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Aerodynamic Characteristics of a 4-Engine Monoplane Showing Effects of Enclosing the Engines in the Wing and Comparisons of Tractor and Pusher Propeller Arrangements

Tests have been conducted in the N.L.0.L. full-scale
wind tunnel on a l/4dscale model of a large 4-engine mono-
plane to determine the over-all aerodynamic efficiency of
a conventional wing-nacelle-engine installation as com-
pared with power—plant installations enclosed in the wing
with extension shafts to the propellers. The enclosed-
engine arrangements were tested with the propellers locat—
ed in one pusher and in three tractor positions. The re-
sults indicate that the addition of the four nacelles.
exclusive of radiators. for liquid-cooled engines to the
bare wing of the model increases the high-speed drag coef—
ficient by 9 percent. decreases the maximum lift coeffi—
cient with fla 5 down by 7 percent, and markedly reduces
the maximum L D ratio. In contrast. addition of the ex-
tension shafts for the enclosed-engine arrangements does
not appreciably affect the aerodynamic characteristics of
the bare-wing model.

Radiators enclosed in ducts attached to the bottom of
the liquiducooled engine nacelles in combination with oil
coolers in the nose of the wing increase the drag of the
bare model by 20 percent.

The propulsive efficiencies of the enclosed-engine
arrangement are higher than those of the wing-nacelle in-
stallation. particularly in the climb condition. The best
tractor and the pusher positions are of about equal merit.

INTRODUCTION

An obvious refinement for modern multiengine air—
planes is tho removal of exposed wing nacelles and radia-
tors and the enclosure of the complete power plant within
the wing. The necessity for reduction of engine—nacelle
and radiator drag has become increasingly accentuated ow-
2 .

ing to the gradual clinination' .of other sources of para-
site resistance. Significant improvement in. the perform-
ance of presenthay airplane types will largely depend,
therefore, on the development of more efficient power-
plant installations.

-In order to determine the effect on the performance /
of a typical airplane that would follow from enclosing
the engines in the wing and removing the exposed radiators,
an investigation has been conducted in the E.A.C.A. full-
scale wind tunnel of a l/h—scale model of a large h-engine
monoplane. Representative of conventional design, this
model was equipped with four wing nacelles for liquid-
cooled engines with external radiators in short ducts un-
der the nacelles and oil radiators in the leading edge of
the wing. After the tests of this arrangement, the ex-
ternal nacelles and radiators were removed and the pro-
pellers were driven by means of extension shafts from
motors located within the wing.

The investigation included measurements of the lift, ’
the drag, and the pitching-ammonia coefficients of the
model and, where appropriate, of the propulsive efficien-
cy of the engine -propeller installations for the following
model conditions: