253
Federal Aviation Administration, DOT
§ 25.511
load at each wheel or to the load devel-
oped by 1.2 times the nominal max-
imum static brake torque, whichever is
less.
(b) For airplanes with nose wheels,
the pitching moment must be balanced
by rotational inertia.
(c) For airplanes with tail wheels, the
resultant of the ground reactions must
pass through the center of gravity of
the airplane.
§ 25.509
Towing loads.
(a) The towing loads specified in
paragraph (d) of this section must be
considered separately. These loads
must be applied at the towing fittings
and must act parallel to the ground. In
addition—
(1) A vertical load factor equal to 1.0
must be considered acting at the center
of gravity;
(2) The shock struts and tires must
be in their static positions; and
(3) With
W
T
as the design ramp
weight, the towing load,
F
TOW,
is—
(i) 0.3
W
T
for
W
T
less than 30,000
pounds;
(ii) (
6W
T
+ 450,000)/70 for
W
T
between
30,000 and 100,000 pounds; and
(iii) 0.15
W
T
for
W
T
over 100,000
pounds.
(b) For towing points not on the
landing gear but near the plane of sym-
metry of the airplane, the drag and
side tow load components specified for
the auxiliary gear apply. For towing
points located outboard of the main
gear, the drag and side tow load compo-
nents specified for the main gear apply.
Where the specified angle of swivel
cannot be reached, the maximum ob-
tainable angle must be used.
(c) The towing loads specified in
paragraph (d) of this section must be
reacted as follows:
(1) The side component of the towing
load at the main gear must be reacted
by a side force at the static ground line
of the wheel to which the load is ap-
plied.
(2) The towing loads at the auxiliary
gear and the drag components of the
towing loads at the main gear must be
reacted as follows:
(i) A reaction with a maximum value
equal to the vertical reaction must be
applied at the axle of the wheel to
which the load is applied. Enough air-
plane inertia to achieve equilibrium
must be applied.
(ii) The loads must be reacted by air-
plane inertia.
(d) The prescribed towing loads are as
follows:
Tow point
Position
Load
Magnitude No.
Direction
Main gear ...............................
................................................
0.75 F
TOW
per main
gear unit.
1
2
3
4
Forward, parallel to drag axis.
Forward, at 30
°
to drag axis.
Aft, parallel to drag axis.
Aft, at 30
°
to drag axis.
Auxiliary gear .........................
Swiveled forward ....................
1.0 F
TOW
...................
5
6
Forward.
Aft.
Swiveled aft ............................
......do .......................
7
8
Forward.
Aft.
Swiveled 45
°
from forward .....
0.5 F
TOW
...................
9
10
Forward, in plane of wheel.
Aft, in plane of wheel.
Swiveled 45
°
from aft .............
......do .......................
11
12
Forward, in plane of wheel.
Aft, in plane of wheel.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25–23, 35 FR 5673, Apr. 8, 1970]
§ 25.511
Ground load: unsymmetrical
loads on multiple-wheel units.
(a)
General. Multiple-wheel landing
gear units are assumed to be subjected
to the limit ground loads prescribed in
this subpart under paragraphs (b)
through (f) of this section. In addi-
tion—
(1) A tandem strut gear arrangement
is a multiple-wheel unit; and
(2) In determining the total load on a
gear unit with respect to the provisions
of paragraphs (b) through (f) of this
section, the transverse shift in the load
centroid, due to unsymmetrical load
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254
14 CFR Ch. I (1–1–24 Edition)
§ 25.519
distribution on the wheels, may be ne-
glected.
(b)
Distribution of limit loads to wheels;
tires inflated. The distribution of the
limit loads among the wheels of the
landing gear must be established for
each landing, taxiing, and ground han-
dling condition, taking into account
the effects of the following factors:
(1) The number of wheels and their
physical arrangements. For truck type
landing gear units, the effects of any
seesaw motion of the truck during the
landing impact must be considered in
determining the maximum design loads
for the fore and aft wheel pairs.
(2) Any differentials in tire diameters
resulting from a combination of manu-
facturing tolerances, tire growth, and
tire wear. A maximum tire-diameter
differential equal to
2
⁄
3
of the most un-
favorable combination of diameter
variations that is obtained when tak-
ing into account manufacturing toler-
ances, tire growth, and tire wear, may
be assumed.
(3) Any unequal tire inflation pres-
sure, assuming the maximum variation
to be
±
5 percent of the nominal tire in-
flation pressure.
(4) A runway crown of zero and a run-
way crown having a convex upward
shape that may be approximated by a
slope of 1
1
⁄
2
percent with the hori-
zontal. Runway crown effects must be
considered with the nose gear unit on
either slope of the crown.
(5) The airplane attitude.
(6) Any structural deflections.
(c)
Deflated tires. The effect of de-
flated tires on the structure must be
considered with respect to the loading
conditions specified in paragraphs (d)
through (f) of this section, taking into
account the physical arrangement of
the gear components. In addition—
(1) The deflation of any one tire for
each multiple wheel landing gear unit,
and the deflation of any two critical
tires for each landing gear unit using
four or more wheels per unit, must be
considered; and
(2) The ground reactions must be ap-
plied to the wheels with inflated tires
except that, for multiple-wheel gear
units with more than one shock strut,
a rational distribution of the ground
reactions between the deflated and in-
flated tires, accounting for the dif-
ferences in shock strut extensions re-
sulting from a deflated tire, may be
used.
(d)
Landing conditions. For one and
for two deflated tires, the applied load
to each gear unit is assumed to be 60
percent and 50 percent, respectively, of
the limit load applied to each gear for
each of the prescribed landing condi-
tions. However, for the drift landing
condition of § 25.485, 100 percent of the
vertical load must be applied.
(e)
Taxiing and ground handling condi-
tions. For one and for two deflated
tires—
(1) The applied side or drag load fac-
tor, or both factors, at the center of
gravity must be the most critical value
up to 50 percent and 40 percent, respec-
tively, of the limit side or drag load
factors, or both factors, corresponding
to the most severe condition resulting
from consideration of the prescribed
taxiing and ground handling condi-
tions;
(2) For the braked roll conditions of
§ 25.493 (a) and (b)(2), the drag loads on
each inflated tire may not be less than
those at each tire for the symmetrical
load distribution with no deflated tires;
(3) The vertical load factor at the
center of gravity must be 60 percent
and 50 percent, respectively, of the fac-
tor with no deflated tires, except that
it may not be less than 1g; and
(4) Pivoting need not be considered.
(f)
Towing conditions. For one and for
two deflated tires, the towing load,
F
TOW,
must be 60 percent and 50 percent,
respectively, of the load prescribed.
§ 25.519
Jacking and tie-down provi-
sions.
(a) General. The airplane must be de-
signed to withstand the limit load con-
ditions resulting from the static
ground load conditions of paragraph (b)
of this section and, if applicable, para-
graph (c) of this section at the most
critical combinations of airplane
weight and center of gravity. The max-
imum allowable load at each jack pad
must be specified.
(b) Jacking. The airplane must have
provisions for jacking and must with-
stand the following limit loads when
the airplane is supported on jacks—
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