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National Advisory Committee for Aeronautics, Technical Notes - The Aerodynamic Characteristics of Six Commonly Used Airfoils Over a Large Range of Positive and Negative Angles of Attack

A comparatively small amount'of information is avail#
able on the aerodynamic characteristics of airfoils through”
the negative angle-oféattack’range. The available data are
from tests on only a few airfoils at low values of the
Reynolds Number. n

In order to obtain data on the strength-of airplanes in
the inverted flight condition, the Bureau of Aeronautics,
Navy Department. requested that tests be made in the vari—
able density wind tunnel of eixg’commonly used airfoils (the '1
3. the CYH, the 'N 92, the. 0:72 the Boeing 108, and the
G ttingen 398) at negative .an les of attack. In accord—
ance with this request, routine measurements' -of lift, drag;
and pitching moment were made on these airfoils through_the _wn_
2 H.—A.C.A. Technical Note NP: 397

negative angle—ofuattack range. The tests were made at a
value of the Reynolds Number which corresponds to the flight
condition of most airplanes near their landing speeds.

To make the data complete; the results Of hitherto un—
published tests of the same airfoils at pesitive angles of
attack are included in this paper. It presents the results
of the first of two series of tests being made by the Na—
tional Advisory 00mmittee.for Aeronautics to determine the
aerodynamic characteristics of airfoils at negative angles
of attack. A second paper will be published after tests
on several other commonly used airfOils are completed.

Apparatus and Method

A brief description of the redesigned variable densitj'
wind tunnel and its method of Operation will be found_in
reference 11 The customary 5‘by SO'inch polished, rectan—
gulan, duralumin airfoils were used in the tests. The
specified ordinates of the airfoils are given in Table I.

For tests at positive angles of attack airfoils are
mounted on the supporting struts of the balance with the _
sting and struts attached.0n the flat side. For the'tests.'
at negative angles of attack. however, the airfoils were
.inverted and the sting was placed on the curved surface!
so that the flat side, which was then the suction side,
was free from obstructions which might have affected the
value of the maximum lift coefficient