• Version
• 133 Downloads
• 921.11 KB File Size
• 1 File Count
• August 30, 2016 Create Date
• August 30, 2016 Last Updated

National Advisory Committee for Aeronautics, Report - The Additional Mass Effect of Plates as Determined by Experiments

The apparent increase in the inertia properties of a
body moving in a fluid medium has been called the
additional-mass eject. This report presents a résumé of
test procedures and results of experimental determinations
of the additional-mass efiect Qfflat plates. In addition
to data obtained from carious foreign sources and from
an NACA investigation in 1938, the results of tests'
recently conducted by the National Advisory Committee
for Aeronautics are included. In the recent NAC’A
tests, the additional—mass effect of rectangular plates of
varying aspect ratio was redetermined, and the additional-
mass eject of plates having tapered plan forms was
investigated for the first time.

A test procedure is described by means of which values
of additional mass are obtainedr as the diference between
the moments of inertia of the plates experimentally de-
termined in air and in vacuum.

The results of the present NACA tests, believed to be
more accurate than data obtained in the older investiga-
tions, fall a little above the data obtained by the NAC‘A in
1933 and somewhat below the values published in Germany
in 1937’. The German values appear erroneously high
on the basis of theoretical considerations.

That the mass of a moving body is apparently greater
in a fluid medium than in a vacuum was noted as early
as 1836 (reference 1). The apparent increase in mass
can be attributed to the additional energy required to
establish the field of flow about the moving body.
Inasmuch as the motion of the body may be defined
by considering its mass as equal to the actual mass of
the body plus a fictitious mass, the effect of the inertia
forces of the fluid may be represented as an apparent
additional mass; this additional mass, in turn, may be
considered as the product of an imaginary volume and
the density of the fluid. The efl’ect of the surrounding
fluid has accordingly been called the additional-mass
efiect. The magnitude of this efl'ect depends on the
density of the fluid and the size and the shape of the
body normal to the direction of motion.