599
Federal Aviation Administration, DOT
Pt. 25, App. G
ft
2
-sec (2.27 W/cm
2
) on the cold side of the in-
sulation specimens at a point 12 inches (30.5
cm) from the face of the test rig.
[Amdt. 25–32, 37 FR 3972, Feb. 24, 1972]
E
DITORIAL
N
OTE
: For F
EDERAL
R
EGISTER
ci-
tations affecting appendix F to Part 25, see
the List of CFR Sections Affected, which ap-
pears in the Finding Aids section of the
printed volume and at
www.fdsys.gov.
A
PPENDIX
G
TO
P
ART
25—C
ONTINUOUS
G
UST
D
ESIGN
C
RITERIA
The continuous gust design criteria in this
appendix must be used in establishing the
dynamic response of the airplane to vertical
and lateral continuous turbulence unless a
more rational criteria is used. The following
gust load requirements apply to mission
analysis and design envelope analysis:
(a) The limit gust loads utilizing the con-
tinuous turbulence concept must be deter-
mined in accordance with the provisions of
either paragraph (b) or paragraphs (c) and (d)
of this appendix.
(b)
Design envelope analysis. The limit loads
must be determined in accordance with the
following:
(1) All critical altitudes, weights, and
weight distributions, as specified in
§ 25.321(b), and all critical speeds within the
ranges indicated in paragraph (b)(3) of this
appendix must be considered.
(2) Values of A
¯ (ratio of root-mean-square
incremental load root-mean-square gust ve-
locity) must be determined by dynamic anal-
ysis. The power spectral density of the at-
mospheric turbulence must be as given by
the equation—
φ
σ
π
Ω
Ω
Ω
( )
=
+
(
)
+
(
)
[
]
2
2
2
1
8
3
1 339
1
1 339
11
6
L
L
L
/
.
.
where:
j=power-spectral density (ft./sec.)
2
/rad./ft.
s=root-mean-square gust velocity, ft./sec.
W=reduced frequency, radians per foot.
L=2,500 ft.
(3) The limit loads must be obtained by
multiplying the A
¯ values determined by the
dynamic analysis by the following values of
the gust velocity U
s
™
(i) At speed V
c
: U
s=85 fps true gust velocity
in the interval 0 to 30,000 ft. altitude and is
linearly decreased to 30 fps true gust veloc-
ity at 80,000 ft. altitude. Where the Adminis-
trator finds that a design is comparable to a
similar design with extensive satisfactory
service experience, it will be acceptable to
select U
s at V
c
less than 85 fps, but not less
than 75 fps, with linear decrease from that
value at 20,000 feet to 30 fps at 80,000 feet.
The following factors will be taken into ac-
count when assessing comparability to a
similar design:
(1) The transfer function of the new design
should exhibit no unusual characteristics as
compared to the similar design which will
significantly affect response to turbulence;
e.g., coalescence of modal response in the
frequency regime which can result in a sig-
nificant increase of loads.
(2) The typical mission of the new airplane
is substantially equivalent to that of the
similar design.
(3) The similar design should demonstrate
the adequacy of the U
s selected.
(ii) At speed V
B
: U
s is equal to 1.32 times
the values obtained under paragraph (b)(3)(i)
of this appendix.
(iii) At speed V
D
: U
s is equal to
1
⁄
2
the val-
ues obtained under paragraph (b)(3)(i) of this
appendix.
(iv) At speeds between V
B
and V
c
and be-
tween V
c
and V
D
: U
s is equal to a value ob-
tained by linear interpolation.
(4) When a stability augmentation system
is included in the analysis, the effect of sys-
tem nonlinearities on loads at the limit load
level must be realistically or conservatively
accounted for.
(c)
Mission analysis. Limit loads must be
determined in accordance with the following:
(1) The expected utilization of the airplane
must be represented by one or more flight
profiles in which the load distribution and
the variation with time of speed, altitude,
gross weight, and center of gravity position
are defined. These profiles must be divided
into mission segments or blocks, for anal-
ysis, and average or effective values of the
pertinent parameters defined for each seg-
ment.
(2) For each of the mission segments de-
fined under paragraph (c)(1) of this appendix,
values of A
¯ and N
o
must be determined by
analysis. A
¯ is defined as the ratio of root-
mean-square incremental load to root-mean-
square gust velocity and N
o
is the radius of
gyration of the load power spectral density
function about zero frequency. The power
spectral density of the atmospheric turbu-
lence must be given by the equation set forth
in paragraph (b)(2) of this appendix.
(3) For each of the load and stress quan-
tities selected, the frequency of exceedance
must be determined as a function of load
level by means of the equation—
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