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National Advisory Committee for Aeronautics, Technical Notes - Wind Tunnel Pressure Distribution Tests on an Airfoil with Trailing Edge Flap

This report deals with pressure distribution tests on an
airfoil with a conventional trailing edge flap. These tests
were conducted in the Atmospheric Wind Tunnel of the National
Advisory Committee for Aeronautics.

Maximum chord loadings were obtained with the flap displaced
downward and with the airfoil at large angles of attack. Great—
er changes were produced in the normal force and in the center
of pressure travel by up—flap than by an equal down—flap dis—
placement.

This investigation was conducted for the purpose of obtain—
ing information on the distribution of pressure for two—dimen—
sional flow over an airfoil equipped with a plain trailing edge
flap. The tests were made in the FiveeFoot Atmospheric Wind
Tunnel (Reference 1) of the Langley Memorial Aeronautical Labor—
atory.

When a trailing edge flap is displaced from its neutral po—
sition, the magnitude and distribution of pressure over both
airfoil and flap are changed. The property of increasing or de—
creasing lift has resulted in the common use of flaps as ailer—
ons for controlling the attitude, and hence the motion of an
airplane in flight. Flaps are also used to a limited extent to
obtain lower landing speeds by increasing the maximum lift coef—
ficient of the wing.

To use flaps as control surfaces, it is desirable to know
how much control can be obtained by displacing them and also
the force required to operate them. For a flap used on a wing
to decrease landing speed, in addition to the above information,
it is necessary to know how flap displacement affects the bal—
ance or "trim“ of the airplane.

The foregoing factors can be determined by a study of the
normal force characteristics, center of pressUre movement, and
the moments of the air loads on the flap about the hinge. The
results of numerous force tests have already been published,
but relatively little information is available from pressure
distribution tests. The pressure distribution tests described
in this report are a part of a preliminary test program which
has been carried out at this laboratory on several different
types of flaps