Sec. 25.255 - Out-of-trim characteristics.
(a) From an initial condition with the
airplane trimmed at cruise speeds up to V
(1) A three-second movement of the longitudinal trim system at its normal rate for the particular flight condition with no aerodynamic load (or an equivalent degree of trim for airplanes that do not have a power-operated trim system), except as limited by stops in the trim system, including those required by §25.655(b) for adjustable stabilizers; or
(2) The maximum mistrim that can be sustained by the autopilot while maintaining level flight in the high speed cruising condition.
(b) In the out-of-trim condition specified in paragraph (a) of this section, when the normal acceleration is varied from +1 g to the positive and negative values specified in paragraph (c) of this section --
(1) The stick force vs. g curve must
have a positive slope at any speed up to and including V
(2) At speeds between V
(c) Except as provided in paragraphs (d) and (e) of this section, compliance with the provisions of paragraph (a) of this section must be demonstrated in flight over the acceleration range --
(1) −1 g to +2.5 g; or
(2) 0 g to 2.0 g, and extrapolating by an acceptable method to −1 g and +2.5 g.
(d) If the procedure set forth in paragraph (c)(2) of this section is used to demonstrate compliance and marginal conditions exist during flight test with regard to reversal of primary longitudinal control force, flight tests must be accomplished from the normal acceleration at which a marginal condition is found to exist to the applicable limit specified in paragraph (b)(1) of this section.
(e) During flight tests required by
paragraph (a) of this section, the limit maneuvering load factors
prescribed in §§25.333(b) and 25.337, and the maneuvering load factors
associated with probable inadvertent excursions beyond the boundaries of
the buffet onset envelopes determined under §25.251(e), need not be
exceeded. In addition, the entry speeds for flight test demonstrations at
normal acceleration values less than 1 g must be limited to the extent
necessary to accomplish a recovery without exceeding V
(f) In the out-of-trim condition
specified in paragraph (a) of this section, it must be possible from an
overspeed condition at V
(1) The maximum control forces expected in service as specified in §§25.301 and 25.397.
(2) The control force required to produce 1.5 g.
(3) The control force corresponding to buffeting or other phenomena of such intensity that it is a strong deterrent to further application of primary longitudinal control force.
[Amdt. No. 25-42, 43 FR 2322, Jan. 16, 1978]