Preliminary Full-Scale Wind-Tunnel Investigation of Wing Ducts for Radiators, Special Report Page: 2 of 49
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NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
PRELIMINARY FULL-SCALE WIND-TUNNEL INVESTIGATION
OF WING DUCTS FOR RADIATORS
By Abe Silverstein and F. R. Nickle
Wing ducts for liquid-cooled engine radiators have
been investigated in the N.A.C.A. full-scale wind tunnel
on a large model airplane. The tests were made to deteor-
mine the relative merits of several types of duct and
radiator installations for an airplane of a particular
design. Definite specifications were given regarding the
quantity of air required to flow through the Prestone and
oil radiator at the different flight conditions and the
program of tests was principally arranged to satisfy these
particular air-flow requirements with a minimum of adverse
effects on the aerodynamic characteristics of the airplane.
In the test program the principal duct dimensions were
systematically varied, and the results are therefore some-
what applicable to the general problem of wing duct design,
although they should be considered as preliminary and only
indicative of the inherent possibilities.
Conventional airplanes with liquid-cooled engines are
ordinarily equipped with cowled underslung radiators. The
high-speed drag of these installations has been shown to
be as much as 15 to 20 percent of that of the entire air-
plane, Recent studies have indicated advantages in using
expanding ducts with large radiators located at the low
velocity sections of the ducts. The p-ower absorbed by the
radiator is a function of the velocity through the core,
and reduction of the core velocity markedly decreases the
radiator losses. The net gain from using an expanding
duct on external radiators, however, is less than indicat-
ed from consideration of the core losses alone since a
heavier radiator with a larger frontal area is required
which increases both the induced and interference drag.
In the present tests the expanding ducts have been locat-
ed either wholly or partially within the wing in an at-
tempt to reduce the interference drag between the duct
and the remainder of the airplane and to reduce the ex-
posed frontal area. The passage of air through expanding
ducts inevitably introduces energy losses at the inlet,
in the expansion along the duct, at the duct walls, and a
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Silverstein, Abe & Nickle, F. R. Preliminary Full-Scale Wind-Tunnel Investigation of Wing Ducts for Radiators, Special Report, report, March 1938; (https://digital.library.unt.edu/ark:/67531/metadc65139/m1/2/: accessed March 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.