Note on the Air Forces on a Wing Caused by Pitching. Page: 3 of 7
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N.A.C.A. Technical Note No. 217
introduce certain simplifying assumptions in order to obtain at
least the main portion of the forces produced. This approximate
or theoretical solution should be compared with the results of
careful measurements of the same quantity. The comparison would
constitute the right interpretation of such tests. The differ-
ences between the test results and the computed results would
throw light on the general physical qucstions involved in the spe-
cial problem in question. Its theme is the unsteady motion of
fluids, more especially of air.
*The research work of the past has been chiefly confined to
the investigation of steady motion only. Unsteady motion is of
equally great practical importance to aeronautical technics, and
its study should be taken up exhaustively. Let us begin by deter-
mining the air force on a wing which is in the process of chang-.
ing its angle of attack at a finite rate of pitching angular veloc-
The simplified treatment to which I have to take recourse for
want of proper empirical information, is based on the assumptions
used with success and with better justification for wings in a
steady translatory motion. This is Kutta's condition. Kutta as-
sumes that each wing of infinite span gives rise to that poten-
tial flow that closes itself at the point of the sharp rear edge,
rather than to any other potential flow that gives rise to infi-
nite velocities in the neighborhood of the rear edge. This condi-
tion is plausible for steady motions and leads to a good agreement
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Munk, Max M. Note on the Air Forces on a Wing Caused by Pitching., report, March 1925; (https://digital.library.unt.edu/ark:/67531/metadc53912/m1/3/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.