Wood grain orientation in a built-up spar

cmyr wrote:
In my effort to learn/remember/practice correct building
procedures,I monitor several wood aircraft design sights. In the
emerauders group,much discussion about using a wingspar that was built
and purchased by another builder. The Emeraud spar consists of 2
laminated built ip beams,w ply intercoastals, and boxed front and rear
w/ply. The spar in question was made with vertical grain wood, and
laminated with the grain perpendicular relative to the wing chord, I
believe the spar caps and laminations should have grain approx.
parallel to the wing chord. If anyone has a definitive answer that may
even prevent an accident go yo yahoo groups,emerauders

If you are referring to the laminated caps of a box beam on top and
bottom: I have seen this discussion at various stages of heat, several
times before.
The usual conclusion is that if the tree trunk is oriented along the
axis that runs from wingtip to wing tip, it's not terribly important
whether a cross section of the box beam shows vertical grain in the caps
or horizontal. the horizontal grain orientastion is slightly prefered if
I recall. I understand that even well seasoned timber can show some
progressive straightening of curved grain in the cross section, so
having any curve the same in adjacent lamina might be an idea.

Not strictly relevant: an aluminum spar designer decided to add aluminum
strips progressively in the WEB plane near top and bottom rather than on
the top and bottom faces of the I beam he used, for the sake of
convenience, at the cost of some loss of strength in bending.
This was a light single for homebuilding from a couple folks at
Loughborough Tech Aero Dept. as I recall.

Brian W

On Jun 25, 1:22�pm, Brian Whatcott wrote:
cmyr wrote:
� � �In my effort to learn/remember/practice correct building
procedures,I monitor several wood aircraft design sights. In the
emerauders group,much discussion about using a wingspar that was built
and purchased by another builder. The Emeraud spar consists of 2
laminated built ip beams,w ply intercoastals, and boxed front and rear
w/ply. The spar in question was made with vertical grain wood, and
laminated with the grain �perpendicular relative to the wing chord, I
believe the spar caps and laminations should have grain approx.
parallel to the wing chord. If anyone has a definitive answer that may
even prevent an accident go yo yahoo groups,emerauders

If you are referring to the laminated caps of a box beam on top and
bottom: I have seen this discussion at various stages of heat, several
times before.
The usual conclusion is that if the tree trunk is oriented along the
axis that runs from wingtip to wing tip, it's not terribly important
whether a cross section of the box beam shows vertical grain in the caps
or horizontal. the horizontal grain orientastion is slightly prefered if
I recall. I understand that even well seasoned timber can show some
progressive straightening of curved grain in the cross section, so
having any curve the same in adjacent lamina might be an idea.

Not strictly relevant: an aluminum spar designer decided to add aluminum
strips progressively in the WEB plane near top and bottom rather than on
the top and bottom faces of the I beam he used, for the sake of
convenience, at the cost of some loss of strength in bending.
� This was a light single for homebuilding from a couple folks at
Loughborough Tech Aero Dept. as I recall.

Brian W

As I recall , the horizontal grain orientation is preferred because
the adhesive has access to every layer of the wood in the 2 sparcaps
when joined to the front/rear ply webs. With vertical oriented caps,
only the front/rear wood layers would carry all the loads to the ply
webs when assembled.

cmyr wrote:

As I recall , the horizontal grain orientation is preferred because
the adhesive has access to every layer of the wood in the 2 sparcaps
when joined to the front/rear ply webs. With vertical oriented caps,
only the front/rear wood layers would carry all the loads to the ply
webs when assembled.


Though this seems like a sensible choice, I thought I would look in CAM
18 (repair procedures) which is now all but 50 years old, an FAA
publication long out of print, except through the EAA. It has useful
guidance on the repair of wood spars. It makes the point that glued
scarf joints should run parallel to the general direction of the grain
(sec 18.30-2(b)(2) page 6.

If that rule were applied to the web/cap interface, it seems to advocate
a vertical grain in the cap.
Diagrams of preferred joints also seem to show grain as diagonal in caps
and solid spars..... It advocates face grain in the ply webs of box
spars running in the long direction of the spar.

Brian W