• Version
• 215 Downloads
• 1.50 MB File Size
• 1 File Count
• August 31, 2016 Create Date
• August 31, 2016 Last Updated

National Advisory Committee for Aeronautics, Report - A Theoretical Investigation of Hydrodynamic Impact Loads on Scalloped Bottom Seaplanes and Comparisons with Experiment

An analytical method is presented for calculating the hydro-
dynamic impact loads and motions experienced by seaplane
floats and hulls with scalloped (fluted) bottoms. The analysis
treats cortical impact at zero trim in addition to the more general
problem of the step impact of a seaplane at positire trim where
the flight path. is oblique to the heel and to the water surface.
Also considered are the transformations required to represent
impacts into u‘a res.

The analysis, which is equally applicable to floats hating
cross sections of any shape, considers that the flow about an
immersing planing bottom occurs largely in transverse flow
planes which are normal to the lceel. The equations of motion.
are written in general terms and require the determination of
the cirtual water mass as afunction of the depth of penetration
of the heel into the flow planes. 0n the basis of a simple
extension of ll’agner’s expanding-plate analogy, equations are
presented whereby the section characteristics, "which determine
the virtual mass, may be calculated for any giren float shape.

In order to illustrate the applicability of the analysis to
practical problems, time histories of the applied hydrodynamic
load have been calculated for specific impact conditions and are
compared with Langley impact—basin test data obtained in
smooth and rough water with a double—scalloped—bottom sea—
plane float which is representatire of current commercial and
xerinlce types.

Investigations conducted by the National Advisory
Committee for Aeronautics during the past several years
have indicated that. current seaplane design specifications
are inadequate and that more rational means are required
for predicting hydrodynamic loads. In order to provide
further information on the problem of impact loads, an
analytical and experimental research program is now in
progress at the Langley impact. basin, the theoretical phase
of which has resulted in the investigations presented in
references 1 and 2, which deal primarily with V-bottom
floats.