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248 

14 CFR Ch. I (1–1–24 Edition) 

§ 25.445 

empennage arising from effects such as 
slipstream and aerodynamic inter-
ference with the wing, vertical fin and 
other aerodynamic surfaces. 

(b) The horizontal tail must be as-

sumed to be subjected to unsymmet-
rical loading conditions determined as 
follows: 

(1) 100 percent of the maximum load-

ing from the symmetrical maneuver 
conditions of § 25.331 and the vertical 
gust conditions of § 25.341(a) acting sep-
arately 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 
§ 25.341(a) acting in any orientation at 
right angles to the flight path. 

(d) Unsymmetrical loading on the 

empennage arising from buffet condi-
tions of § 25.305(e) must be taken into 
account. 

[Doc. No. 27902, 61 FR 5222, Feb. 9, 1996] 

§ 25.445

Auxiliary aerodynamic sur-

faces. 

(a) When significant, the aero-

dynamic influence between auxiliary 
aerodynamic surfaces, such as out-
board fins and winglets, and their sup-
porting aerodynamic surfaces, must be 
taken into account for all loading con-
ditions including pitch, roll, and yaw 
maneuvers, and gusts as specified in 
§ 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 
§ 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] 

§ 25.457

Wing flaps. 

Wing flaps, their operating mecha-

nisms, and their supporting structures 
must be designed for critical loads oc-
curring in the conditions prescribed in 
§ 25.345, accounting for the loads occur-
ring during transition from one flap po-
sition and airspeed to another. 

§ 25.459

Special devices. 

The loading for special devices using 

aerodynamic surfaces (such as slots, 
slats and spoilers) must be determined 
from test data. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–72, 55 FR 29776, July 20, 
1990] 

G

ROUND

L

OADS

 

§ 25.471

General. 

(a) 

Loads and equilibrium. For limit 

ground loads— 

(1) Limit ground loads obtained 

under this subpart are considered to be 
external forces applied to the airplane 
structure; and 

(2) In each specified ground load con-

dition, the external loads must be 
placed in equilibrium with the linear 
and angular inertia loads in a rational 
or conservative manner. 

(b) 

Critical centers of gravity. The crit-

ical centers of gravity within the range 
for which certification is requested 
must be selected so that the maximum 
design loads are obtained in each land-
ing gear element. Fore and aft, 
vertical, and lateral airplane centers of 
gravity must be considered. Lateral 
displacements of the c.g. from the air-
plane centerline which would result in 
main gear loads not greater than 103 
percent of the critical design load for 
symmetrical loading conditions may be 
selected without considering the ef-
fects of these lateral c.g. displacements 
on the loading of the main gear ele-
ments, or on the airplane structure 
provided— 

(1) The lateral displacement of the 

c.g. results from random passenger or 
cargo disposition within the fuselage or 
from random unsymmetrical fuel load-
ing or fuel usage; and 

(2) Appropriate loading instructions 

for random disposable loads are in-
cluded under the provisions of 
§ 25.1583(c)(2) to ensure that the lateral 

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