 or
 plywood
 
of
 sufficient
 thickness
 to
 develop
 the
 
longitudinal
 shear
 on
 both
 sides
 of
 the
 spar
 
•  Compression
 failures
 must
 be
 repaired
 
Cracks
 
!  DeformaIon
 
!  Buckling
 at
 right
 angles
 to
 the
 grain
 
!  Looks
 like
 faint
 line
 running
 across
 the
 grain
 of
 a
 
wood
 
 
! 

Scarf
 Joint
 

Grain
 orientaIon
 for
 a
 scarfed
 glue
 joint.
 

I-­‐Beam
 

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