Investigations on the Downwash Behind a Tapered Wing With Fuselage and Propeller Page: 9 of 52
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8 N.A.C.A. Technical Memorandum No. 876
Thus the measurement was not extended very much into
the climbing range (high propeller loading). Nevertheless,
it will be seen that extrapolation affords some safe pre-
dictions concerning the climbing range (figs. 48, 49, 64,
and 65). For the time being the principal aim was to cre-
ate a general picture of the flow phenomena around the tail
with propeller running and different fuselage forms. This
also explains our preference for the point-by-point measure-
ment with the dual tube instrument which at the same time
allows accurate averaging. It was also the reason for the
searching velocity distribution measurement - although only
on the low-wing model with angular fuselage and only at one
angle of attack and one coefficient of advance in vicinity
of the tail (c. = 1.0).
The downwash measurements were largely effected in a
transverse plane at E = 1.0 distance from the wing, ex-
tending over three to six lateral axes and three vertical
axes. On the low-wing models they were supplemented by
measurements on two horizontal axes above or below the fu-
selage in the plane of symmetry of the model and to the
right and left of the fuselage at height Eh = 0, although
the measurements did not include different r.p.m. for all
axes. Individual reference measurements, moreover, must be
obtained by interpolation. On the "wing alone" it further
include the longitudinal axis at wing height and in the
plane of symmetry.
2. Aspect of Downwash. Curves
a. Wing Alone
Vertical axes.- Figure 6 shows for a = 6.80 the
nondimensional angles of downwash on a vertical axis at
distance a = 1.0 and approximately in the plane of sym-
metry of the wing at C q = 0.12.. These values may be
equated to those of the plane of symmetry, because the
downwash figures do not change within a certain range in
the transverse direction. xcept for the peak, the curve
resembles that of the rectangular and elliptical wing (ref-
erence 1) (fig. 18). A wide range of maximum values is
distinctly noticeable in the pressure side flow, i.e., at
negative th values, but not however - as would be expect-
ed on the basis of the calculation with a simple trailing
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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/m1/9/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.