251
Federal Aviation Administration, DOT
§ 25.493
direction of motion of the unsprung
weights as they reach their limiting
positions in extending with relation to
the sprung parts of the landing gear.
§ 25.489
Ground handling conditions.
Unless otherwise prescribed, the
landing gear and airplane structure
must be investigated for the conditions
in §§ 25.491 through 25.509 with the air-
plane at the design ramp weight (the
maximum weight for ground handling
conditions). No wing lift may be con-
sidered. The shock absorbers and tires
may be assumed to be in their static
position.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5673, Apr. 8,
1970]
§ 25.491
Taxi, takeoff and landing roll.
Within the range of appropriate
ground speeds and approved weights,
the airplane structure and landing gear
are assumed to be subjected to loads
not less than those obtained when the
aircraft is operating over the roughest
ground that may reasonably be ex-
pected in normal operation.
[Amdt. 25–91, 62 FR 40705, July 29, 1997]
§ 25.493
Braked roll conditions.
(a) An airplane with a tail wheel is
assumed to be in the level attitude
with the load on the main wheels, in
accordance with figure 6 of appendix A.
The limit vertical load factor is 1.2 at
the design landing weight and 1.0 at
the design ramp weight. A drag reac-
tion equal to the vertical reaction mul-
tiplied by a coefficient of friction of
0.8, must be combined with the vertical
ground reaction and applied at the
ground contact point.
(b) For an airplane with a nose wheel
the limit vertical load factor is 1.2 at
the design landing weight, and 1.0 at
the design ramp weight. A drag reac-
tion equal to the vertical reaction,
multiplied by a coefficient of friction
of 0.8, must be combined with the
vertical reaction and applied at the
ground contact point of each wheel
with brakes. The following two atti-
tudes, in accordance with figure 6 of
appendix A, must be considered:
(1) The level attitude with the wheels
contacting the ground and the loads
distributed between the main and nose
gear. Zero pitching acceleration is as-
sumed.
(2) The level attitude with only the
main gear contacting the ground and
with the pitching moment resisted by
angular acceleration.
(c) A drag reaction lower than that
prescribed in this section may be used
if it is substantiated that an effective
drag force of 0.8 times the vertical re-
action cannot be attained under any
likely loading condition.
(d) An airplane equipped with a nose
gear must be designed to withstand the
loads arising from the dynamic pitch-
ing motion of the airplane due to sud-
den application of maximum braking
force. The airplane is considered to be
at design takeoff weight with the nose
and main gears in contact with the
ground, and with a steady-state
vertical load factor of 1.0. The steady-
state nose gear reaction must be com-
bined with the maximum incremental
nose gear vertical reaction caused by
the sudden application of maximum
braking force as described in para-
graphs (b) and (c) of this section.
(e) In the absence of a more rational
analysis, the nose gear vertical reac-
tion prescribed in paragraph (d) of this
section must be calculated according
to the following formula:
V
W
A
B
B
f AE
A
B
E
N
T
=
+
+
+ +
⎡
⎣
⎢
⎤
⎦
⎥
μ
μ
Where:
V
N
= Nose gear vertical reaction.
W
T
= Design takeoff weight.
A = Horizontal distance between the c.g. of
the airplane and the nose wheel.
B = Horizontal distance between the c.g. of
the airplane and the line joining the cen-
ters of the main wheels.
E = Vertical height of the c.g. of the airplane
above the ground in the 1.0 g static con-
dition.
μ
= Coefficient of friction of 0.80.
f = Dynamic response factor; 2.0 is to be used
unless a lower factor is substantiated. In
the absence of other information, the dy-
namic response factor f may be defined
by the equation:
f
= +
−
−
⎛
⎝
⎜⎜
⎞
⎠
⎟⎟
1
1
2
exp
πξ
ξ
Where:
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