505 

Federal Aviation Administration, DOT 

§ 27.521 

(2) The resultant ground loads must 

equal the vertical load specified in 
paragraph (b) of this section. 

(d) 

Sideloads in the level landing atti-

tude. 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 ob-

tained in the condition specified in 
paragraph (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 as-

sumed to be resisted by angular iner-
tia. 

(5) The skid gear must be inves-

tigated 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) of this sec-
tion. 

(2) The unbalanced moments are as-

sumed to be resisted by angular iner-
tia. 

(f) 

Special conditions. In addition to 

the conditions specified in paragraphs 
(b) and (c) of this section, the rotor-
craft must be designed for the fol-
lowing 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 re-
action load equal to one-half of the 
vertical load determined under para-
graph (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 per-

cent of the length between the skid 
tube attachments and centrally located 
midway between the skid tube attach-
ments. 

[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] 

§ 27.505

Ski landing conditions. 

If certification for ski operation is 

requested, the rotorcraft, with skis, 
must be designed to withstand the fol-
lowing loading conditions (where 

P  is 

the maximum static weight on each ski 
with the rotorcraft at design maximum 
weight, and 

n  is the limit load factor 

determined under § 27.473(b). 

(a) Up-load conditions in which— 
(1) A vertical load of 

Pn  and a hori-

zontal load of 

Pn/4 are simultaneously 

applied at the pedestal bearings; and 

(2) A vertical load of 1.33 

P is applied 

at the pedestal bearings. 

(b) A side-load condition in which a 

side load of 0.35 

Pn  is applied at the 

pedestal bearings in a horizontal plane 
perpendicular to the centerline of the 
rotorcraft. 

(c) A torque-load condition in which 

a torque load of 1.33 

P  (in foot pounds) 

is applied to the ski about the vertical 
axis through the centerline of the ped-
estal bearings. 

W

ATER

L

OADS

 

§ 27.521

Float landing conditions. 

If certification for float operation is 

requested, the rotorcraft, with floats, 
must be designed to withstand the fol-
lowing loading conditions (where the 
limit load factor is determined under 
§ 27.473(b) or assumed to be equal to 
that determined for wheel landing 
gear): 

(a) Up-load conditions in which— 
(1) A load is applied so that, with the 

rotorcraft in the static level attitude, 
the resultant water reaction passes 

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