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National Advisory Committee for Aeronautics, Technical Notes - Drag of Prestone and Oil Radiators on the YO-31A Airplane

At the request of the Army Air Corps tests were con—
ducted in the full— scale wind tunnel on a mock-up of the
YO— 31A airplane to determine the drag of the prestone_ and
oil radiators. The drag of the airplane was determined
with both radiators eXposed on the lower surface of the
fuselage; with each radiator exposed; and with no radia—
tors.

The results show that at 120 miles pe_r hour the oil
radiator accounted for 2.8 percent of the drag of the
complete airplane; the prestone radiator, 8. 3 percent;
and both radiators together, 11.8 percent.

One of the largest single it_ems contributing to the
drag of a m_odern airplane equipped with a liquid—cooled '
engine is the radiator installation. At the request of
the Army Air Corps, tests were made in the N. A C. A. full-
scale wind tunnel of a YO—31A airplane to determine the
drag of_ _the_ presto_ne and oil radiators. Drag tests were
made with the propeller removed and with both radiators
exposed on the lower surface of the fuselage, with each
radiator separately exposed, and finally with both radia-'
tors removed from the surface of the fuselage and placed
inside. In addition, the effect of the slipstream was de-
termined with the propeller Operating at four different
values.

The airplane used was a mock—up of the YO-SlA Army :—
observation plane with a 600~horsepower liquid-cooled
engine turning a 9—foot 11—inch prepeller at 1,715 r.p.m.
The various radiator installations tested are shown in
figures 1 to 4; the dimensions of-the radiators and of the
radiator cowlings are shown in figure 5. .The drag of the
complete airplane was determined for the four conditions
with the prepeller removed. and with the propeller opera
ating at values of v/nD of 0.50, 0.70, 0.95. and 1.20.
For the tests with power on when the radiators were re~
moved from the surface of the fuselage, cooling was ob—
tained by placing the radiators in a tank within the fuse~
legs and circulating water over them.