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National Advisory Committee for Aeronautics, Technical Notes - Aerodynamic Characteristics of Three Deep Step Planing Tail Flying Boat Hulls and a Transverse Step Hull with Extended Afterbody

An investigation was made to determine the aerodynamic characteris-
tics in the presence of a wing of three deep-step planing-tail flying-
boat hulls which differed only in the amount of step fairing. The hulls
were derived by increasing the unfaired-step depth of a planing-tail
hull of a previous aerodynamic investigation to a depth of about 92 per-
cent of the hull beam. For the purpose of comparison, tests were also
made of a transverse- -step hull with an extended afterbody.

The investigation indicated that the transverse-step hull with
extended afterbody had about the same minimum drag coefficient, 0.0066,
as a conventional hull and an angle-of—attack range for minimum drag of
3° to 5°. The hull with a deep unfaired step had a minimum drag coef-
ficient of 0.0057; which was 1h percent less than the transverse-step
hull with extended afterbody; the hulls with step fairing had up to
Mk percent less minimum drag coefficient than the transverse—step hull.
Longitudinal and lateral instability varied little with step fairing
and was about the same as for a conventional hull.

In view of the requirements for increased range and speed in_
flying—boat designs, an investigation of the aerodynamic characteristics
of flying-boat hulls as affected by hull dimensions and hull shape has
been conducted at the Langley Aeronautical EEboratory of the National
Advisory Committee for Aeronautics. The results of one phase of the
investigation, presented in reference.l, have indicated that substantial
drag reductions can be obtained for planing—tail flying-boat hulls if
proper step fairings are incorporated in the_hull.' In the present—‘-
investigation, exploratory tests were made to determine whether further
drag reductions might be obtained on this type of hull by deepening the
step and thereby reducing the skin area.

Results of tests in the Langley tank no. 2 (reference 2) have
indicated'that the three deep-step hulls of the present investigation" “
would have satisfactory hydrodynamic characteristics.