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National Advisory Committee for Aeronautics, Technical Notes - Hydrodynamic Tests in the NACA Tank of a Model of The Hull of the Short Calcutta Flying Boat

The hydrodynamic characteristics of a model of the
hull of the Short Calcutta (N.A.C.A. Model 47) are pre—
sented in nondimensional form. This model represents one
of a series of hulls of successful foreign and domestic
flying boats the characteristics of which are being ob-
tained under similar test conditions in the N. A. C. A. tank.

The take—off distance and time for a flying b—oat hav~
ing the hull of the Calcutta are compared at two values of
the gross load with the corresponding distances and times
for the same flying boat having hulls of two representa—
tive American types, the Sikorsky 5—40 and the N.A.C.A.
ll—A. This comparison indicates that for hulls of the
widely different forms compared, the differences in take—
off time and distance are negligible.

The N.A.C.A. is testing a series of models represent—
ing the hulls of various successful foreign and domestic
flying boats. The chief puryose of these tests, as point—
ed out in reference 1, is to obtain directly comparable
hydrodynamic characteristics of the hulls. The knowledge
thus obtained should result in a concentration of future
development on the forms showing the greatest promise.
While it is realized that hulls of the different types
used by the designers in different countries require dif—
ferent technique in handling while on the water, compara—
tive data as to the hydrodynamic charaCteristics should be
of considerable value to all designers.

The present tests were made of a model of a hull rep~
resenting that of the Short Calcutta, a successful British
Short Bros., Ltd. The hull of—the Calcutta has a trans- ‘
verse second step, a forebody of approximately half the
length to the second step, and an ex-tended beam at the
chines. The grOss load and take-off speed, as stated by
the d.esigners, are 21, 700 pounds and 51— 1/2 knots, respec—
tively.

The model as tested in the N.A.C.A. tank (N.A.C.A.
Model 4?) was constructed to a scale of 17:119.90, or ap-
proximately 1/7, and was of laminated mahogany, painted
and rubbed, with a tolerance on the offsets of j=O.OE inch.
The model was constructed with fair deck and sides, fol-
lowing the design of the actual Calcutta hull, for the
purpose of obtaining the aerodynamic characteristics from
wind—tunnel tests in_another investigation. The principal
lines are shown in fligure 1 and the offsets are given in
tablerl. Figure 2 shows the mo del as tested in the tank.