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|  MIL-T-18847C(AS)
3.14.4.1 Structural core. Structural core materials shall be honeycomb in
accordance with MIL-C-81986 and shall have a minimum compressive strength of
250 psi. Other structural core materials considered for use must be approved
by the Naval Air Systems Command.
3.14.4.2 Insulative core. Insulative core materials shall be in
accordance with ASD-M10357 or verified to be equivalent by certified test and
approved by the Naval Air Systems Command.
3.14.5 Filler materials. Filler materials used for structural, cosmetic,
or sealing purposes shall not crack, chip, or peel during the normal service
life of the tank.
3.14.6 Liner proof pressure. The aluminum liner shall be capable of
withstanding an internal proof pressure of 5 psig prior to adding the
composite filament wound outer structure, without deformation or leakage.
3.14.7 Liner preparation. The aluminum liner shall be satisfactorily
treated for corrosion. The liner shall also be treated to ensure an adhesive
bond between the liner and the filament wound outer structure of 600 psi
minimum lap shear strength (see 4.6.8.4.3).
3.14.8 Structural composite shell.
3.14.8.1 Filament winding. The filament winding operation shall be
performed on equipment capable of repeatable helical and circumferential
winding operations. The repeatable accuracy of the equipment between
successive passes of circumferential windings shall be 0.010 inches and
between successive passes of helical winding of 0.020 inches. Actual
winding accuracy shall be in accordance with 3.14.8.1.2. The winding pattern
shall be approved by the Naval Air Systems Command prior to construction.
Winding shall not be interrupted during a pass except for breakage (see
3.14.8.1.5).
3.14.8.1.1 Roving degradation. The guiding system for rovings shall be
such that it will not damage the rovings, such as fraying, etc, during the
winding process.
3.14.8.1.2 Roving gap. Any space between wound in place rovings, whether
in the same band or between bands, shall be not more than 0.250 inches wide.
In the regions of tooling pins the gap shall be not greater than 0.60 inches.
3.14.8.1.3 Roving bridging. There shall be no bridging of the roving over
the surface of the tank due to inverted curvature of the surface or thickness
differences between sandwich reinforcements and the primary core material or
thickness differences between adjoining sections of primary core material in
any areas of the tank that exceeds 0.500 inches in width. Length of bridge
shall not exceed 12 continuous inches and all bridging must be filled with an
appropriate filler material. In the regions of tooling pins, bridging shall
not exceed 0.600 inches.
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