Section 27.171

14 CFR Ch. I (1-1-19 Edition)

Section 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.
Section 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 altitude for which certification is requested, with the throttle and collective pitch held constant during the maneuvers specified in Section 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 airspeed curve may be neutral or negative
if the rotorcraft possesses flight characteristics that allow the pilot to
maintain airspeed within Section5 knots of
the desired trim airspeed without exceptional piloting skill or alertness.

spaschal on DSK3GDR082PROD with CFR

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

Section 27.175 Demonstration of static longitudinal stability.
(a) Climb. Static longitudinal stability must be shown in the climb condition at speeds from Vy Section 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 VY.
(b) Cruise. Static longitudinal stability must be shown in the cruise condition at speeds from 0.8 VNE Section 10 kt to
0.8 VNE + 10 kt or, if VH is less than 0.8
VNE, from VH Section10 kt to VH + 10 kt,
with - 
(1) Critical weight;
(2) Critical center of gravity;
(3) Power for level flight at 0.8 VNE or
VH, whichever is less;

(4) The landing gear retracted; and
(5) The rotorcraft trimmed at 0.8 VNE
or VH, whichever is less.
(c) VNE. Static longitudinal stability
must be shown at speeds from VNE Section 20
kt to VNE with - 
(1) Critical weight;
(2) Critical center of gravity;
(3) Power required for level flight at
VNE Section10 kt or maximum continuous
power, whichever is less;
(4) The landing gear retracted; and
(5) The rotorcraft trimmed at VNE Section
10 kt.
(d) Autorotation. Static longitudinal
stability must be shown in autorotation at - 
(1) Airspeeds from the minimum rate
of descent airspeedSection10 kt to the minimum 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
airspeedSection10 kt to the best angle-ofglide 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 Federal 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]

Section 27.177 Static directional stability.
(a) The directional controls must operate in such a manner that the sense
and direction of motion of the rotorcraft following control displacement
are in the direction of the pedal motion
with the throttle and collective controls held constant at the trim conditions specified in Section 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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