spaschal on DSK3GDR082PROD with CFR

Federal Aviation Administration, DOT

Section 27.969

could cause leakage, must be subjected
to the following test or its equivalent:
(1) Each complete tank assembly and
its support must be vibration tested
while mounted to simulate the actual
installation.
(2) The tank assembly must be vibrated for 25 hours while two-thirds
full of any suitable fluid. The amplitude of vibration may not be less than
one thirty-second of an inch, unless
otherwise substantiated.
(3) The test frequency of vibration
must be as follows:
(i) If no frequency of vibration resulting from any r.p.m. within the normal
operating range of engine or rotor system speeds is critical, the test frequency of vibration, in number of cycles per minute must, unless a frequency based on a more rational calculation is used, be the number obtained by averaging the maximum and
minimum power-on engine speeds
(r.p.m.) for reciprocating engine powered rotorcraft or 2,000 c.p.m. for turbine engine powered rotorcraft.
(ii) If only one frequency of vibration
resulting from any r.p.m. within the
normal operating range of engine or
rotor system speeds is critical, that
frequency of vibration must be the test
frequency.
(iii) If more than one frequency of vibration resulting from any r.p.m. within the normal operating range of engine or rotor system speeds is critical,
the most critical of these frequencies
must be the test frequency.
(4) Under paragraphs (d)(3)(ii) and
(iii) of this section, the time of test
must be adjusted to accomplish the
same number of vibration cycles as
would be accomplished in 25 hours at
the frequency specified in paragraph
(d)(3)(i) of this section.
(5) During the test, the tank assembly must be rocked at the rate of 16 to
20 complete cycles per minute through
an angle of 15 degrees on both sides of
the horizontal (30 degrees total), about
the most critical axis, for 25 hours. If
motion about more than one axis is
likely to be critical, the tank must be

rocked about each critical axis for 121-2
hours.
(Secs. 313(a), 601, and 603, 72 Stat. 752, 775, 49
U.S.C. 1354(a), 1421, and 1423; sec. 6(c), 49
U.S.C. 1655(c))
[Amdt. 27-12, 42 FR 15045, Mar. 17, 1977]

Section 27.967

Fuel tank installation.

(a) Each fuel tank must be supported
so that tank loads are not concentrated on unsupported tank surfaces. In addition - 
(1) There must be pads, if necessary,
to prevent chafing between each tank
and its supports;
(2) The padding must be nonabsorbent or treated to prevent the absorption of fuel;
(3) If flexible tank liners are used,
they must be supported so that it is
not necessary for them to withstand
fluid loads; and
(4) Each interior surface of tank compartments must be smooth and free of
projections that could cause wear of
the liner unless - 
(i) There are means for protection of
the liner at those points; or
(ii) The construction of the liner
itself provides such protection.
(b) Any spaces adjacent to tank surfaces must be adequately ventilated to
avoid accumulation of fuel or fumes in
those spaces due to minor leakage. If
the tank is in a sealed compartment,
ventilation may be limited to drain
holes that prevent clogging and excessive pressure resulting from altitude
changes. If flexible tank liners are installed, the venting arrangement for
the spaces between the liner and its
container must maintain the proper relationship to tank vent pressures for
any expected flight condition.
(c) The location of each tank must
meet the requirements of Section 27.1185 (a)
and (c).
(d) No rotorcraft skin immediately
adjacent to a major air outlet from the
engine compartment may act as the
wall of the integral tank.
[Doc. No. 26352, 59 FR 50387, Oct. 3, 1994]

Section 27.969

Fuel tank expansion space.

Each fuel tank or each group of fuel
tanks with interconnected vent systems must have an expansion space of

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