497 

Federal Aviation Administration, DOT 

§ 27.177 

§ 27.171

Stability: general. 

The rotorcraft must be able to be 

flown, without undue pilot fatigue or 
strain, in any normal maneuver for a 
period of time as long as that expected 
in normal operation. At least three 
landings and takeoffs must be made 
during this demonstration. 

§ 27.173

Static longitudinal stability. 

(a) The longitudinal control must be 

designed so that a rearward movement 
of the control is necessary to obtain an 
airspeed less than the trim speed, and a 
forward movement of the control is 
necessary to obtain an airspeed more 
than the trim speed. 

(b) Throughout the full range of alti-

tude for which certification is re-
quested, with the throttle and collec-
tive pitch held constant during the ma-
neuvers specified in § 27.175(a) through 
(d), the slope of the control position 
versus airspeed curve must be positive. 
However, in limited flight conditions 
or modes of operation determined by 
the Administrator to be acceptable, the 
slope of the control position versus air-
speed curve may be neutral or negative 
if the rotorcraft possesses flight char-
acteristics that allow the pilot to 
maintain airspeed within 

±

5 knots of 

the desired trim airspeed without ex-
ceptional piloting skill or alertness. 

[Amdt. 27–21, 49 FR 44433, Nov. 6, 1984, as 
amended by Amdt. 27–44, 73 FR 10999, Feb. 29, 
2008] 

§ 27.175

Demonstration of static longi-

tudinal stability. 

(a) 

Climb.  Static longitudinal sta-

bility must be shown in the climb con-
dition at speeds from Vy 

¥ 

10 kt to Vy 

+ 10 kt with— 

(1) Critical weight; 
(2) Critical center of gravity; 
(3) Maximum continuous power; 
(4) The landing gear retracted; and 
(5) The rotorcraft trimmed at 

V

Y.

 

(b) 

Cruise.  Static longitudinal sta-

bility must be shown in the cruise con-
dition at speeds from 0.8 V

NE

¥ 

10 kt to 

0.8 V

NE

+ 10 kt or, if V

H

is less than 0.8 

V

NE

, from V

H

¥

10 kt to V

H

+ 10 kt, 

with— 

(1) Critical weight; 
(2) Critical center of gravity; 
(3) Power for level flight at 0.8 V

NE

or 

V

H

, whichever is less; 

(4) The landing gear retracted; and 
(5) The rotorcraft trimmed at 0.8 V

NE

 

or V

H

, whichever is less. 

(c) 

V

NE.

Static longitudinal stability 

must be shown at speeds from V

NE

¥ 

20 

kt to V

NE

with— 

(1) Critical weight; 
(2) Critical center of gravity; 
(3) Power required for level flight at 

V

NE

¥

10 kt or maximum continuous 

power, whichever is less; 

(4) The landing gear retracted; and 
(5) The rotorcraft trimmed at V

NE

¥ 

10 kt. 

(d) 

Autorotation.  Static longitudinal 

stability must be shown in autorota-
tion at— 

(1) Airspeeds from the minimum rate 

of descent airspeed

¥

10 kt to the min-

imum rate of descent airspeed + 10 kt, 
with— 

(i) Critical weight; 
(ii) Critical center of gravity; 
(iii) The landing gear extended; and 
(iv) The rotorcraft trimmed at the 

minimum rate of descent airspeed. 

(2) Airspeeds from best angle-of-glide 

airspeed

¥

10 kt to the best angle-of- 

glide airspeed + 10 kt, with— 

(i) Critical weight; 
(ii) Critical center of gravity; 
(iii) The landing gear retracted; and 
(iv) The rotorcraft trimmed at the 

best angle-of-glide airspeed. 

(Secs. 313(a), 601, 603, 604, and 605 of the Fed-
eral Aviation Act of 1958 (49 U.S.C. 1354(a), 
1421, 1423, 1424, and 1425); and sec. 6(c) of the 
Dept. of Transportation Act (49 U.S.C. 
1655(c))) 

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as 
amended by Amdt. 27–2, 33 FR 963, Jan. 26, 
1968; Amdt. 27–11, 41 FR 55468, Dec. 20, 1976; 
Amdt. 27–14, 43 FR 2325, Jan. 16, 1978; Amdt. 
27–21, 49 FR 44433, Nov. 6, 1984; Amdt. 27–34, 62 
FR 46173, Aug. 29, 1997; Amdt. 27–44, 73 FR 
10999, Feb. 29, 2008] 

§ 27.177

Static directional stability. 

(a) The directional controls must op-

erate in such a manner that the sense 
and direction of motion of the rotor-
craft following control displacement 
are in the direction of the pedal motion 
with the throttle and collective con-
trols held constant at the trim condi-
tions specified in § 27.175(a), (b), and (c). 
Sideslip angles must increase with 
steadily increasing directional control 
deflection for sideslip angles up to the 
lesser of— 

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