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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.




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

...................


Forward. 
Aft. 

Swiveled aft ............................

......do .......................


Forward. 
Aft. 

Swiveled 45

° 

from forward .....

0.5 F

TOW

...................

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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