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National Advisory Committee for Aeronautics, Technical Notes - A Study of Water Pressure Distributions During Landings with Special Reference to a Prismatic Model Having a Heavy Beam Loading and a 30° Angle of Dead Rise

A landing investigation is being conducted at the Langley impact
basin to obtain some quantitative measurements of the distribution of
water pressure during landings, which may serve as an aid in the estab—
lishment of seaplane design criteria and in determining the value of
the existing hydrodynamic pressure theories. This paper presents pres—
sure measurements obtained on a 5—foot prismatic model having an angle
of dead rise of 30°, a beam of 1 foot, and a beamrloading coefficient
of 18.8. This model was subjected to smooth—water landings at fixed
trims of 6°, 15:, 30°, and 15° for a range of flight—path angles from
approximately 2 to 20°.

Initial impact conditions and maximum.pressures are presented for
all landings together with time histories of the velocities and pressure
distributions for several representative landings. The instantaneous
pressures for a given draft, trim, and location on the hull bottom are
found to be directly proportional to the square of the velocity normal
to the keel.

Comparisons of the experimental pressures and theoretical pressures
indicate the-degree of correlation and some limitations of the available
theoretical-treatments.

Inasmuch as the magnitude and distribution of the hydrodynamic
loads imposed on seaplane hulls during landings is a matter of concern
to seaplane designers, an appreciable amount of research has been con—
ducted to obtain reliable means of predicting these loads. In recent
years much of this research has been concerned with the overhell loads
problem, for some phases of which theories haVe been developed and sub-
sequently substantiated by experimental investigations. In general,
however, a knowledge of the over—all loads is not a sufficient criterion
for local structural design since, during seaplane landings, large and
irregular pressure gradients usually exist over the hull bottom such that
the local pressures greatly exceed the average pressures.