FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 4. Metal Structure, Welding, and Brazing | 4. Metal Repair Procedures | 4-58. Repair Methods and Precautions for Aluminum Structure
AC 43.13-1B
9/8/98
(3) To avoid concentration of load on
the end rivet and consequent tendency toward
progressive rivet failure, the splice is tapered at
the ends by tapering the backing angle and by
making it shorter than the splice bar. (See fig
ure 4-18.)
(4) The preceding principles are espe
cially important in splicing stringers on the
lower surface of stressed skin wings, where
high-tension stresses may exist. When several
adjacent stringers are spliced, stagger the
splices if possible.
k. Size of Splicing Members. When the
same material is used for the splicing members
as for the original member, the cross-section
area (i.e., the shaded areas in figure 4-17), of
the splice material will be greater than the area
of the section element which it splices. The
area of a section element (e.g., each leg of an
angle or channel) is equal to the width multi
plied by the thickness. For example, the bar
“B” in figure 4-18 is assumed to splice the up
per leg of the stringer, and the angle “A” is as
sumed to splice the bulbed leg of the stringer.
Since the splice bar “B” is not as wide as the
adjacent leg, its thickness must be increased
such that the area of bar “B” is at least equal to
the area of the upper leg of the stringer.
l. The Diameter of Rivets in Stringers.
The diameter of rivets in stringers might pref
erably be between two and three times the
thickness “t” of the leg, but must not be more
than 1/4th the width “W” of the leg. Thus,
1/8-inch rivets are chosen in the example, fig
ure 4-18. If the splices were in the lower sur
face of a wing, the end rivets would be made
the same size as the skin-attaching rivets, or
3/32 inch.
m. The Number of Rivets. The number
of rivets required on each side of the cut in a
stringer or flange may be determined from
standard text books on aircraft structures, or
may be found in tables 4-9 through 4-11.
(1) In determining the number of rivets
required in the example, figure 4-18, for at
taching the splice bar “B” to the upper leg, the
thickness “t” of the element of area being
spliced is 1/16 inch (use 0.064), the rivet size
is 1/8 inch, and table 4-9 shows that 9.9 rivets
are required per inch of width. Since the width
“W” is 1/2 inch, the actual number of rivets
required to attach the splice bar to the upper
leg on each side of the cut is 9.9 (rivets per
inch) x 0.5 (inch width) = 4.95 (use 5 rivets).
(2) For the bulbed leg of the stringer
“t” = 1/16 inch (use 0.064); AN-3 bolts are
chosen, and the number of bolts required per
inch of width = 3.3. The width “W” for this
leg, however, is 1 inch; and the actual number
of bolts required on each side of the cut is
1 x 3.3 = 3.3 (use 4 bolts). When both rivets
and bolts are used in the same splice, the bolt
holes must be accurately reamed to size. It is
preferable to use only one type of attachment,
but in the above example, the dimensions of
the legs of the bulb angle indicated rivets for
the upper leg and bolts for the bulb leg.
n. Splicing of Intermediate Frames.
The same principles used for stringer splicing
may be applied to intermediate frames when
the following point is considered. Conven
tional frames of channel or Z sections are rela
tively deep and thin compared to stringers, and
usually fail by twisting or by buckling of the
free flange. Reinforce the splice joint against
this type of failure by using a splice plate
heavier than the frame and by splicing the free
flange of the frame with a flange of the splice
plate. (See figure 4-20.) Since a frame is
likely to be subjected to bending loads, make
the length of splice plate “L” more than twice
the width “W2,” and the rivets spread out to
cover the plate.
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