Investigations on the Downwash Behind a Tapered Wing With Fuselage and Propeller Page: 3 of 52


2 N,A.C.A. Technical Memoradum No. 876
The downwash distribution over a'lateral axis approxi-
mately in tail vicinity - the, same holds for the velocity
distribution in the slipstream also - becomes very unsym-
metrical with increasing angle of attack as a result of the
yaw of the propeller.
The magnitude of supplementary angle of downwash aver-
aged over a span of 0.3 of that of the wing, with propel-
ler running (compared to model without it) amounts at the
most (at maximum angle of attack and maximum propeller
loading) to no more than about 1.50 at wing level. For
fixed angle of attack the angle of additional downwash
grows linearly with the propeller loading. It is greater
on .the low-wing model with anglular fuselage than on that
with ideal fuselage. It is - like the mean angle of down-
wash of the low-wing models without propeller - materially
influenced by the height level of the tail.
In a stability comparison of both models at equal full
throttle polar, the model with angular fuselage is superior,
the consideration concerning an airplane of conventional
design, that is, in our case, with body-fixed horizontal
tail surface. Again thi.s is primarily associated with the
dissimilar course of the mean angle of downwash on the
height level of the tail.
With assumedly wind-fixed horizontal tail surface,
i.e., constant levol c at increasing a, the stability
increases enormously. I further increase may be looked for
if, with changing a, not only the tail but the "fuselage
with slipstream" as well remain wind-fixed (say by changing
the wing incidence relative to the fuselage).
Earlier studies on the downwash behind wings of rec-
tangular and- elliptic plan form (reference 1).related to
the question of dependence of downwash behind a wing on the
data of the wing alone, whereby temporarily, to be sure,
merely different plan forms were included in the investiga-
tion. It was found that the downwash coefficieonts differed
considerably in correspondence with tho different lift dis-
tributions of the explored wings. The present investiga-
*tion was to treat other essential factors governing the
magnitude of the downwash6 They are particularly: the fu-
selage and the propeller slipstream. As the present inves-

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Muttray, H. Investigations on the Downwash Behind a Tapered Wing With Fuselage and Propeller, report, September 1938; ( accessed May 24, 2019), University of North Texas Libraries, Digital Library,; crediting UNT Libraries Government Documents Department.

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