415
Federal Aviation Administration, DOT
§ 25.509
§ 25.503
Pivoting.
(a) The airplane is assumed to pivot
about one side of the main gear with
the brakes on that side locked. The
limit vertical load factor must be 1.0
and the coefficient of friction 0.8.
(b) The airplane is assumed to be in
static equilibrium, with the loads being
applied at the ground contact points,
in accordance with figure 8 of appendix
A.
§ 25.507
Reversed braking.
(a) The airplane must be in a three
point static ground attitude. Hori-
zontal reactions parallel to the ground
and directed forward must be applied
at the ground contact point of each
wheel with brakes. The limit loads
must be equal to 0.55 times the vertical
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]
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