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National Advisory Committee for Aeronautics, Report - Pressure Distribution Tests on a Series of Clark Y Biplane Cellules with Special Reference to Stability

The pressure distribution data discussed in this report
represent the results of part of an investigation conducted
by the National Advisory Committee for Aeronautics on
the factors afiecting the aerodynamic safety of airplanes.
(l he present tests were made on semispan, circular-tipped
Clark Y airfoil models mounted in the conventional man-
ner on a separation plane. Pressure readings were made
simultaneously at all test orifices at each of 20.angles of
attack between —8° and +90°.
The results of the tests on each wing arrangement are
compared on the bases of maximum normal force coefii—
cient, lateral stability at a low rate of roll, and relative
longitudinal stability. Tabular data are also presented
giving the center of pressure location of each wing.
A review of the general problem of the aerodynamic
safety of airplanes shows that the combination of flight
characteristics peculiar to the conventional airplane
at high angles of attack is one of the most prolific
sourbes of danger—a situation that is directly traceable
to the fact that the greatest and most sudden changes
in lift and stability occur at these attitudes.
To increase the rather meager general information
on airfoils operating in this angular range the National
Advisory Committee for Aeronautics has conducted a
comprehensive investigation of the aerodynamic char-
acteristics of a large series of Clark Y monoplane and
biplane combinations up to 90° angle of attack. This
research consisted of force tests, autorotation tests, and
pressure distribution tests, all made in the 5-foot at-
mospheric wind tunnel of the N-. A. C. A. (reference
1), at a Reynolds Number of about 150,000.
The results of the force tests have been reported in
references 2 and 3, the autorotation tests in reference
4, and the preliminary results of the pressure dis-
tribution tests in references 5, 6, and 7. The present
report is a compilation and analysis of all the pressure
distribution data given in the last three references.
Analysis of the data presented in this report covers
(1) the effect of wing arrangement on maximum normal
force; (2) the effect of wing arrangement on lateral
stability at high angles of attack; and (3) the effect
of wing arrangement on longitudinal stability.