250
14 CFR Ch. I (1–1–24 Edition)
§ 25.481
(2) The most severe combination of
loads that are likely to arise during a
lateral drift landing must be taken
into account. In absence of a more ra-
tional analysis of this condition, the
following must be investigated:
(i) A vertical load equal to 75% of the
maximum ground reaction of § 25.473
must be considered in combination
with a drag and side load of 40% and
25% respectively of that vertical load.
(ii) The shock absorber and tire de-
flections must be assumed to be 75% of
the deflection corresponding to the
maximum ground reaction of
§ 25.473(a)(2). This load case need not be
considered in combination with flat
tires.
(3) The combination of vertical and
drag components is considered to be
acting at the wheel axle centerline.
[Amdt. 25–91, 62 FR 40705, July 29, 1997; Amdt.
25–91, 62 FR 45481, Aug. 27, 1997]
§ 25.481
Tail-down landing conditions.
(a) In the tail-down attitude, the air-
plane is assumed to contact the ground
at forward velocity components, rang-
ing from V
L1
to V
L2
parallel to the
ground under the conditions prescribed
in § 25.473 with—
(1)
V
L1
equal to
V
S0
(TAS) at the ap-
propriate landing weight and in stand-
ard sea level conditions; and
(2)
V
L2
equal to
V
S0
(TAS) at the ap-
propriate landing weight and altitudes
in a hot day temperature of 41 degrees
F. above standard.
(3) The combination of vertical and
drag components considered to be act-
ing at the main wheel axle centerline.
(b) For the tail-down landing condi-
tion for airplanes with tail wheels, the
main and tail wheels are assumed to
contact the ground simultaneously, in
accordance with figure 3 of appendix A.
Ground reaction conditions on the tail
wheel are assumed to act—
(1) Vertically; and
(2) Up and aft through the axle at 45
degrees to the ground line.
(c) For the tail-down landing condi-
tion for airplanes with nose wheels, the
airplane is assumed to be at an atti-
tude corresponding to either the stall-
ing angle or the maximum angle allow-
ing clearance with the ground by each
part of the airplane other than the
main wheels, in accordance with figure
3 of appendix A, whichever is less.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–91, 62 FR 40705, July 29,
1997; Amdt. 25–94, 63 FR 8848, Feb. 23, 1998]
§ 25.483
One-gear landing conditions.
For the one-gear landing conditions,
the airplane is assumed to be in the
level attitude and to contact the
ground on one main landing gear, in
accordance with Figure 4 of Appendix
A of this part. In this attitude—
(a) The ground reactions must be the
same as those obtained on that side
under § 25.479(d)(1), and
(b) Each unbalanced external load
must be reacted by airplane inertia in
a rational or conservative manner.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–91, 62 FR 40705, July 29,
1997]
§ 25.485
Side load conditions.
In addition to § 25.479(d)(2) the fol-
lowing conditions must be considered:
(a) For the side load condition, the
airplane is assumed to be in the level
attitude with only the main wheels
contacting the ground, in accordance
with figure 5 of appendix A.
(b) Side loads of 0.8 of the vertical re-
action (on one side) acting inward and
0.6 of the vertical reaction (on the
other side) acting outward must be
combined with one-half of the max-
imum vertical ground reactions ob-
tained in the level landing conditions.
These loads are assumed to be applied
at the ground contact point and to be
resisted by the inertia of the airplane.
The drag loads may be assumed to be
zero.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–91, 62 FR 40705, July 29,
1997]
§ 25.487
Rebound landing condition.
(a) The landing gear and its sup-
porting structure must be investigated
for the loads occurring during rebound
of the airplane from the landing sur-
face.
(b) With the landing gear fully ex-
tended and not in contact with the
ground, a load factor of 20.0 must act
on the unsprung weights of the landing
gear. This load factor must act in the
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§ 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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