255
Federal Aviation Administration, DOT
§ 25.527
(1) For jacking by the landing gear at
the maximum ramp weight of the air-
plane, the airplane structure must be
designed for a vertical load of 1.33
times the vertical static reaction at
each jacking point acting singly and in
combination with a horizontal load of
0.33 times the vertical static reaction
applied in any direction.
(2) For jacking by other airplane
structure at maximum approved jack-
ing weight:
(i) The airplane structure must be de-
signed for a vertical load of 1.33 times
the vertical reaction at each jacking
point acting singly and in combination
with a horizontal load of 0.33 times the
vertical static reaction applied in any
direction.
(ii) The jacking pads and local struc-
ture must be designed for a vertical
load of 2.0 times the vertical static re-
action at each jacking point, acting
singly and in combination with a hori-
zontal load of 0.33 times the vertical
static reaction applied in any direc-
tion.
(c) Tie-down. If tie-down points are
provided, the main tie-down points and
local structure must withstand the
limit loads resulting from a 65-knot
horizontal wind from any direction.
[Doc. No. 26129, 59 FR 22102, Apr. 28, 1994]
W
ATER
L
OADS
§ 25.521
General.
(a) Seaplanes must be designed for
the water loads developed during take-
off and landing, with the seaplane in
any attitude likely to occur in normal
operation, and at the appropriate for-
ward and sinking velocities under the
most severe sea conditions likely to be
encountered.
(b) Unless a more rational analysis of
the water loads is made, or the stand-
ards in ANC–3 are used, §§ 25.523
through 25.537 apply.
(c) The requirements of this section
and §§ 25.523 through 25.537 apply also to
amphibians.
§ 25.523
Design weights and center of
gravity positions.
(a)
Design weights. The water load re-
quirements must be met at each oper-
ating weight up to the design landing
weight except that, for the takeoff con-
dition prescribed in § 25.531, the design
water takeoff weight (the maximum
weight for water taxi and takeoff run)
must be used.
(b)
Center of gravity positions. The
critical centers of gravity within the
limits for which certification is re-
quested must be considered to reach
maximum design loads for each part of
the seaplane structure.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5673, Apr. 8,
1970]
§ 25.525
Application of loads.
(a) Unless otherwise prescribed, the
seaplane as a whole is assumed to be
subjected to the loads corresponding to
the load factors specified in § 25.527.
(b) In applying the loads resulting
from the load factors prescribed in
§ 25.527, the loads may be distributed
over the hull or main float bottom (in
order to avoid excessive local shear
loads and bending moments at the lo-
cation of water load application) using
pressures not less than those pre-
scribed in § 25.533(c).
(c) For twin float seaplanes, each
float must be treated as an equivalent
hull on a fictitious seaplane with a
weight equal to one-half the weight of
the twin float seaplane.
(d) Except in the takeoff condition of
§ 25.531, the aerodynamic lift on the
seaplane during the impact is assumed
to be
2
⁄
3
of the weight of the seaplane.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Doc. No. FAA–2022–1355, Amdt.
25–148, 87 FR 75710, Dec. 9, 2022; 88 FR 2813,
Jan. 18, 2023]
§ 25.527
Hull and main float load fac-
tors.
(a) Water reaction load factors
n
W
must be computed in the following
manner:
(1) For the step landing case
n
C V
W
w
S
=
⎛
⎝
⎞
⎠
1
0
2
2
3
1
3
Tan
β
(2) For the bow and stern landing
cases
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256
14 CFR Ch. I (1–1–24 Edition)
§ 25.529
n
C V
W
K
r
w
S
x
=
⎛
⎝
⎞
⎠
×
+
(
)
1
0
1
2
2
2
3
1
3
2
3
1
Tan
β
(b) The following values are used:
(1)
n
W
= water reaction load factor
(that is, the water reaction divided by
seaplane weight).
(2)
C
1
= empirical seaplane operations
factor equal to 0.012 (except that this
factor may not be less than that nec-
essary to obtain the minimum value of
step load factor of 2.33).
(3)
V
S0
= seaplane stalling speed in
knots with flaps extended in the appro-
priate landing position and with no
slipstream effect.
(4)
b
= angle of dead rise at the longi-
tudinal station at which the load fac-
tor is being determined in accordance
with figure 1 of appendix B.
(5)
W=
seaplane design landing
weight in pounds.
(6)
K
1
= empirical hull station weigh-
ing factor, in accordance with figure 2
of appendix B.
(7)
r
x
= ratio of distance, measured
parallel to hull reference axis, from the
center of gravity of the seaplane to the
hull longitudinal station at which the
load factor is being computed to the ra-
dius of gyration in pitch of the sea-
plane, the hull reference axis being a
straight line, in the plane of sym-
metry, tangential to the keel at the
main step.
(c) For a twin float seaplane, because
of the effect of flexibility of the attach-
ment of the floats to the seaplane, the
factor
K
1
may be reduced at the bow
and stern to 0.8 of the value shown in
figure 2 of appendix B. This reduction
applies only to the design of the carry-
through and seaplane structure.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5673, Apr. 8,
1970]
§ 25.529
Hull and main float landing
conditions.
(a)
Symmetrical step, bow, and stern
landing. For symmetrical step, bow,
and stern landings, the limit water re-
action load factors are those computed
under § 25.527. In addition—
(1) For symmetrical step landings,
the resultant water load must be ap-
plied at the keel, through the center of
gravity, and must be directed per-
pendicularly to the keel line;
(2) For symmetrical bow landings,
the resultant water load must be ap-
plied at the keel, one-fifth of the longi-
tudinal distance from the bow to the
step, and must be directed perpendicu-
larly to the keel line; and
(3) For symmetrical stern landings,
the resultant water load must be ap-
plied at the keel, at a point 85 percent
of the longitudinal distance from the
step to the stern post, and must be di-
rected perpendicularly to the keel line.
(b)
Unsymmetrical landing for hull and
single float seaplanes. Unsymmetrical
step, bow, and stern landing conditions
must be investigated. In addition—
(1) The loading for each condition
consists of an upward component and a
side component equal, respectively, to
0.75 and 0.25 tan
b
times the resultant
load in the corresponding symmetrical
landing condition; and
(2) The point of application and di-
rection of the upward component of the
load is the same as that in the sym-
metrical condition, and the point of ap-
plication of the side component is at
the same longitudinal station as the
upward component but is directed in-
ward perpendicularly to the plane of
symmetry at a point midway between
the keel and chine lines.
(c)
Unsymmetrical landing; twin float
seaplanes. The unsymmetrical loading
consists of an upward load at the step
of each float of 0.75 and a side load of
0.25 tan
b
at one float times the step
landing load reached under § 25.527. The
side load is directed inboard, per-
pendicularly to the plane of symmetry
midway between the keel and chine
lines of the float, at the same longitu-
dinal station as the upward load.
§ 25.531
Hull and main float takeoff
condition.
For the wing and its attachment to
the hull or main float—
(a) The aerodynamic wing lift is as-
sumed to be zero; and
(b) A downward inertia load, cor-
responding to a load factor computed
from the following formula, must be
applied:
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