403
Federal Aviation Administration, DOT
§ 25.341
(1) May not be less than ¥1.0 at
speeds up to
V
C
; and
(2) Must vary linearly with speed
from the value at
V
C
to zero at
V
D.
(d) Maneuvering load factors lower
than those specified in this section
may be used if the airplane has design
features that make it impossible to ex-
ceed these values in flight.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5672, Apr. 8,
1970]
§ 25.341
Gust and turbulence loads.
(a)
Discrete Gust Design Criteria. The
airplane is assumed to be subjected to
symmetrical vertical and lateral gusts
in level flight. Limit gust loads must
be determined in accordance with the
provisions:
(1) Loads on each part of the struc-
ture must be determined by dynamic
analysis. The analysis must take into
account unsteady aerodynamic charac-
teristics and all significant structural
degrees of freedom including rigid body
motions.
(2) The shape of the gust must be:
U
U
ds
=
⎛
⎝⎜
⎞
⎠⎟
⎡
⎣
⎢
⎤
⎦
⎥
2
1- Cos
s
H
π
for 0
≤
s
≤
2H
where—
s=distance penetrated into the gust (feet);
U
ds
=the design gust velocity in equivalent
airspeed specified in paragraph (a)(4) of
this section; and
H=the gust gradient which is the distance
(feet) parallel to the airplane’s flight
path for the gust to reach its peak veloc-
ity.
(3) A sufficient number of gust gra-
dient distances in the range 30 feet to
350 feet must be investigated to find
the critical response for each load
quantity.
(4) The design gust velocity must be:
U
U
F H
ds
ref g
=
(
)
350
1 6
where—
U
ref
=the reference gust velocity in equivalent
airspeed defined in paragraph (a)(5) of
this section.
F
g
=the flight profile alleviation factor de-
fined in paragraph (a)(6) of this section.
(5) The following reference gust ve-
locities apply:
(i) At the airplane design speed V
C
:
Positive and negative gusts with ref-
erence gust velocities of 56.0 ft/sec EAS
must be considered at sea level. The
reference gust velocity may be reduced
linearly from 56.0 ft/sec EAS at sea
level to 44.0 ft/sec EAS at 15000 feet.
The reference gust velocity may be fur-
ther reduced linearly from 44.0 ft/sec
EAS at 15000 feet to 26.0 ft/sec EAS at
50000 feet.
(ii) At the airplane design speed V
D
:
The reference gust velocity must be 0.5
times the value obtained under
§ 25.341(a)(5)(i).
(6) The flight profile alleviation fac-
tor, F
g
, must be increased linearly from
the sea level value to a value of 1.0 at
the maximum operating altitude de-
fined in § 25.1527. At sea level, the flight
profile alleviation factor is determined
by the following equation:
F
F
F
Where
F
Z
F
R Tan
R
R
Maximum Landing Weight
Maximum Take off Weight
R
Maximum Zero Fuel Weight
Maximum Take off Weight
g
gz
gm
gz
mo
gm
=
+
(
)
= −
=
⎛
⎝
⎞
⎠
=
=
0 5
1
250000
4
2
1
1
2
.
:
;
;
;
;
π
-
-
Z
mo
=Maximum operating altitude defined in
§ 25.1527.
(7) When a stability augmentation
system is included in the analysis, the
effect of any significant system non-
linearities should be accounted for
when deriving limit loads from limit
gust conditions.
(b)
Continuous Gust Design Criteria.
The dynamic response of the airplane
to vertical and lateral continuous tur-
bulence must be taken into account.
The continuous gust design criteria of
appendix G of this part must be used to
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