Amdt. 27-27, E.. 10/22/90
63.4 Ground Loads
FAR 27.471 : General
(a) Loads and equilibrium. For limit ground loads–
(1)
The limitgroundloads obtained in the landing conditions in thispart must be considered to be external loads that would occur in the rotorcraft structure if it were acting as a rigidbody; and

(2)
In each speci.edlanding condition,the externalloads mustbeplacedin equi-librium with linear and angular inertia loads in a rational or conservative manner.

(b)
Critical centers of gravity. The critical centersofgravity withinthe rangefor which certi.cation is requested must be selected so that the maximum design loads are obtained in each landing gear element.

FAR 27.473 : Ground loading conditions and assumptions

(a)
[For speci.ed landing conditions, a design maximum weight must be used that is notlessthanthe maximumweight.A rotorlift maybeassumed toactthrough the center ofgravitythroughoutthelandingimpact.Thislift may not exceedtwo-thirds of the design maximum weight.

(b)
Unless otherwiseprescribed,for eachspeci.edlanding condition, the rotorcraft must be designed for a limit load factor of not less than the limit inertia load factor substantiated under Sec. 27.725.]

Amdt. 27-2, E.. 2/25/68
FAR 27.475 : Tires and shock absorbers
Unless otherwise prescribed, for each speci.ed landing condition, the tires must be assumed to bein their staticposition and the shock absorbers to be in their most critical position.
FAR 27.477 : Landing gear arrangement
Sections 27.235, 27.479 through 27.485, and 27.493 apply to landing gear with two wheels aft, and one or more wheels forward, of the center of gravity.
FAR 27.479 : Level landing conditions
(a)
Attitudes.Under each oftheloading conditionsprescribedinparagraph(b) of this section, the rotorcraft is assumed to be in each of the following level landing atti-tudes :

(1)
An attitude in which all wheels contact the ground simultaneously.

(2)
An attitudein whichthe aftwheels contact theground with theforward wheels just clear of the ground.

(b)
Loadingconditions.The rotorcraftmustbedesignedforthefollowinglandingloading conditions :

(1)
Vertical loads applied under Sec. 27.471.

(2)
The loads resulting from a combination of the loads applied under subpara-graph(1) of thisparagraph withdrag loads at each wheel of notlessthan25 percent of the vertical load at that wheel.

(3)
If there are two wheels forward, a distribution of the loads applied to those wheels under subparagraphs(1) and(2) of thisparagraphin a ratioof40 :60.

(c)
Pitching moments. Pitching moments are assumed to be resisted by–

(1)
In the case of the attitude in paragraph (a)(1) of this section, the forward landing gear; and

(2)
In the case of the attitude in paragraph (a)(2) of this section, the angular inertia forces.

′
Elodie Roux. Septembre 2003
Subpart C : Strength Requirements
FAR 27.481 : Tail-down landing conditions
(a)
The rotorcraft is assumed to be in the maximum nose-up attitude allowing ground clearance by each part of the rotorcraft.

(b)
In this attitude, ground loads are assumed to act perpendicular to the ground.

FAR 27.483 : One-wheel landing conditions
For the one-wheel landing condition, the rotorcraft is assumed to be in the level attitude and to contact the ground on one aft wheel. In this attitude–
(a)
The verticalloadmustbethe same asthat obtained onthat side underSec.27.479(b)(1); and

(b)
The unbalanced external loads must be reacted by rotorcraft inertia.

FAR 27.485 : Lateral drift landing conditions

(a)
The rotorcraft is assumed to be in the level landing attitude, with–
　
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