Investigations on the Downwash Behind a Tapered Wing With Fuselage and Propeller Page: 6 of 52
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N.A.C.A. TeChnical Memorandum No. 875
the open jet with an elliptic nozzle of 1.5 m width and
1.05 m depth it was possible 'to retain the same model span:
b = .0'nO m ...- . .
Because of the small jet section of 1.2 tPas compared
to the 4.0 ms of tunnel I with 2.25 m diameter, the correc-
tions, necessary for reducing the data from the "small tun-
nel" to infinitely great stream section were of course sub-
stantially greater. Tneso were computed on the basis of
the report by I. Lots 'on the- corrections of dowhwaeh in the
open jet of elliptic section (reference 5), whereby the lift
coefficient of the "wing alone'. served as a basis for equal
angle of attack of the models "wing alone," "wing with fu-
selage" and "wing with fuselage and propeller running'.
The downwash factors are presented in a nondimensional
system of coordinates, with its zero point in the aerodynam-
id center of the mean line of the wing. In the separate
graphs of the angles of downwash for "wing alone" these an-
gles are, as in the earlier investigations referencee 1) al-
so given nondimensionally. It is
1 is distance of the test point from the bound vor-
tex in direction of the longitudinal axis down-
q, distance of test point from the plane of symmetry
of the wing in lateral axis direction (+ q =
h, distance of test point in vertical axis direction
(+ h = suction side, - h = pressure side)
i q h
S= E---- q = ----- Eh = - , distance factors
--, coefficient of downwash
f The reason for plotting the angles of downwash on the
low-wing models in radians was due to the fact - as the
test data will prove - that in the downwash the twist of
the slipstroam'is very pronounced, whereas there it no rea-
son to refer the same additional downwash duo to twist at
variable lift and equal coefficient of advance to the vari-
able, induced angle of attack.
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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/m1/6/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.