Sec. 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)/7
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:
----------------------------------------------------------------------------------------------------------------
Load
Tow point Position ----------------------------------------------------
Magnitude No. Direction
----------------------------------------------------------------------------------------------------------------
Main gear.......................... ...................... 0.75 FTOW per main 1 Forward, parallel to
gear unit. 2 drag axis.
3 Forward, at 30°
4 to drag axis.
Aft, parallel to drag
axis.
Aft, at 30° to
drag axis.
Auxiliary gear..................... Swiveled forward...... 1.0 FTOW............. 5 Forward.
6 Aft.
Swiveled aft.......... ......do............. 7 Forward.
8 Aft.
Swiveled 45° from 0.5 FTOW............. 9 Forward, in plane of
forward. 10 wheel.
Aft, in plane of
wheel.
Swiveled 45° from ......do............. 11 Forward, in plane of
aft. 12 wheel.
Aft, in plane of
wheel.
----------------------------------------------------------------------------------------------------------------