---
kind: "range"
citation: "14 C.F.R. §§ 27.471–27.485"
title: "14"
from: "27.471"
to: "27.485"
count: 8
url: "https://uscodex.org/cfr/14/27.471..27.485"
---

# §27.471. General.

- (a) **Loads and equilibrium.** For limit ground loads—
  - (1) The limit ground loads obtained in the landing conditions in this part must be considered to be external loads that would occur in the rotorcraft structure if it were acting as a rigid body; and
  - (2) In each specified landing condition, the external loads must be placed in equilibrium with linear and angular inertia loads in a rational or conservative manner.
- (b) **Critical centers of gravity.** The critical centers of gravity within the range for which certification is requested must be selected so that the maximum design loads are obtained in each landing gear element.

# §27.473. Ground loading conditions and assumptions.

- (a) For specified landing conditions, a design maximum weight must be used that is not less than the maximum weight. A rotor lift may be assumed to act through the center of gravity throughout the landing impact. This lift may not exceed two-thirds of the design maximum weight.
- (b) Unless otherwise prescribed, for each specified landing condition, the rotorcraft must be designed for a limit load factor of not less than the limit inertia load factor substantiated under [§ 27.725](/cfr/14/27.725.md).

# §27.475. Tires and shock absorbers.


Unless otherwise prescribed, for each specified landing condition, the tires must be assumed to be in their static position and the shock absorbers to be in their most critical position.


# §27.477. Landing gear arrangement.


Sections [27.235](/cfr/14/27.235.md), [27.479 through 27.485](/cfr/14/27.479..27.485.md), and [27.493](/cfr/14/27.493.md) apply to landing gear with two wheels aft, and one or more wheels forward, of the center of gravity.


# §27.479. Level landing conditions.

- (a) **Attitudes.** Under each of the loading conditions prescribed in [paragraph (b)](#b) of this section, the rotorcraft is assumed to be in each of the following level landing attitudes:
  - (1) **An attitude in which all wheels contact the ground simultaneously.**
  - (2) An attitude in which the aft wheels contact the ground with the forward wheels just clear of the ground.
- (b) **Loading conditions.** The rotorcraft must be designed for the following landing loading conditions:
  - (1) Vertical loads applied under [§ 27.471](/cfr/14/27.471.md).
  - (2) The loads resulting from a combination of the loads applied under [paragraph (b)(1)](#b-1) of this section with drag loads at each wheel of not less than 25 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 paragraphs [(b)(1)](#b-1) and [(2)](#b-2) of this section in a ratio of 40:60.
- (c) **Pitching moments.** Pitching moments are assumed to be resisted by—
  - (1) In the case of the attitude in [paragraph (a)(1)](#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.**

# §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.**

# §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 vertical load must be the same as that obtained on that side under [§ 27.479(b)(1)](/cfr/14/27.479.md?p=b-1); and
- (b) The unbalanced external loads must be reacted by rotorcraft inertia.

# §27.485. Lateral drift landing conditions.

- (a) **The rotorcraft is assumed to be in the level landing attitude, with—**
  - (1) Side loads combined with one-half of the maximum ground reactions obtained in the level landing conditions of [§ 27.479 (b)(1)](/cfr/14/27.479.md?p=b-1); and
  - (2) **The loads obtained under paragraph (a)(1) of this section applied—**
    - (i) At the ground contact point; or
    - (ii) **For full-swiveling gear, at the center of the axle.**
- (b) The rotorcraft must be designed to withstand, at ground contact—
  - (1) When only the aft wheels contact the ground, side loads of 0.8 times the vertical reaction acting inward on one side, and 0.6 times the vertical reaction acting outward on the other side, all combined with the vertical loads specified in [paragraph (a)](#a) of this section; and
  - (2) **When all wheels contact the ground simultaneously—**
    - (i) For the aft wheels, the side loads specified in [paragraph (b)(1)](#b-1) of this section; and
    - (ii) For the forward wheels, a side load of 0.8 times the vertical reaction combined with the vertical load specified in [paragraph (a)](#a) of this section.