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*

*S*0

= 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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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*

*S*1

= 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*

*S*1

= 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*

*S*1

= 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*

*S*0

= seaplane stalling speed (Knots) with

landing flaps extended in the appropriate

position and with no slipstream effect;

and

*V*

*S*0

= 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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