Investigations on the Downwash Behind a Tapered Wing With Fuselage and Propeller Page: 7 of 52
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N.A.C.A. Technical Memorandum.No. 876
The first downwash measurements behind the models
without propeller running were made with small silk threads
because the dual tube downwash recorder used in the earlier
studios (reference 1) was not available, though it did ar-
rive in time for the tests on models with propeller running.
To afford a better comparison of the test data "with" an
"without propeller running," a great portion of the down-
wash measurements behind the models "without propeller run-
ning" were repeated with the dual tube downwash recorder.*
At this place only a very few of the comparative curves
plotted by the two methods will be shown, while for the
rest the more exact results achieved with the dual tube in-
strument will be given.
Figure 5 illustrates - nondimensionally - for "wing
alone" the results obtained on three lateral axes at dis-
tance Ct-= 1.0 from the wing. The agreement is, in general,
good, except for the lateral axis in the pressure-side posi-
tion Eh =-0,2, where greater discrepancies exist.
The cause of this is that this lateral axis lies exactly
at the height of the maximum downwash values, as seen from
figure 6. It includes, for instance, the comparison between
thread measurement and dual tube record for a vertical axis
located at distanco e = 1.0 for c = 0.12. It is seen
that the points of the thread measurements in proximity of
the maximum values were figured as one-sided scattering
points, resulting in the lashed curve. (The peak in the
vertical-axis curves was not expected after the results of
the earlier measurements on the elliptical and rectangular
wing (reference 1). (Cf. fig. 15.)) The air speed for these
downwash measurements was v = 21.0 m/e.
I. FORCE MEASUREMENTS
The results of the force measurements are shown non-
dimensionally in figures 7 to 9 for the "low wing with ideal
fuselage" and in figures 10 to 12 for "low wing with angular
fuselage" plotted against the reciprocal value of the coef-
ficient of advance - = -. The graphs for ca and cw
*Some special experiences gained with this instrument are
to be published in "Luftfahrtforschung."
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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/m1/7/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.