Bell OH-58A Technical Manual page 60

TM 55-1520-228-BD
AIRFRAME
4-11. GENERAL.
a. The aircraft consists of three
main sections. The forward cabin sec-
tion extends from the cockpit nose at
FS1 to the bulkhead aft of the passenger
compartment at FS130. The aft cabin
section extends from FS130 to FS205
where the tail boom is attached. The
third section is the tail boom. Refer
to Figure 4-8.
b. The forward section utilizes alu-
minum honeycomb and sheet metal struc-
tures for the major load carrying
elements. The forward section provides
for pilot and passenger seating, fuel
cell enclosure, and pylon support.
Honeycomb sandwich is used extensively
in this section, including the upper and
lower shells, seat panels, and some
bulkhead panels.
conventional thin sheet metal construc-
Primary loads forward of FS73 are
tion.
taken by the lower console, pedestal,
and lower shell.
section between FS73 and FS130 is a X -
Z planar frame consisting of the center
post at FS73, roof beam, lower shell,
and bulkhead and enclosure at FS114 and
FS130. Refer to Figure 4-9.
c. The aft section utilizes an alumi-
num and honeycomb semimonocoque construc-
tion and provides a deck for engine
installation and a compartment under the
engine deck for electrical equipment.
This section utilizes conventional thin
sheet metal structure composed of
longerons and bulkhead frames as beam
elements and decks and skins as shear
panels. Some of the fairing and decks
are honeycomb panels.
d. The tail boom is a circular sec-
tion with a horizontal stabilizer, ver-
tical fin, and anti-torque rotor
attached. The tail boom is a full mono-
coque structure utilizing a tapered cir-
cular section of aluminum alloy skin.
Redistribution in the forward end, which
is required to transfer loads from the
4-16
The remainder is of
The cabin enclosure
monocoque structure to the four attach-
ment fittings on the fuselage, is
accomplished by the use of intercoastals
and two aluminum redistribution
bulkheads. The horizontal stabilizer
is a standard spar-rib-skin riveted
construction. The vertical fin is of
standard sandwich construction using
aluminum honeycomb core and thin
aluminum skins. The upper half of the
upper fin is composed of fiberglass skins
and honeycomb core.
e. The damage assessment procedure
described in paragraph 4-5 consists of
damage measurement, determination of the
corresponding allowable damage limit and
associated condition, and formulating
repair instructions.
recorded on DA Form 2404.
4-12. DAMAGE MEASUREMENT.
a. Refer to Figures 4-8 thru 4-15 for
location and identification of major
fuselage and tail boom structural areas.
b. Refer to paragraph 4-8 and for
each damaged element, measure the depth
"CD" and the length (width) "CL" or "WL"
of each damage.
damages and measure the "D" between
damages. Start with the worst damage.
Record these values for each damaged
element on DA 2404 and compare them with
the allowable damage limits given in
this section. Select the set of
allowable damage limits which are next
larger than the measured damage, deter-
mine the corresponding condition.
Consider whether damage could result in
flight failure of other elements.
Attempt to visualize what effect large
defections of damaged member will have
on adjacent structure.
c. Decide on whether repair can be
deferred or whether damage should be
fixed and what the condition of deferred
or repaired damage would be.
This data is
Count the number of