Flight tests of an airplane showing dependence of the maximum lift coefficient on the test conditions Page: 2 of 16
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3 1176 01433 6995
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
TECHNICAL NOTE NO. 622
FLIGHT TESTS OF AN AIRPLANE SHOWING DEPENDENCE OF THE
MAXIMUM LIFT COEFFICIENT ON THE TEST CONDITIONS
By H. A. Souls and James A. Hootman
Data are presented to show the extent to which the
maximum lift coefficient and, consequently, the minimum
speed of an airplane, as determined by flight tests, may
vary xith test conditions. The data show that 0L may
vary by as much as 14 percent, depending on the altitude
and wing loading at which the tests are made, the position
or motion of the propeller, and the rate at which the an-
gle of attack is changing when the maximum lift coeffi-
cient is obtained. The variation of the maximum lift co-
efficient with these factors, which are under the control
of the test engineer, shows the need of standardizing the
test procedure. A further variation is shown with wing
conditions as affected by weathering and vibration, fac-
tors that cannot be completely controlled.
General experience with the measurement of minimum
speeds and maximum lift coefficients has indicated con-
siderable difficulty in obtaining agreement between suc-
cessive measurements on a given airplane, between wind-
tunnel and flight tests of a complete airplane, and be-
tween measured and predicted minimum speeds for a given
airplane. The purpose of the present paper is to present
N.A.C.A. flight experience with one airplane and to dis-
cuss the factors that were found to affect the minimum
speeds and the maximum lift coefficients obtained under
different test conditions. The factors investigated wore
Reynolds Number, which was varied by changing the wing
loading and altitude, propeller condition, rate of change
of angle of attack, and wing-surface condition. The data
were obtained in connection with one phase of a general
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Soule, H A & Hootman, James A. Flight tests of an airplane showing dependence of the maximum lift coefficient on the test conditions, report, November 1, 1937; (digital.library.unt.edu/ark:/67531/metadc54381/m1/2/: accessed March 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.