Boeing F4B-1 - Page 11

c. If a member is badly damaged it must be replaced. For the purpose of the
following instructions, fuselage members are divided into two classes, namely,
struts and longerons.
The replacement of a damaged strut should be made with an identical tube.
It may be necessary to cut the tube to remove it and likewise the new member may
have to be cut in two for installation. It is of course desirable that the replacement
member be kept intact and this will be found possible in many instances if the
adjoining fittings or members are disassembled. A very close examination of this
possibility should be made before putting a splice in a new member.
If the member cannot be installed in one piece, the splice should be made with
a sleeve in the same manner as the reinforcement described in Par. b. Typical
splices are shown in Fig. 9. Although a solid sleeve is illustrated, and is to be
preferred, a reinforcement sleeve may be used. The new strut should be cut at
approximately one-quarter of its length and the ends trimmed for clearance at
assembly, the tubes to project into their fittings at least ½ inch beyond the last
bolt. The member should be fastened at the fuselage joint fittings before drilling
the sleeve. The alig;nment of the fuselage should then be checked and the holes
for the splice bolts drilled.
An examination of the fuselage, or Fig. 10 and the table accompanying, will
reveal that the longerons are not continuous throughout their length nor is their
cross-section constant. Divisions occur at the following stations: Upper longerons
-sta. 6 and 8; lower longerons-sta. 3, 4 and 5. Three methods of replacement
are therefore possible, depending upon the location of the damage.
Method 1: Cut the damaged section near the adjacent joints and splice in a
new section. The section should be cut one-quarter of its length from each joint
if possible and two splices made as directed for struts. Although this method may
be used for any bay, it. is especially applicable to the following: Upper-sta. 3-4;
lower-sta. 7-8 and 8-9.
Method 2: Disconnect the longeron at the joint on one side of the damaged
portion and cut it on the other side. Make the cut at one-quarter of the length
of the section if possible. Replace the section cut out, making the one splice
required as directed for struts. This method is applicable to the following bays:
Upper-sta. 2-3, 4-6, 6-7, 7-8, 8-9, 9-10; lower-sta. 5-7 and 9-10. It may also be
used in upper bay sta. 3-4 by disconnecting the longeron at sta. 2 or 6 and in lower
bays sta. 7-8 and 8-9 by disconnecting the longeron at sta. 5 or 10.
Method 3: Replace the entire length of longeron. This will require dis-
connecting it at the terminal and intervening joints. This method may be used in
any longeron replacement but is especially applicable to damages in the following
lower bays: Sta. 2-3, 3-4 and 4-5.
Methods 2 and 3 will require a certain amount of disassembly of the fuselage
and an investigation of this should be made before selecting the method of replace-
ment. Temporary emergency replacements may be made with round tubing, using
a slightly larger diameter tube and squaring the ends to suit the fuselage fittings.
d. To straighten duralumin tubes, heat treat as specified above and straighten
immediately.
e. Dependable welds cannot be made on duralumin fittings and they must be
replaced when damaged. Bent duralumin fittings may be straightened without
heat treatment providing the bend does not exceed 15 ° and the bend radius is
not less than six times the thickness of the material. Heat treatment is recom-
mended in any case however.
f. Steel fittings, to which duralumin parts are attached may be welded if
great care is used. The entire fitting, except the spot to be welded, must be packed
with wet asbestos pulp to a depth of at least½ inch. The welding should be done
as rapidly as possible and a close watch kept of the condition of the finish on the
duralumin parts. If the paint starts to discolor or blister the welding must stop
as further application of heat will impair the strength of the duralumin.
Bent steel fittings may be straightened if heated in the manner described for
welding.
In connection with the repair of steel fittings, it should be remembered that
practically all these fittings have been heat-treated and any subsequent welding
or heating not followed by heat-treatment will result in a material loss of strength.
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(1' If a steel fitting cannot be welded or he~ted without da~aging attac~ed
d
0
1· · rts i·t may be found more economical to proceed with the weldmg
ura umin pa , .
and replace the damaged duralumm ~arts. . .
When replacing fittings a certam a~ount of diss~mbly o~ the fuselage will
11 be necessary. If the disassembly is found to be i!Ilpracticable, the repl_ace-
:~!t ~ay be made by cutting and splicing the connectmg members as described
above. f 11
h. The welding and repairing. of steel tubes_ can be pe_rformed success ~ Y
by ordinary welding methods provided the followmg precautions are obser~ed.
(1) No splices shall be made by butt w_el_ds ~n st_ructural me1:1be~s su~Jec_t to
direct tension or bending ~~resses, unless the 3omt is remforced by nvetmg, pinnmg,
telescoping, or other auxiliary means.
(2) Welded joints shall not be _cl_eaned up by filing, as such _treatment cause_s a
I f joint efficiency. Welded Jomts shall not be. filled wit!:: solder, braz~ng
osst
0
1 or any other fitler. The joining of parts by fillmg holes with fused weldmg
me a' . . ·tt d
wire in lieu of a nvet or bolt is not permi e .
(3) N
O
welds shall be made over a failure in an electric weld. The ca~t str1;1c-
ture of the electric weld shall first be removed by chipping off before weldmg with
the oxygen acetylene torch. .
(4) The parts to be welded shall always be cleaned with sand paper, wire
brush or sand blast.
(5) In a telescope joint the splice shall be made with a fish mouth ~orm or
diagonal cut so that the wall of the tube will not be heated at a certam cr?SS
section as in the case of butt weld .. Where practical t~e fish !Ilouth ~hape splice
shall be used in preference to the diagonal shaped splice, as it permits ~ bett
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welded bond of the tubes. The length of the cut as measured on the outside wa
of the tube shall be not less than one diameter of the tube, an~ preferably two
diameters of the tube. The ends of the prongs shall not be appreciably rounded or
flattened.
(6) The splicing shall b~ done at t~e quarter length points if practical, other-
wise as close to the strut pomt as possible.
(7) Misalignment of the tubular structure during welding due to ?ontraction
and expansion of the metal c~n be prevented by using wood braces with notches
in the ends to hold the tubes m place.
(8) Tubing used in repairs shall be equal in strength to that being rep~ired.
Particular care must be taken not to confuse the various grades of steel tubmg.
(9) Brazed or soldered parts shall ~ever be w~lded. Steel parts which have
been heat-treated to improve the physical properties of the metal shall not be
welded.
REINfORCEMENT SLEEVE
FIG. 9-FUSELAGE REPAIRS
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