249
Federal Aviation Administration, DOT
§ 25.479
§ 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)(1) to ensure that the lateral
displacement of the center of gravity is
maintained within these limits.
(c)
Landing gear dimension data.
Fig-
ure 1 of appendix A contains the basic
landing gear dimension data.
[Amdt. 25–23, 35 FR 5673, Apr. 8, 1970]
§ 25.473
Landing load conditions and
assumptions.
(a) For the landing conditions speci-
fied in § 25.479 to § 25.485 the airplane is
assumed to contact the ground—
(1) In the attitudes defined in § 25.479
and § 25.481;
(2) With a limit descent velocity of 10
fps at the design landing weight (the
maximum weight for landing condi-
tions 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 condi-
tions 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 veloci-
ties.
(b) Airplane lift, not exceeding air-
plane weight, may be assumed unless
the presence of systems or procedures
significantly affects the lift.
(c) The method of analysis of air-
plane and landing gear loads must take
into account at least the following ele-
ments:
(1) Landing gear dynamic character-
istics.
(2) Spin-up and springback.
(3) Rigid body response.
(4) Structural dynamic response of
the airframe, if significant.
(d) The landing gear dynamic charac-
teristics must be validated by tests as
defined in § 25.723(a).
(e) The coefficient of friction between
the tires and the ground may be estab-
lished 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]
§ 25.477
Landing gear arrangement.
Sections 25.479 through 25.485 apply
to airplanes with conventional ar-
rangements of main and nose gears, or
main and tail gears, when normal oper-
ating techniques are used.
§ 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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