257
Federal Aviation Administration, DOT
§ 25.533
n
C
V
W
TO
S
=
⎛
⎝
⎞
⎠
1
2
2
3
1
3
tan
β
where—
n = inertia load factor;
C
TO
= empirical seaplane operations factor
equal to 0.004;
V
S1
= seaplane stalling speed (knots) at the
design takeoff weight with the flaps ex-
tended in the appropriate takeoff posi-
tion;
b
= angle of dead rise at the main step (de-
grees); and
W = design water takeoff weight in pounds.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5673, Apr. 8,
1970]
§ 25.533
Hull and main float bottom
pressures.
(a)
General. The hull and main float
structure, including frames and bulk-
heads, stringers, and bottom plating,
must be designed under this section.
(b)
Local pressures. For the design of
the bottom plating and stringers and
their attachments to the supporting
structure, the following pressure dis-
tributions must be applied:
(1) For an unflared bottom, the pres-
sure at the chine is 0.75 times the pres-
sure at the keel, and the pressures be-
tween the keel and chine vary linearly,
in accordance with figure 3 of appendix
B. The pressure at the keel (psi) is
computed as follows:
P
C
K V
k
S
k
=
×
2
2
1
2
tan
β
where—
P
k
= pressure (p.s.i.) at the keel;
C
2
= 0.00213;
K
2
= hull station weighing factor, in accord-
ance with figure 2 of appendix B;
V
S1
= seaplane stalling speed (Knots) at the
design water takeoff weight with flaps
extended in the appropriate takeoff posi-
tion; and
b
K
= angle of dead rise at keel, in accordance
with figure 1 of appendix B.
(2) For a flared bottom, the pressure
at the beginning of the flare is the
same as that for an unflared bottom,
and the pressure between the chine and
the beginning of the flare varies lin-
early, in accordance with figure 3 of ap-
pendix B. The pressure distribution is
the same as that prescribed in para-
graph (b)(1) of this section for an
unflared bottom except that the pres-
sure at the chine is computed as fol-
lows:
P
C
K V
ch
S
=
×
3
2
1
2
tan
β
where—
P
ch
= pressure (p.s.i.) at the chine;
C
3
= 0.0016;
K
2
= hull station weighing factor, in accord-
ance with figure 2 of appendix B;
V
S1
= seaplane stalling speed at the design
water takeoff weight with flaps extended
in the appropriate takeoff position; and
b
= angle of dead rise at appropriate station.
The area over which these pressures
are applied must simulate pressures oc-
curring during high localized impacts
on the hull or float, but need not ex-
tend over an area that would induce
critical stresses in the frames or in the
overall structure.
(c)
Distributed pressures. For the de-
sign of the frames, keel, and chine
structure, the following pressure dis-
tributions apply:
(1) Symmetrical pressures are com-
puted as follows:
P
C
K V
S
=
×
4
2
0
2
tan
β
where—
P = pressure (p.s.i.);
C
4
= 0.078
C
1
(with
C
1
computed under
§ 25.527);
K
2
= hull station weighing factor, deter-
mined in accordance with figure 2 of ap-
pendix B;
V
S0
= seaplane stalling speed (Knots) with
landing flaps extended in the appropriate
position and with no slipstream effect;
and
V
S0
= seaplane stalling speed with landing
flaps extended in the appropriate posi-
tion and with no slipstream effect; and
b
= angle of dead rise at appropriate sta-
tion.
(2) The unsymmetrical pressure dis-
tribution consists of the pressures pre-
scribed in paragraph (c)(1) of this sec-
tion on one side of the hull or main
float centerline and one-half of that
pressure on the other side of the hull or
main float centerline, in accordance
with figure 3 of appendix B.
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258
14 CFR Ch. I (1–1–24 Edition)
§ 25.535
These pressures are uniform and must
be applied simultaneously over the en-
tire hull or main float bottom. The
loads obtained must be carried into the
sidewall structure of the hull proper,
but need not be transmitted in a fore
and aft direction as shear and bending
loads.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–23, 35 FR 5673, Apr. 8,
1970]
§ 25.535
Auxiliary float loads.
(a)
General. Auxiliary floats and their
attachments and supporting structures
must be designed for the conditions
prescribed in this section. In the cases
specified in paragraphs (b) through (e)
of this section, the prescribed water
loads may be distributed over the float
bottom to avoid excessive local loads,
using bottom pressures not less than
those prescribed in paragraph (g) of
this section.
(b)
Step loading. The resultant water
load must be applied in the plane of
symmetry of the float at a point three-
fourths of the distance from the bow to
the step and must be perpendicular to
the keel. The resultant limit load is
computed as follows, except that the
value of
L need not exceed three times
the weight of the displaced water when
the float is completely submerged:
L
C V
W
r
S
s
y
=
+
(
)
5
2
0
2
2
3
2
3
2
3
1
tan
β
where—
L = limit load (lbs.);
C
5
= 0.0053;
V
S0
= seaplane stalling speed (knots) with
landing flaps extended in the appropriate
position and with no slipstream effect;
W = seaplane design landing weight in
pounds;
b
S
= angle of dead rise at a station
3
⁄
4
of the
distance from the bow to the step, but
need not be less than 15 degrees; and
r
y
= ratio of the lateral distance between the
center of gravity and the plane of sym-
metry of the float to the radius of gyra-
tion in roll.
(c)
Bow loading. The resultant limit
load must be applied in the plane of
symmetry of the float at a point one-
fourth of the distance from the bow to
the step and must be perpendicular to
the tangent to the keel line at that
point. The magnitude of the resultant
load is that specified in paragraph (b)
of this section.
(d)
Unsymmetrical step loading. The re-
sultant water load consists of a compo-
nent equal to 0.75 times the load speci-
fied in paragraph (a) of this section and
a side component equal to 0.25 tan
b
times the load specified in paragraph
(b) of this section. The side load must
be applied perpendicularly to the plane
of symmetry of the float at a point
midway between the keel and the
chine.
(e)
Unsymmetrical bow loading. The re-
sultant water load consists of a compo-
nent equal to 0.75 times the load speci-
fied in paragraph (b) of this section and
a side component equal to 0.25 tan
b
times the load specified in paragraph
(c) of this section. The side load must
be applied perpendicularly to the plane
of symmetry at a point midway be-
tween the keel and the chine.
(f)
Immersed float condition. The re-
sultant load must be applied at the
centroid of the cross section of the
float at a point one-third of the dis-
tance from the bow to the step. The
limit load components are as follows:
vertical
aft
side
=
=
⎛
⎝
⎞
⎠
=
⎛
⎝
⎞
⎠
ρ
ρ
ρ
g
x
y
V
C
V
KV
C V
KV
S
S
2
2
2
2
2
3
0
2
3
0
where—
r
= mass density of water (slugs/ft.
2
);
V = volume of float (ft.
2
);
C
x
= coefficient of drag force, equal to 0.133;
C
y
= coefficient of side force, equal to 0.106;
K = 0.8, except that lower values may be used
if it is shown that the floats are incapa-
ble of submerging at a speed of 0.8
V
S0
in
normal operations;
V
S0
= seaplane stalling speed (knots) with
landing flaps extended in the appropriate
position and with no slipstream effect;
and
g = acceleration due to gravity (ft./sec.
2
).
(g)
Float bottom pressures. The float
bottom pressures must be established
under § 25.533, except that the value of
K
2
in the formulae may be taken as 1.0.
The angle of dead rise to be used in de-
termining the float bottom pressures is
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