Federal Aviation Administration, DOT

Section 25.533

n=

C TO VS12
- tan 23  - W 13
-
-

spaschal on DSK3GDR082PROD with CFR

where - 
n = inertia load factor;
CTO = empirical seaplane operations factor
equal to 0.004;
VS1 = seaplane stalling speed (knots) at the
design takeoff weight with the flaps extended in the appropriate takeoff position;
b = angle of dead rise at the main step (degrees); and

Section 25.533 Hull and main float bottom
pressures.
(a) General. The hull and main float
structure, including frames and bulkheads, 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 distributions must be applied:
(1) For an unflared bottom, the pressure at the chine is 0.75 times the pressure at the keel, and the pressures between the keel and chine vary linearly,
in accordance with figure 3 of appendix
B. The pressure at the keel (psi) is
computed as follows:

Pk = C2 

K 2 VS12

tan  k
where - 
Pk = pressure (p.s.i.) at the keel;
C2 = 0.00213;
K2 = hull station weighing factor, in accordance with figure 2 of appendix B;
VS1 = seaplane stalling speed (Knots) at the
design water takeoff weight with flaps
extended in the appropriate takeoff position; and
bK = 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 linearly, in accordance with figure 3 of appendix B. The pressure distribution is
the same as that prescribed in paragraph (b)(1) of this section for an
unflared bottom except that the pressure at the chine is computed as follows:

Pch = C3 

K 2 VS12
tan 

where - 
Pch = pressure (p.s.i.) at the chine;
C3 = 0.0016;
K2 = hull station weighing factor, in accordance with figure 2 of appendix B;

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EC28SE91.040</MATH>

For the wing and its attachment to
the hull or main float - 
(a) The aerodynamic wing lift is assumed to be zero; and
(b) A downward inertia load, corresponding to a load factor computed
from the following formula, must be
applied:

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-23, 35 FR 5673, Apr. 8,
1970]

EC28SE91.039</MATH>

Section 25.531 Hull and main float takeoff
condition.

W = design water takeoff weight in pounds.

EC28SE91.038</MATH>

(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 direction of the upward component of the
load is the same as that in the symmetrical condition, and the point of application of the side component is at
the same longitudinal station as the
upward component but is directed inward 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 Section 25.527. The
side load is directed inboard, perpendicularly to the plane of symmetry
midway between the keel and chine
lines of the float, at the same longitudinal station as the upward load.