(b)
With the landing gear fully extended and not in contact with the ground, a load factor of 20.0 must act on the unsprung weights of the landing gear. This load factor must act in the direction of motion of the unsprung weights as they reach theirlimitingpositionsin extending with relation to the sprungparts ofthelanding gear.
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Elodie Roux. Septembre 2003
Subpart C : Structure
FAR 25.489 : Ground handling conditions.
[Unless otherwise prescribed, the landing gear andairplane structure must be inves-tigated for the conditions in Secs. 25.491 through 25.509 with the airplane at the design ramp weight(the maximum weightforgroundhandling conditions).]No winglift maybe considered.The shock absorbersand tires may be assumed tobeintheir staticposition. Amdt. 25-23, E.. 5/8/70
FAR25.491:[Taxi,takeo. andlanding roll.]
[Within the range ofappropriate ground speeds and approved weights, the airplane structure and landing gear are assumed to be subjected to loads not less than those obtained when the aircraft is operating over the roughest ground that may reasonably be expected in normal operation.] Amdt. 25-91, E.. 7/29/97
FAR 25.493 : Braked roll conditions.
(a)
An airplane with a tail wheel is assumed to be in the level attitude with the load on themainwheels,inaccordancewith .gure6 ofAppendixA.Thelimitverticalload factor is 1.2 at the design landing weight, and 1.0 at the design takeo. weight. A drag reaction equal to the vertical reaction multiplied by a coe.cient of friction of 0.8,mustbecombined with the verticalground reactionand applied attheground 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 takeo. weight. A drag reaction equal to the vertical reaction, multiplied by a coe.cient 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 .gure 6 of Appendix A, must be considered :
(1)
Thelevel attitude with the wheels contacting theground and theloadsdistri-butedbetweenthemain and nosegear.Zeropitching accelerationis assumed.
(2)
The level attitude with only the maingear contacting theground 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 e.ective 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 arisingfrom thedynamicpitching motion of the airplanedue to sudden application of maximumbrakingforce.The airplaneis consideredtobe atdesign takeo. 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 maximumbrakingforce asdescribedinparagraphs(b) and(c) of this section.
(e)
Inthe absence of a morerational analysis,the nosegearvertical reactionprescribed in paragraph (d) of this section must be calculated according to the following formula :
WT fμAE
VN = B +
A+ BA+ B + μE
Where :
VN : Nose gear vertical reaction.
WT : Design takeo. weight.
A : Horizontal distance between the c.g. of the airplane and the nose wheel.
B :Horizontaldistancebetweenthe c.g. of the airplane and thelinejoining 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 : Coe.cient of friction of 0.80.
f : Dynamic response factor; 2.0 is to be used unless a lower factor is sub-stantiated. In the absence of other information, the dynamic response factor f may be de.ned by the (Equation 46.2, p. 549). 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：FAA规章 美国联邦航空规章 Federal Aviation Regulations 3(58)
