Sec. 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:
where --
L=limit load (lbs.);
C5=0.0053;
VS0=seaplane stalling
speed (knots) with landing flaps extended in the appropriate position and
with no slipstream effect;
W=seaplane design landing weight in pounds;
βS=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
ry=ratio of the lateral distance
between the center of gravity and the plane of symmetry of the float to
the radius of gyration 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 resultant water load consists of a component equal to 0.75 times the
load specified in paragraph (a) of this section and a side component equal
to 3.25 tan β 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 resultant water load consists of a component equal to 0.75 times the
load specified in paragraph (b) of this section and a side component equal
to 0.25 tan β 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 between the keel and the chine.
(f) Immersed float condition. The
resultant load must be applied at the centroid of the cross section of the
float at a point one-third of the distance from the bow to the step. The
limit load components are as follows:
where --
ρ=mass density of water (slugs/ft. 2);
V=volume of float (ft. 2);
Cx=coefficient of drag force, equal
to 0.133;
Cy=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 incapable of submerging at a speed of 0.8
VS0 in normal operations;
VS0=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 K2 in the formulae may be taken as 1.0. The angle of
dead rise to be used in determining the float bottom pressures is set
forth in paragraph (b) of this section.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25-23, 35 FR 5673, Apr. 8, 1970]