• Version
• 98 Downloads
• 278.57 KB File Size
• 1 File Count
• November 4, 2016 Create Date
• November 4, 2016 Last Updated

National Advisory Committee for Aeronautics, Technical Notes - The Reaction on a Float Bottom When Making Contact with Water at High Speeds

As an explanation of the observed phenomenon, I would
suspect an initial suction which, combined with down ele—
vator, starts rotation and throws the bow deep. The suddenly
increased displacement combined with the lift on the elevators
then supplies the lift for the "bounce" before the rotation
loan be checked. This analysis is borne out by Model Basin
tests made at the Washington Navy Yard, and given in the Appen—
dix. These tests were made to investigate the possibility of
a serious accident arising from unintentional contact with the
water in substantially horizontal flight at high speed. Re—
ferring to the vector diagrams on Figure 8, it will be seen
that a very dangerous condition may arise if the float be al~
lowed to come in contact with the water at high speeds as,.
for example, when flying at high speed just above the surface
of the water. The initial diving moment due to suction and
drag combined may be great enough to cause the seaplane to
nose under before the pilot is able to control the motion.

The same test data indicate clearly the existence of forces
and moments tending to produce the phenomenon observed by Mr.
Carroll, when the maneuver is carried out at lower speeds, as
in a landing. The first effect of reducing the trim to about
00 by the stern in a landing is to set up a fairly large div—
ing moment due to suction and resistance. The bow of the
float then dips down, the displacement is suddenly increased
and the resultant force is directed upward, throwing the sea—
plane olear. All of this will happen very quickly so that it
is quite probable that the rotation will be unchecked.
I would like to emphasize the fact that it may be very
dangerous to fly at low angles of attack and high speeds just
above the surface of the water. In this position an accidental
contact with the surface of the water may lead to a serious
crash.

Purpose of test.— The purpose of the experiments was
to determine the direction and approximate value of the water
reaction on the bottom of a float forward of the step, when
making contact with the water at high speed, and trimmed by
the bow.