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National Advisory Committee for Aeronautics, Technical Notes - Hydrodynamic Characteristics of a Low Drag Planing Tail Flying Boat Hull

The hydrodynamic characteristics of a flying boat incorporating a
low—drag; planing-tail hull were determined from model tests made in
Langley tank no. 2 and compared with tests of the same flying boat
incorporating a conventional type of hull. The planing—tail model had
a greater range of elevator deflection and center-of—gravity location
for stable take-offs than did the conventional model. No upper—limit
porpoising was-encountered by the planing-tail model. The maximum
changes in rise during landings were lower for the planing—tail model
than for the conventional model at most contact trims, an indication of
improved landing stability for the planing-tail model. The hydrodynamic
resistance of the planing-tail hull was lower than that of the conven-
tional hull at all speeds, and the load-resistance ratio was higher for
the planing-tail hull, being especially high at the hump. The static
trim of the planing-tail hull was much higher than that of the conven-
tional hull, but the variation of trim with speed during take-off was
smaller.

In the search for a flying-boat hull that would have low air drag,
a wind—tunnel investigation was made with several models of planing-tail
flying-boat hulls. The results of this inyestigation are given in refer-
ences l and 2 and indicate that a deep-stepped planing-tail hull with a
very full step fairing will have much lower air drag than that of a
comparable conventional type of hull. Resistance tests previously made
with planing-tail hulls (references 3 to 5) indicate that this type of
hull can be expected to have lower hydrodynamic resistance than a com-
parable conyentiOnal hull. A dynamic model was fitted.with a planing-
tail hull, the lines of which closeLy approximated those of the lowest-
drag hull reported in reference 2. The hydrodynamic characteristics of
the model fitted.with the planingatail hull are given in this paper and
are compared with the hydrodynamic characteristiCsfof_the same model
fitted with a conventional type_of hull. The hydrodynamic character-'
istics ofrthese models were determined during tests made in Langley
tank no. 2.using the procedure of reference 6.