Investigations on the Downwash Behind a Tapered Wing With Fuselage and Propeller Page: 19 of 52
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N.A.C.A. Technical Memorandum No. 876
On comparing figure 28 with figure 29 it will be found
that the curves, both the reference curves and those taken
with propeller running are remarkably alike for the same
height position, with exception of 6h = -0.2, for which
the statement scarcely holds.
The latter might be associated with the fact that the
height of ch = -0.2 at distance ( = 1.0 is exactly the
height of the free vortex sheet (figs. 30 and 31; also fig.
6). The reference curve of owing with fuselage" at height
ch = -0.2 in figure 29 indicates jags within cq = -0.25
to +0.25, which probably are traceable to a nonuniform
lift distribution over the wing roots or to the lateral
keels of the fuselage-wing fillets. On this unstable curve
the downwash changes, due to the slipstream effect, are
built up. The last cited changes resemble those of the
corresponding lateral axis curve at a = 3.150, although at
a = 3.150 the lateral axis for Ch = -0.2 already lies
below the free. vortex sheet.
The similarity of the downwash curves of figures 23
and 29 is further restriced by the fact that at increasing
a the slipstream becomes smaller, as exemplified especially
by the lateral axis curves for ch = 0 in figures 23 and 29.
The reduction was at the expense of the right half of the
superposition due to the twist. Figure 32 (lateral axis
curves at a = 10.60) manifests the same phenomenon. It is
probably associated with the increasing yaw of the propeller
as a is raised. With approximately horizontal propeller
setting the right-side blade angle is smaller than that of
the left-side blade, as a result of which the centroidal
thrust distribution shifts toward the left (cf. fig. 25).
The downwash curves for the vertical axis in figures30
and 31 do not confirm the statement made for a = 3.150o,
namely, that the slipstream effect on the pressure side is
still traceable at great distance away from the wing. Now
it rather applies to the suction side, especially to the
right half of the wing outside of the slipstream.
= 10.,6.- The lateral axis curves of figure 32 ( =
10.60, ca = 1.411, A = 0.1655, ce = 0.642) again dis-
close a certain resemblance - as already indicated - with
the corresponding curves at a = 3.150 and a = 6.80, al-
though accompanied now by stronger deformations, in accord-
ance with the approach to cmax and the pronounced yaw
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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/m1/19/: accessed April 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.