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Wind Tunnel Investigation of Control Surface Characteristics - II - A Large Aerodynamic Balance of Various Nose Shapes with a 30% Chord Flap on an NACA 0009 Airfoil

SUMMARY

Tests have been made of an NACA 0009 airfoil with a
30~percent~chord flap having a 49.5—percent flap-chord
balance with various nose shapes and tro gaps. The re-
sults have been presented in the form of aerodynamic sec—
tion characteristics.

Tnese results indicated the flap to be overhalanced
when deflected, regardless of nose shape. There was only
a slight change in hinge moment with angle of attack. A
blunt—nose shape gave the greatest reductions in hinge
moment and/the smallest increment of drag over that of a
plain airfoil. The small gap investigated affected the
aerodynamic characteristics only slightly.

A method has been proposed for reducing the control
forces to any desired value While, at the same time, mark-
edly increasing the lift effectiveness of the airfoil—flap
combination over that of a plain flap of the same chord.
In addition, the flap can be made to float against the
relative wind thereby causing the stability with controls
free to exceed that with controls fixed. These results
are accomplished by using a differentially operated bal-
ancing tab on an overbalanced flap to increase both the
lift and the hinge moment of the flap.

IHTBODUGTION

Because of the increasing size and speed of modern
airplanes, it has become increasingly necessary to reduce
the hinge moments on the control surfaces and thus to
:4

reduce the forces on the control stick. In an effort to
solve this problem, the NACA has initiated an extensive
investigation of the aerodynamic characteristics of con-
trol surfaces in order to provide data for design purposes
and to determine the type of flap arrangement best suited
for use as a control surface. Because a conventional con-
trol surface is merely a flap on an airfoil, these two
terms are used synonymously.

As a part of this investigation, some effects of flap
nose shape and gaps on a typical horizontal tail of finite
Span were determined in the full—scale wind tunnel and are
reported in reference 1. The more fundamental part of the
investigation, however, is being made in two—dimensional
flow. The first part of the two~dimensional flow investi—
gation was the determination of the section characteris~
tics of airfoil—flap combinations using plain flaps of
various sizes and with sealed gaps. (See references 2, 3,
and 4.) The data presented in these references have been
analysed, and parameters for determining the characteris-
tice of a thin symmetrical airfoil with a plain flap of
any size chord and with the gap at the flap nose sealed
are given in reference 5. The effects of gap size on the
characteristics of a thin airfoil with a plain flap are
reported in reference 6.

The tests reported herein were made to provide sec-
tion data for an airfoil having a flap with a large over—
hang and to determine the effects of the shape of the
nose of this overhang. The terms "balance" and "overhang"
are used synonymously to indicate the portion of the mov—
able surface ahead of the hinge axis.