MIL-PRF-24755B(SH)
4.7.7.2 Heavy weight Shock Test. When heavy weight shock testing is performed, the number of test shots and
test conditions shall be as specified by MIL-S-901.
4.7.8 Motor heat. Motor heating shall be measured as specified in the applicable motor specification. In each
test, the motor shall be installed in the fan, and a duct shall be attached to the fan discharge. Motor heat testing shall
be conducted at the fan operating point, which shall be obtained by means of a terminal throttle on the test duct.
Since neither the fan nor a suitable test stand will normally be available at the motor plant, the heat test may be
conducted at the plant of the fan manufacturer.
4.7.9 Bearing temperature. Bearing temperature shall be measured with the fan mounted in vertical with
impeller on bottom. Full load shall be obtained by means of a terminal throttle on attached test duct. Bearing outer
surface temperature shall not exceed requirements of 3.18.1(l).
4.7.10 Test schedule. The schedule for testing the fan shall be performed in the following order:
a. The following tests can be performed in any order: balance (see 4.7.4), casing tightness (see 4.7.5),
performance (see 4.7.1), aerodynamic stall (see 4.7.2), speed (see 4.7.6), motor heat (see 4.7.8), bearing temperature
(see 4.7.9), airborne noise (see 4.7.3), and vibration (see 4.7.4.1). The order of these tests shall be determined by the
manufacturer according to schedule availability. Correction of deficiencies or damages, which may have resulted
from vibration tests, shall not be performed prior to the test specified in 4.7.7.
b. High-impact shock (see 4.7.7). After conducting the high-impact shock test, tests specified in 4.7.1 and
4.7.2 shall be again conducted without correction of damages that may have occurred during the shock. Data for
tests specified in 4.7.1 and 4.7.2, one before and one after high-impact test, shall demonstrate that the fan-motor unit
satisfies performance and aerodynamic stall as follows: performance to be within ±5 percent of the volume indicated
in table II and aerodynamic stall not to occur greater than 90 percent of the fan design or rated CFM.
4.8 Composite material testing. Composite material shall be tested for flame spread, smoke obscuration,
combustion gas, ignitability, heat release, and mass consumed. Use of composite material requires NAVSEA
review of the fire and toxicity performance for the composite material system. The Nonmetallic Materials Branch of
NAVSEA has review responsibility for use of composite material systems on Naval vessels.
4.8.1 Fan casing and conduit box.
4.8.1.1 Internal fire insult. Fan casing and conduit box material shall withstand an internal fire insult as
described in the modified full-scale factory mutual test for horizontal duct FM4922 (see figure 2).
4.8.1.2 External fire insult. Fan casing and conduit box material shall withstand an external fire insult as
described on figure 3. Temperatures around the outside of the test specimen shall exceed minimum temperatures
prescribed by ASTM E119 for at least 15 minutes.
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