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National Advisory Committee for Aeronautics, Technical Notes - Effect of Hull Length Ratio on the Hydrodynamic Characteristics of Flying Boats in Waves

An investigation was made of the take—off and landing behavior
in waves of models of a hypothetical flying boat having hull length—
beam ratios of 6 and 15. The flying boat had a design gross weight
of 75,000 pounds, a wing loading of 1+1.1 pounds per square foot, and
a power loading of 11.5 pounds per brake horsepower for take—off.
The hull of high length—beam ratio was designed to meet advanced
requirements for increased speed and increased range for flying—boat
designs and has been shown to have low drag.

An increase in length—beam ratio from 6 to 15, reduced the,
maximum vertical accelerations during landing approximately 25 percent,
increased the maximum angular accelerations during landing 15 to 30
percent, and reduced the motions in trim and rise as Well as the
maximum trim and rise. The reductions in trim and rise would make
landings in waves less hazardous with the hull of high length—beam
ratio than with the hull of low length—beam ratio.

In waves 2 feet high and 110 feet long, the range of speed and
load over which spray entered the propellers during take—off was con—
siderably greater with the length—beam ratio of 15 than with the length—
beam ratio of 6. The spray entering the propellers of the hull with the
high length—beam ratio, however, was acceptable. .The hull with high
length—beam ratio was less likely to reach a dangerous attitude during
take—off than was the hull with low length—beam ratio; the take—off
behavior with the high length—beam ratio was generally less violent.

As part of a general investigation of the effect of hull length—
beam ratio on the aerodynamic and hydrodynamic characteristics of flying
boats, the landing and take—off behavior in oncoming waves of a hypo—
thetical flying boat having'hull length-beam ratios of 6 and 15 have been
determined. These hulls are two of a related series with different length—
beam ratios designed to have similar resistance and spray characteristics
for the same gross Weight and to be physically interchangeable on the
same hypothetical seaplane design. All the hulls have the same lengthe—
beam product and, therefore, become longer and narrower as the length—
beam ratio is increased.