Section 25.427

14 CFR Ch. I (1-1-19 Edition)

rational analysis is used, the additional factor must not be less than 1.2.
(f) For the condition of the control
locks engaged, the control surfaces, the
control system locks, and the parts of
any control systems between the surfaces and the locks must be designed to
the resultant limit loads. Where control locks are not provided, then the
control surfaces, the control system
stops nearest the surfaces, and the
parts of any control systems between
the surfaces and the stops must be designed to the resultant limit loads. If
the control system design is such as to
allow any part of the control system to
impact with the stops due to flexibility, then the resultant impact loads
must be taken into account in deriving
the limit loads due to ground gust.
(g) For the condition of taxiing with
the control locks disengaged, or where
control locks are not provided, the following apply:
(1) The control surfaces, the control
system stops nearest the surfaces, and
the parts of any control systems between the surfaces and the stops must
be designed to the resultant limit
loads.
(2) The parts of the control systems
between the stops nearest the surfaces
and the flight deck controls must be
designed to the resultant limit loads,
except that the parts of the control
system where loads are eventually reacted by the pilot need not exceed:
(i) The loads corresponding to the
maximum pilot loads in Section 25.397(c) for
each pilot alone; or
(ii) 0.75 times these maximum loads
for each pilot when the pilot forces are
applied in the same direction.
[Amdt. 25-141, 79 FR 73468, Dec. 11, 2014]

spaschal on DSK3GDR082PROD with CFR

Section 25.427

Unsymmetrical loads.

(a) In designing the airplane for lateral gust, yaw maneuver and roll maneuver conditions, account must be
taken of unsymmetrical loads on the
empennage arising from effects such as
slipstream and aerodynamic interference with the wing, vertical fin and
other aerodynamic surfaces.
(b) The horizontal tail must be assumed to be subjected to unsymmetrical loading conditions determined as
follows:

(1) 100 percent of the maximum loading from the symmetrical maneuver
conditions of Section 25.331 and the vertical
gust conditions of Section 25.341(a) acting separately on the surface on one side of
the plane of symmetry; and
(2) 80 percent of these loadings acting
on the other side.
(c) For empennage arrangements
where the horizontal tail surfaces have
dihedral angles greater than plus or
minus 10 degrees, or are supported by
the vertical tail surfaces, the surfaces
and the supporting structure must be
designed for gust velocities specified in
Section 25.341(a) acting in any orientation at
right angles to the flight path.
(d) Unsymmetrical loading on the
empennage arising from buffet conditions of Section 25.305(e) must be taken into
account.
[Doc. No. 27902, 61 FR 5222, Feb. 9, 1996]

Section 25.445 Auxiliary
faces.

aerodynamic

(a) When significant, the aerodynamic influence between auxiliary
aerodynamic surfaces, such as outboard fins and winglets, and their supporting aerodynamic surfaces, must be
taken into account for all loading conditions including pitch, roll, and yaw
maneuvers, and gusts as specified in
Section 25.341(a) acting at any orientation at
right angles to the flight path.
(b) To provide for unsymmetrical
loading when outboard fins extend
above and below the horizontal surface,
the critical vertical surface loading
(load per unit area) determined under
Section 25.391 must also be applied as follows:
(1) 100 percent to the area of the
vertical surfaces above (or below) the
horizontal surface.
(2) 80 percent to the area below (or
above) the horizontal surface.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-86, 61 FR 5222, Feb. 9,
1996]

Section 25.457

Wing flaps.

Wing flaps, their operating mechanisms, and their supporting structures
must be designed for critical loads occurring in the conditions prescribed in
Section 25.345, accounting for the loads occurring during transition from one flap position and airspeed to another.

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