Federal Aviation Administration, DOT

Section 25.509

unbalanced yawing moments assumed
to be resisted by airplane inertia
forces.
(d) For other than the nose gear, its
attaching structure, and the forward
fuselage structure, the loading conditions are those prescribed in paragraph
(b) of this section, except that - 
(1) A lower drag reaction may be used
if an effective drag force of 0.8 times
the vertical reaction cannot be reached
under any likely loading condition; and
(2) The forward acting load at the
center of gravity need not exceed the
maximum drag reaction on one main
gear, determined in accordance with
Section 25.493(b).
(e) With the airplane at design ramp
weight, and the nose gear in any steerable position, the combined application
of full normal steering torque and
vertical force equal to 1.33 times the
maximum static reaction on the nose
gear must be considered in designing
the nose gear, its attaching structure,
and the forward fuselage structure.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-23, 35 FR 5673, Apr. 8,
1970; Amdt. 25-46, 43 FR 50595, Oct. 30, 1978;
Amdt. 25-91, 62 FR 40705, July 29, 1997]

spaschal on DSK3GDR082PROD with CFR

Section 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.
Section 25.507 Reversed braking.
(a) The airplane must be in a three
point static ground attitude. Horizontal 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 developed by 1.2 times the nominal maximum 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.
Section 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 WT as the design ramp
weight, the towing load, FTOW, is - 
(i) 0.3 WT for WT less than 30,000
pounds;
(ii) (6WT + 450,000)/70 for WT between
30,000 and 100,000 pounds; and
(iii) 0.15 WT for WT over 100,000
pounds.
(b) For towing points not on the
landing gear but near the plane of symmetry 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 components specified for the main gear apply.
Where the specified angle of swivel
cannot be reached, the maximum obtainable 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 applied.
(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 airplane inertia to achieve equilibrium
must be applied.
(ii) The loads must be reacted by airplane inertia.
(d) The prescribed towing loads are as
follows:

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