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National Advisory Committee for Aeronautics, Technical Notes - Analysis of Planing Data for Use in Predicting Hydrodynamic Impact Loads

An analysis is made of planing data covering a wide range of dead—
rise angles, trims, speeds, and beam loadings. General hydrodynamic—
impact—load equations are applied to the planing float and corrections
are made to the‘theoretical nondimensional coefficients which are used in
defining the effect of the apparent additional mass associated with the
immersed body in order to obtain agreement with experimental planing
data. The analysis is divided into three phases in which the inertia
force is determined by evaluating data from tests in which the chines
are above level water and the buoyant force is negligible, data from tests
in which the chines are above level water and the buoyant force is signifi—
cant, and data from tests in which the chines are immersed with buoyant
and steady-flow forces included.

The results of the analysis include equations for the inertia force
which contain correction factors to compensate for the effect of gravity
upon the growth of the apparent additional mass at low Froude numbers.
Summary equations for the total water reaction are obtained from the
three phases of the analysis and are found to give excellent agreement
with experimental planing data for dead—rise angles between 10° and 11-00.

The planing coefficients and gravity correction factors which are included
in the resultant equations may be substituted directly in the general
hydrodynamic—impact—load equations for angles of dead rise between 10° and 30°
if the buoyant and steady—flow forces, considered in the analysis of planing
data, are also used and if the effect of gravity at different Froude
numbers, indicated by the analysis of planing data, is assumed to be
unaffected by the accelerations which occur during impact.

The magnitude of hydrodynamic loads experienced by seaplanes during
a landing impact has been investigated experimentally and theoretically
by the National Advisory Committee for Aeronautics. The results as
reported in references 1 and 2 provide a rational means of determining
loads on conventional V—bottom hulls in a step landing.