Investigations on the Downwash Behind a Tapered Wing With Fuselage and Propeller Page: 17 of 52
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N.A.C.A. Technical Memorandum No. 876
if S is the drag difference of the reference polar and
of the polar with X =-0.2. The lift coefficient is ca =
0.915. (The ca values in text and diagrams refer to
"wing alone" at the same a.)
Taking the "reference measurements", "wing alone", and
"wing with fuselage" by themselves, it is seen that the
ideal fuselage has caused only on the lateral axis at proes-
suro-side height ch = -0.1 a perceptible disturbance in
downwash of "wing alone" while in the middle at this very
height the fuselage produces no change in downwash.
The reason for the little influence of the ideal fu-
selage is that the lift distribution at a = 3.15 has
been very little affected by the added fuselage.
The effect of propeller running is best presented by
the lateral axis measurement at height Eh = 0.0. The slip-
stream twist in the downwash is plainly noticeable. The
differences due to the twist are of about the same magni-
tude of 40.. The same is approximately true for the lat-
eral axis curve at height Eh =-0.1, if it is assumed that
the slipstream has removed the hole in the downwash distri-
bution of the reference measurement "wing with fuselage"
of this lateral axis (dashed part of the curve). On con-
necting (fig. 24) the centers of the zones of maximum and
minimum downwash, the connecting line meets the plane of
symmetry of the model about in point Eh = -0.03. This
point should coincide with the slipstream center because
there is scarcely a lateral movement of slipstream (cf.
From the accord of the aw points of the "reference
model" and of the "model with propeller running" at q = 0
(fig. 23) it may further be inferred that. the slipstream
center line at a = 3.150 and X = 0.2 adapts itself to
the flow prescribed by the model without propeller. It is
therefore neither sideways, upward,nor downward deflected.
The answer to the question of validity for any other A
values or propeller loads is found in figure 25. According
to it an increasing r.p.m. is followed by a slight lateral
slipstream deflection to the left and - conformably to the
rising circulation - downward. The opposite tendency is
shown by the slipstream if the propeller windmills.
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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/m1/17/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.