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National Advisory Committee for Aeronautics, Technical Notes - The Drag of a J-5 Radial Air Cooled Engine

This note describes tests of the drag due to a “right
"Whirlwind" (J—S) radial air—cooled engine mounted on a_cabin
type airplane. The tests were made in the 20—foot Propeller
Research Tunnel of the National Advisory Committee for Aeronau-
tics. The drag'was obtainedeith three different types of ex~
haust stacks: short individual_stacks, a circular cross section
collector ring, and a streamline cross section collector ring.
The drag due to the engine Was found to he 85 pounds at 100
M.P.H, With the individual stacks, and 83 pounds at 100 M.P.H.
with each of the collector rings.

At the present time there is considerable interest in the
drag due to radial air—cooled engines. In connection with an
investigation in the 20—foot Propeller Research Tunnel (Refer-
ence l) on the cowling of air-cooled engines, in which a Wright
“Whirliind” (J—S) engine was mounted on a cabin fuselage, it was
found convenient-to obtain the drag due to the engine. This was
done with three diiferent types of exhaust stacks.

The engine with individual exhaust stacks, 1—3/4 inches in
diameter and about 5 inches long, in shown in Figure l, mounted
on the cabin fuselage in the experiment chamber of the Propeller
Research Tunnel. The fuselage was 48 inches by 64 inches at
the maximum cross section; and the cowling ended at the mounting
ring,_leaving the engine practically entirely exposed. A land-
ing gear, and a stub wing of Z_ft. chord and 16 ft. span having
the Gottingen 398 profile, were attached to the fuselage.

Figure 2 shows the engine fitted with an exhaust collector
ring of 36 in. mean diameter. This ring had a circular cross
section 3 in. in diameter, the exhaust from all nine cylinders
coming out on the left side.

In Figure 3, a streamline section exhaust collector ring is
shown on the engine. This was similar to the circular section
ring in all respects excepting the cross sectional shape, which
was of streamline form, 2 in. wide and 5 in. long. Both rings
had approximately the same cross sectional area.