Bell OH-58A Technical Manual page 56

TM 55-l52O-228-BD
AIRFRAME
(2) Honeycomb Sandwich Structures.
Refer to Figure 4-7 for the measurement
of "WL" and "D."
a sandwich panel at an angle, the
damages in the two skins may be off-set
and of different sizes.
damage on the side with the largest
damage (usually the exit side), and make
sure that the measurement includes the
damaged area on the other side. "WL" is
the largest dimension across the damage
(both sides), regardless of direction,
and must include all radiated cracks.
"D" is the distance between damages.
Take and record the measurements as
described in paragraph 4-7.a(2).
c. Fittings, Attachments, and
Splices.
(1) See paragraph 4-12.
(2) Record all damage on DA Form
2404, Figure 4-2.
d. Damage measurements apply after
cleanup and smoothing or after BDAR has
been accomplished.
tical matter, measurements must be taken
before smoothing to make a decision on
deferrability. Hence, when estimating
damage limits before cleanup and smooth-
ing, make allowance for the material
that will be removed in smoothing. This
applies particularly to cracks.
length of the crack must be included in
in the depth (CD) and length (CL)
measurements.
4-8. ALLOWABLE DAMAGE LIMITS DEFINITION.
a. The allowable damage limits
corresponding to the damage measurements
of paragraph 4-7 are designated for a
given condition as follows:
4-12
If a projectile hits
Measure the
However, as a prac-
The
CD' = Allowable depth of damage.
CL' = Allowable length (width) of
damage.
A' = Allowable area of damage.
D' = Minimum allowable distance
between damages.
WL' = Allowable largest dimension
across web/panel damage.
N = Minimum damage factor.
b. Allowable damage limits for pri-
mary structural elements are associated
with the conditions of paragraph 4-9. A
damage limit for a given condition is a
measure of the amount of damage that a
structural member can sustain and still
support the loads associated with the
given condition.
c. For a given condition, all damages
must be equal to or less than the
corresponding allowable damage limits,
and the distance between damages must be
equal to or greater than the
corresponding minimal allowable limit;
that is:
CD < CD'
CL < CL'
WL < WL'
D > D '
The aircraft may be released for flight
in that condition.
deferred, although some cleanup and
smoothing of the damage will be
required, as will inspection for damage
growth after every flight. Special con-
sideration should be given to damage
exposed to the airstream, particularly
to the effects of ram air, rain, and
petaling. Petals may vibrate in the
passing airflow, rapidly creating cracks
in the supporting base metal.
pieces of metal may peel off and damage
other parts of the aircraft. The
distance D between damage sites for most
structures has a minimum required
spacing. The spacing requirement is
expressed as a multiple factor (N) of the
measured area of damage.
Repair may be
Large