All,
Theory and reality seem to conflict, and I must correct myself.
The excerpt from my earlier email below make perfect sense with
reference only to drawing F-13147 L/R and dimensions thereon.
Unfortunately, the edge of the center section belly skin 13058-1
overlaps the belly skin of the walk box assemblies such that there is
only 2-1/4" between the edge of the center section belly skin and the
inboard edge of the inboard bead on the fuselage of 415-E Serial No.
4902. This skin is 3-5a on p. 1 of the Parts Manual, whereas the walk
box assemblies are shown on p. 43. While I am certain that a section
exists on some drawing showing how these belly skins interface and
connect, I do not presently know what drawing number it would be on.
Perhaps these three beads are more inboard than those of the Forney.
Since it is impossible to install a 4-1/2" diameter reinforcement ring
in 2-1/4" of space, it appears necessary to center the two inboard
inspection openings along the centerline of the innermost fore-aft
bead. It may be possible to relieve (slit) that portion of fore-aft
bead each reinforcement ring covers, then flattening it such that the
rivets on either side of the slit on around will result in a functional
inspection plate that is airworthy.
I find it hard to believe this problem has not yet been successfully
addressed by someone some seven years down the road from this AD!
Anybody?
Regards,
WRB
--
On Nov 29, 2009, at 00:31, William R. Bayne wrote:
After much measuring, calculating and interpolating I have come to the
conclusion that the instructions on page 8 of USB 31 in the right-hand
illustration (for aircraft with beaded bottom skin) are adequate to
the intended purpose but a dimension is needed where it says to "SEE
NOTE 2". To make sense of what follows some may want to tape a
printout of page 8 of USB-31 to the bottom of the wing for reference
(oriented with the main gear leg cutout). Keep in mind that for one
illustration to serve the purpose intended, you are looking at the
bottom of the skin on one side and the bottom of the skin on the other
side.
Draw a line running spanwise (left-right) 10" forward from the aft
edge of the belly skin (as shown for the bottom left 4" dia. opening
and for the bottom right 3" opening). Place a 4-1/2" reinforcement
ring such that said line goes horizontally through the center with the
outboard edge of said reinforcement ring inboard and almost tangent to
the innermost of the three beads in the belly skin. Trace the 3" hole
in the reinforcement ring onto the skin and that is where the lower
right inspection hole should be located. Mark the horizontal
centerline of this hole and measure the distance per the arrows with
the words "SEE NOTE 2". Project this centerline upwards to intersect
the line drawn 23" up from the bottom per the diagram such that the
two 3" inspection holes running fore-aft have a common vertical
centerline. NO ONE SHOULD CUT METAL until the preceding layout is
done and aligned (and you have verified that nothing has been
installed inside the wing that interferes with installation of the new
inspection hole or its reinforcement ring.
It would be nice to have Univair's suggestion "If you have a 3-bead
skin...you can cut the holes wherever you need to as long as they
don't impinge on the spar" incorporated in some form into a new
revision of USB-31 but, in my humble opinion, the present version of
USB 31 does allow the desired result to be achieved following Note 2
on p. 8 with triple-beaded skins locating a 3" inspection hole with a
4-1/2" reinforcement ring as described.
