Federal Aviation Administration, DOT
Section 25.459

Section 25.479

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]

GROUND LOADS

spaschal on DSK3GDR082PROD with CFR

Section 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 condition, 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 critical centers of gravity within the range
for which certification is requested
must be selected so that the maximum
design loads are obtained in each landing gear element. Fore and aft,
vertical, and lateral airplane centers of
gravity must be considered. Lateral
displacements of the c.g. from the airplane 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 effects of these lateral c.g. displacements
on the loading of the main gear elements, 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 loading or fuel usage; and
(2) Appropriate loading instructions
for random disposable loads are included
under
the
provisions
of
Section 25.1583(c)(1) to ensure that the lateral
displacement of the center of gravity is
maintained within these limits.
(c) Landing gear dimension data. Figure 1 of appendix A contains the basic
landing gear dimension data.
[Amdt. 25-23, 35 FR 5673, Apr. 8, 1970]

Section 25.473 Landing load conditions and
assumptions.
(a) For the landing conditions specified in Section 25.479 to Section 25.485 the airplane is
assumed to contact the ground - 
(1) In the attitudes defined in Section 25.479
and Section 25.481;
(2) With a limit descent velocity of 10
fps at the design landing weight (the
maximum weight for landing conditions at maximum descent velocity);
and
(3) With a limit descent velocity of 6
fps at the design take-off weight (the
maximum weight for landing conditions at a reduced descent velocity).
(4) The prescribed descent velocities
may be modified if it is shown that the
airplane has design features that make
it impossible to develop these velocities.
(b) Airplane lift, not exceeding airplane weight, may be assumed unless
the presence of systems or procedures
significantly affects the lift.
(c) The method of analysis of airplane and landing gear loads must take
into account at least the following elements:
(1) Landing gear dynamic characteristics.
(2) Spin-up and springback.
(3) Rigid body response.
(4) Structural dynamic response of
the airframe, if significant.
(d) The landing gear dynamic characteristics must be validated by tests as
defined in Section 25.723(a).
(e) The coefficient of friction between
the tires and the ground may be established by considering the effects of
skidding velocity and tire pressure.
However, this coefficient of friction
need not be more than 0.8.
[Amdt. 25-91, 62 FR 40705, July 29, 1997; Amdt.
25-91, 62 FR 45481, Aug. 27, 1997; Amdt. 25-103,
66 FR 27394, May 16, 2001]

Section 25.477 Landing gear arrangement.
Sections 25.479 through 25.485 apply
to airplanes with conventional arrangements of main and nose gears, or
main and tail gears, when normal operating techniques are used.
Section 25.479 Level landing conditions.
(a) In the level attitude, the airplane
is assumed to contact the ground at
forward velocity components, ranging

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