219
Federal Aviation Administration, DOT
§ 23.425
gust locks, must be designed to with-
stand the limit load conditions that
exist when the airplane is tied down
and that result from wind speeds of up
to 65 knots horizontally from any di-
rection.
[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as
amended by Amdt. 23–7, 34 FR 13089, Aug. 13,
1969; Amdt. 23–45, 58 FR 42160, Aug. 6, 1993;
Amdt. 23–48, 61 FR 5145, Feb. 9, 1996]
H
ORIZONTAL
S
TABILIZING AND
B
ALANCING
S
URFACES
§ 23.421
Balancing loads.
(a) A horizontal surface balancing
load is a load necessary to maintain
equilibrium in any specified flight con-
dition with no pitching acceleration.
(b) Horizontal balancing surfaces
must be designed for the balancing
loads occurring at any point on the
limit maneuvering envelope and in the
flap conditions specified in § 23.345.
[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as
amended by Amdt. 23–7, 34 FR 13089, Aug. 13,
1969; Amdt. 23–42, 56 FR 352, Jan. 3, 1991]
§ 23.423
Maneuvering loads.
Each horizontal surface and its sup-
porting structure, and the main wing
of a canard or tandem wing configura-
tion, if that surface has pitch control,
must be designed for the maneuvering
loads imposed by the following condi-
tions:
(a) A sudden movement of the pitch-
ing control, at the speed V
A
, to the
maximum aft movement, and the max-
imum forward movement, as limited by
the control stops, or pilot effort,
whichever is critical.
(b) A sudden aft movement of the
pitching control at speeds above V
A
,
followed by a forward movement of the
pitching control resulting in the fol-
lowing combinations of normal and an-
gular acceleration:
Condition
Normal
accelera-
tion (n)
Angular acceleration
(radian/sec
2
)
Nose-up pitching ........
1.0
+39n
m
÷
V
×
(n
m
¥
1.5)
Nose-down pitching ....
n
m
¥
39n
m
÷
V
×
(n
m
¥
1.5)
where—
(1) n
m
=positive limit maneuvering
load factor used in the design of the
airplane; and
(2) V=initial speed in knots.
The conditions in this paragraph in-
volve loads corresponding to the loads
that may occur in a ‘‘checked maneu-
ver’’ (a maneuver in which the pitching
control is suddenly displaced in one di-
rection and then suddenly moved in the
opposite direction). The deflections and
timing of the ‘‘checked maneuver’’
must avoid exceeding the limit maneu-
vering load factor. The total horizontal
surface load for both nose-up and nose-
down pitching conditions is the sum of
the balancing loads at
V and the speci-
fied value of the normal load factor
n,
plus the maneuvering load increment
due to the specified value of the angu-
lar acceleration.
[Amdt. 23–42, 56 FR 353, Jan. 3, 1991; 56 FR
5455, Feb. 11, 1991]
§ 23.425
Gust loads.
(a) Each horizontal surface, other
than a main wing, must be designed for
loads resulting from—
(1) Gust velocities specified in
§ 23.333(c) with flaps retracted; and
(2) Positive and negative gusts of 25
f.p.s. nominal intensity at
V
F
cor-
responding to the flight conditions
specified in § 23.345(a)(2).
(b) [Reserved]
(c) When determining the total load
on the horizontal surfaces for the con-
ditions specified in paragraph (a) of
this section, the initial balancing loads
for steady unaccelerated flight at the
pertinent design speeds V
F
, V
C
, and V
D
must first be determined. The incre-
mental load resulting from the gusts
must be added to the initial balancing
load to obtain the total load.
(d) In the absence of a more rational
analysis, the incremental load due to
the gust must be computed as follows
only on airplane configurations with
aft-mounted, horizontal surfaces, un-
less its use elsewhere is shown to be
conservative:
Δ
L
K U Va S
498
ht
g
de
ht
ht
=
−
⎛
⎝⎜
⎞
⎠⎟
1
d
d
ε
α
where—
DL
ht
=Incremental horizontal tailload (lbs.);
K
g
=Gust alleviation factor defined in § 23.341;
U
de
=Derived gust velocity (f.p.s.);
V=Airplane equivalent speed (knots);
a
ht
=Slope of aft horizontal lift curve (per ra-
dian)
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