Investigations on the Downwash Behind a Tapered Wing With Fuselage and Propeller Page: 10 of 52
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vortex (reference. 1)* - at approximately wing height and
the drop of the downwash values toward both sides of the
peak -is,- ontrarr- to- the theoretical- curve for the simple
trailing vortex, unsymmetrical and greater, The peak of
.the curve in figure 6 lies (dual-tube record) in vicinity
of the stagnation point streamline as shown by a relative
evaluation of the normal axis curves of the earlier meas-
ured elliptical wing (reference 1), which at the same time
included a measurement of the position of the rear stagna-
tion point streamline.
To establish the effect of finite wing chord on the
downwash curves of the vertical axis (the same used in the
earlier tests) (reference 1) the streamline pattern for air-
foil No. 387 in two-dimensional flw was lotted according
to the Karman-Treffts method (reference 6), The lift co-
efficient was ca = 1.156, corresponding to the circulation
at wing center with a mean ca value of ca = 1.0 for a
rectangular wing of 1:5 aspect ratio. The angles of down-
wash were taken from the streamline pattern. We also com-
puted these for the same circulation
r = ca t
for the case of the lifting line. Referring the th and
LE values to a fictitious span of b = 5 t the expression
h + - (he + a )
The result is shown in figure 15, whore the angles of
downwash for finite wing chord and the "lifting line" are
plotted against Ch. The curves for the former are not as
flat as those for the "lifting line" and drop a symetrical-
ly. They therefore resemble the experimental curves better
*The formula on page 32 of reference 1 omits the factor 0.5
in the second term of the denominator, which conditions ver-
tical axis asymmetry, But it does not affect th.e result,
N.A.C.A. Technical Memorandum No. 876
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Muttray, H. Investigations on the Downwash Behind a Tapered Wing With Fuselage and Propeller, report, September 1938; (https://digital.library.unt.edu/ark:/67531/metadc63295/m1/10/: accessed April 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.