Sec. 25.493 - Braked roll conditions.
(a) An airplane with a tail wheel is
assumed to be in the level attitude with the load on the main wheels, in
accordance with figure 6 of appendix A. The limit vertical load factor is
1.2 at the design landing weight and 1.0 at the design ramp weight. A drag
reaction equal to the vertical reaction multiplied by a coefficient of
friction of 0.8, must be combined with the vertical ground reaction and
applied at the ground contact point.
(b) For an airplane with a nose wheel
the limit vertical load factor is 1.2 at the design landing weight, and
1.0 at the design ramp weight. A drag reaction equal to the vertical
reaction, multiplied by a coefficient of friction of 0.8, must be combined
with the vertical reaction and applied at the ground contact point of each
wheel with brakes. The following two attitudes, in accordance with figure
6 of appendix A, must be considered:
(1) The level attitude with the wheels
contacting the ground and the loads distributed between the main and nose
gear. Zero pitching acceleration is assumed.
(2) The level attitude with only the
main gear contacting the ground and with the pitching moment resisted by
angular acceleration.
(c) A drag reaction lower than that
prescribed in this section may be used if it is substantiated that an
effective drag force of 0.8 times the vertical reaction cannot be attained
under any likely loading condition.
(d) An airplane equipped with a nose
gear must be designed to withstand the loads arising from the dynamic
pitching motion of the airplane due to sudden application of maximum
braking force. The airplane is considered to be at design takeoff weight
with the nose and main gears in contact with the ground, and with a
steady-state vertical load factor of 1.0. The steady-state nose gear
reaction must be combined with the maximum incremental nose gear vertical
reaction caused by the sudden application of maximum braking force as
described in paragraphs (b) and (c) of this section.
(e) In the absence of a more rational
analysis, the nose gear vertical reaction prescribed in paragraph (d) of
this section must be calculated according to the following formula:
Where:
VN=Nose gear vertical reaction.
WT=Design takeoff weight.
A=Horizontal distance between the c.g. of the airplane
and the nose wheel.
B=Horizontal distance between the c.g. of the airplane
and the line joining the centers of the main wheels.
E=Vertical height of the c.g. of the airplane above the
ground in the 1.0 g static condition.
μ=Coefficient of friction of 0.80.
f=Dynamic response factor; 2.0 is to be used unless a
lower factor is substantiated. In the absence of other information, the
dynamic response factor f may be defined by the equation:
