---
kind: "section"
citation: "14 C.F.R. § 27.501"
title: "14"
number: "27.501"
heading: "Ground loading conditions: landing gear with skids."
url: "https://uscodex.org/cfr/14/27.501"
---

# §27.501. Ground loading conditions: landing gear with skids.

- (a) **General.** Rotorcraft with landing gear with skids must be designed for the loading conditions specified in this section. In showing compliance with this section, the following apply:
  - (1) The design maximum weight, center of gravity, and load factor must be determined under [§§ 27.471 through 27.475](/cfr/14/27.471..27.475.md).
  - (2) **Structural yielding of elastic spring members under limit loads is acceptable.**
  - (3) Design ultimate loads for elastic spring members need not exceed those obtained in a drop test of the gear with—
    - (i) A drop height of 1.5 times that specified in [§ 27.725](/cfr/14/27.725.md); and
    - (ii) An assumed rotor lift of not more than 1.5 times that used in the limit drop tests prescribed in [§ 27.725](/cfr/14/27.725.md).
  - (4) Compliance with [paragraphs (b) through (e)](#b..e) of this section must be shown with—
    - (i) The gear in its most critically deflected position for the landing condition being considered; and
    - (ii) **The ground reactions rationally distributed along the bottom of the skid tube.**
- (b) **Vertical reactions in the level landing attitude.** In the level attitude, and with the rotorcraft contacting the ground along the bottom of both skids, the vertical reactions must be applied as prescribed in [paragraph (a)](#a) of this section.
- (c) **Drag reactions in the level landing attitude.** In the level attitude, and with the rotorcraft contacting the ground along the bottom of both skids, the following apply:
  - (1) The vertical reactions must be combined with horizontal drag reactions of 50 percent of the vertical reaction applied at the ground.
  - (2) The resultant ground loads must equal the vertical load specified in [paragraph (b)](#b) of this section.
- (d) **Sideloads in the level landing attitude.** In the level attitude,and with the rotorcraft contacting the ground along the bottom of both skids, the following apply:
  - (1) The vertical ground reaction must be—
    - (i) Equal to the vertical loads obtained in the condition specified in [paragraph (b)](#b) of this section; and
    - (ii) **Divided equally among the skids.**
  - (2) The vertical ground reactions must be combined with a horizontal sideload of 25 percent of their value.
  - (3) The total sideload must be applied equally between the skids and along the length of the skids.
  - (4) **The unbalanced moments are assumed to be resisted by angular inertia.**
  - (5) The skid gear must be investigated for—
    - (i) Inward acting sideloads; and
    - (ii) **Outward acting sideloads.**
- (e) **One-skid landing loads in the level attitude.** In the level attitude, and with the rotorcraft contacting the ground along the bottom of one skid only, the following apply:
  - (1) The vertical load on the ground contact side must be the same as that obtained on that side in the condition specified in [paragraph (b)](#b) of this section.
  - (2) **The unbalanced moments are assumed to be resisted by angular inertia.**
- (f) **Special conditions.** In addition to the conditions specified in paragraphs [(b)](#b) and [(c)](#c) of this section, the rotorcraft must be designed for the following ground reactions:
  - (1) A ground reaction load acting up and aft at an angle of 45 degrees to the longitudinal axis of the rotorcraft. This load must be—
    - (i) Equal to 1.33 times the maximum weight;
    - (ii) Distributed symmetrically among the skids;
    - (iii) Concentrated at the forward end of the straight part of the skid tube; and
    - (iv) **Applied only to the forward end of the skid tube and its attachment to the rotorcraft.**
  - (2) With the rotorcraft in the level landing attitude, a vertical ground reaction load equal to one-half of the vertical load determined under [paragraph (b)](#b) of this section. This load must be—
    - (i) Applied only to the skid tube and its attachment to the rotorcraft; and
    - (ii) Distributed equally over 33.3 percent of the length between the skid tube attachments and centrally located midway between the skid tube attachments.

## Notes

### Amendments

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as amended by Amdt. 27-2, 33 FR 963, Jan. 26, 1968; Amdt. 27-26, 55 FR 8000, Mar. 6, 1990]

### Authority

Authority: 49 U.S.C. 106(f), 106(g), 40113, 44701-44702, 44704.

### Source

Source: Docket No. 5074, 29 FR 15695, Nov. 24, 1964, unless otherwise noted.

### Amendments

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as amended by Amdt. 27-2, 33 FR 963, Jan. 26, 1968; Amdt. 27-26, 55 FR 8000, Mar. 6, 1990]