408
14 CFR Ch. I (1–1–14 Edition)
§ 25.391
speeds and corresponding device posi-
tions that the mechanism allows.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–72, 55 FR 29776, July 20,
1990; Amdt. 25–86, 61 FR 5222, Feb. 9, 1996]
C
ONTROL
S
URFACE AND
S
YSTEM
L
OADS
§ 25.391
Control surface loads: Gen-
eral.
The control surfaces must be de-
signed for the limit loads resulting
from the flight conditions in §§ 25.331,
25.341(a), 25.349 and 25.351 and the
ground gust conditions in § 25.415, con-
sidering the requirements for—
(a) Loads parallel to hinge line, in
§ 25.393;
(b) Pilot effort effects, in § 25.397;
(c) Trim tab effects, in § 25.407;
(d) Unsymmetrical loads, in § 25.427;
and
(e) Auxiliary aerodynamic surfaces,
in § 25.445.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–86, 61 FR 5222, Feb. 9,
1996]
§ 25.393
Loads parallel to hinge line.
(a) Control surfaces and supporting
hinge brackets must be designed for in-
ertia loads acting parallel to the hinge
line.
(b) In the absence of more rational
data, the inertia loads may be assumed
to be equal to
KW, where—
(1)
K=24 for vertical surfaces;
(2)
K=12 for horizontal surfaces; and
(3)
W=weight of the movable surfaces.
§ 25.395
Control system.
(a) Longitudinal, lateral, directional,
and drag control system and their sup-
porting structures must be designed for
loads corresponding to 125 percent of
the computed hinge moments of the
movable control surface in the condi-
tions prescribed in § 25.391.
(b) The system limit loads, except
the loads resulting from ground gusts,
need not exceed the loads that can be
produced by the pilot (or pilots) and by
automatic or power devices operating
the controls.
(c) The loads must not be less than
those resulting from application of the
minimum forces prescribed in
§ 25.397(c).
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5672, Apr. 8,
1970; Amdt. 25–72, 55 FR 29776, July 20, 1990]
§ 25.397
Control system loads.
(a)
General. The maximum and min-
imum pilot forces, specified in para-
graph (c) of this section, are assumed
to act at the appropriate control grips
or pads (in a manner simulating flight
conditions) and to be reacted at the at-
tachment of the control system to the
control surface horn.
(b)
Pilot effort effects. In the control
surface flight loading condition, the air
loads on movable surfaces and the cor-
responding deflections need not exceed
those that would result in flight from
the application of any pilot force with-
in the ranges specified in paragraph (c)
of this section. Two-thirds of the max-
imum values specified for the aileron
and elevator may be used if control
surface hinge moments are based on re-
liable data. In applying this criterion,
the effects of servo mechanisms, tabs,
and automatic pilot systems, must be
considered.
(c)
Limit pilot forces and torques. The
limit pilot forces and torques are as
follows:
Control
Maximum
forces or
torques
Minimum
forces or
torques
Aileron:
Stick ..............................
100 lbs ............
40 lbs.
Wheel
1
..........................
80 D in.-lbs
2
...
40 D in.-lbs.
Elevator:
Stick ..............................
250 lbs ............
100 lbs.
Wheel (symmetrical) .....
300 lbs ............
100 lbs.
Wheel (unsymmetrical)
3
.........................
100
lbs.
Rudder ..............................
300 lbs ............
130 lbs.
1
The critical parts of the aileron control system must be de-
signed for a single tangential force with a limit value equal to
1.25 times the couple force determined from these criteria.
2
D=wheel diameter (inches).
3
The unsymmetrical forces must be applied at one of the
normal handgrip points on the periphery of the control wheel.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–38, 41 FR 55466, Dec. 20,
1976; Amdt. 25–72, 55 FR 29776, July 20, 1990]
§ 25.399
Dual control system.
(a) Each dual control system must be
designed for the pilots operating in op-
position, using individual pilot forces
not less than—
(1) 0.75 times those obtained under
§ 25.395; or
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