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:

The design maximum weight, center of gravity, and load factor must be determined under §§ 27.471 through 27.475.

Structural yielding of elastic spring members under limit loads is acceptable.

Design ultimate loads for elastic spring members need not exceed those obtained in a drop test of the gear with—

A drop height of 1.5 times that specified in § 27.725; and

An assumed rotor lift of not more than 1.5 times that used in the limit drop tests prescribed in § 27.725.

Compliance with paragraphs (b) through (e) of this section must be shown with—

The gear in its most critically deflected position for the landing condition being considered; and

The ground reactions rationally distributed along the bottom of the skid tube.

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) of this section.

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:

The vertical reactions must be combined with horizontal drag reactions of 50 percent of the vertical reaction applied at the ground.

The resultant ground loads must equal the vertical load specified in paragraph (b) of this section.

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:

The vertical ground reaction must be—

Equal to the vertical loads obtained in the condition specified in paragraph (b) of this section; and

Divided equally among the skids.

The vertical ground reactions must be combined with a horizontal sideload of 25 percent of their value.

The total sideload must be applied equally between the skids and along the length of the skids.

The unbalanced moments are assumed to be resisted by angular inertia.

The skid gear must be investigated for—

Inward acting sideloads; and

Outward acting sideloads.

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:

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) of this section.

The unbalanced moments are assumed to be resisted by angular inertia.

Special conditions. In addition to the conditions specified in paragraphs (b) and (c) of this section, the rotorcraft must be designed for the following ground reactions:

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—

Equal to 1.33 times the maximum weight;

Distributed symmetrically among the skids;

Concentrated at the forward end of the straight part of the skid tube; and

Applied only to the forward end of the skid tube and its attachment to the rotorcraft.

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) of this section. This load must be—

Applied only to the skid tube and its attachment to the rotorcraft; and

Distributed equally over 33.3 percent of the length between the skid tube attachments and centrally located midway between the skid tube attachments.