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National Advisory Committee for Aeronautics, Technical Notes - The Calculation of Wing Float Displacement in Single Float Seaplanes

The lateral stability of all single-float seaplanes and
flying boats except those of the Dornier type with lateral ex—
tensions on the hull itself must be assured by the use of auxil—
iary floats at the wing tips, these floats being mounted high
enough so that they make contact with the water only when the
seaplane is heeled over to one side or the other and so that one
ly one of the wing floats can be in contact with the water at a_
given time.

In calculating the proper size for such wing floats, the
stability of the main central float is often entirely neglected,
the position of center of buoyancy being assufied independent of
the angle of inclination. The weight carried by one of the auxs
iliary floats in still water and still air can then be CfilCUr
lated directly by taking moments around the center of buoyancy
with the machine in the inclined position, and the total volume
which the wing floats should have can be calculated if it is as~
sumed that a fixed reserve of buoyancy is desirable there, just
as it is for the main float. It is then necessary only to mul—
tiply the weight carried by the wing float under ideal conditions
by a fixed constant to find the desirable total displacement.
The application of this method has been explained in detail with
calculations for a number of specific examples, in a recent pub—
lication (Reference 1).

The use of a fixed reserve of buoyancy has several possible
disadvantages in certain special cases. In the first place; it
is liable to lead to incorrect results for machines with a very
low center of gravity, such as flying floats. The instability
of the main float alone is small in such cases, and even a 100
percent reserve may represent a very small absolute addition to
the size of the wing float. It will be observed that the re~
serve buoyancy of the wing floats is exceptionally large on most
flying boats which have proven satisfactory in actual service.
On the NC, for example, the reserve was 490 percent. A method
which would give a constant independent of size and height of
C.g. would obviously be desirable. Second, and by similar rea—
soning, the use of a constant reserve of buoyancy takes no ac—
count of the stability of the main float.