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*

*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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