Hydrodynamic-stability tests of a model of a flying boat and of a planing surface having a small downward projection (hook) on the planing bottom near the step Page: 2 of 8

                                
3 1176 01363 9763
r
NATIONAL ADVISORY COMMITTE-ZOR ARONAUTICS
R EBTRIOT3D ULIIT IN
HYDRODYNAIIC-STAILITY TESTS 07 A MODL OF7 A
LYING BOAT AD 07 A PLANING SURFACE HAVING
A SKALL DOWNWARD PROJECTION (BOO0) ON THE-
PLANING BOTTOM NAR TEl STEP
By James K. Benson
SULkARY
Stability tests of two dynamic models in NACOA tank
no. 1 were carried out to investigate briefly the effects
of adding a small projection (hook) on the p laning bottom
of the forebody near the eteu of a seaplane. Tests with
a wedge-shape and a half-round projection extending the
full width of the model and extending downward about
eight-tenths of 1 percent of the beam had rather large
effects upon all trim limits and also upon the landing
stability. All trim limits were lowered, about 40 at
high speeds, and the tendency to skip on landing was in-
creased.
INTRODUCT I ON
The planing bottom of a seaplane of current design
generally has no longitudinal curvature in the forebody
near the step. Tank tests of models (references 1 and 2)
have indicated that some desirable effect upon the resist-
ance and trimming-moment characteristics may be obtained
by use of a small hook at the step.  Service trials of a
flying boat fitted with a hooked step have shown very un-
desirable stability characteristics (see reference 2),
particularly at landing; this effect has caused the Bureau
of Aeronautics to discontinue the use of that form of bot-
tom. During tests of dynamic models in MACA tank no. 1. .
it has been observed occasionally that relatively small
irregularities on the forebody near the step - for example,
wrinkles in the film used to cover the bottom - caused a
noticeable reduction in the lower trim limit of stability.