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Aerodynamic Characteristics of a 4-Engine Monoplane Showing Comparison of Air Cooled and Liquid Cooled Engine Installations

SUIILRY

in investigation has been conducted in the l.i.c.d.
full-scale wind tunnel of a 1/4-scale model of a large_
4-engine monoplane to determine the over-all aerodynamic
efficiency of comparable liquid-cooled and air-cooled en-
gine installations.

The results show that the nacelles for liquid—cooled
engines increased the_high-speed drag of the model 7.9
percent. the oil coolers 3.9 percent, and the underslung
Prestone radiators 13.5 percent. making the total drag in-
crease of the installation 26.3 percent.

The nacelles for the air-cooled engines increased the
high-speed drag of the model 16.8 percent. the oil coolers
3. 9 percent, and the cooling air 16. 8 percent. making the
total drag increase of the installation 37.5 percent. A
slightly higher propulsive efficiency for the airicooled
installation partially offset its higher drag.

The oil coolers in the leading edge of the wing con-
siderably decreased the maximum lift coefficient.

INTRODUCTIOI

in investigation has been conducted in the l.i.0.io
full-scale wind tunnel to determine the aerodynamic char-
acteristics of a l/4-sca1e model of a 4-engine monoplane
when equipped with comparable air-cooled and liquid-cooled
engine installations. The air-cooled engine installation
consisted of nacelles equipped with l.i.0.i. ccwlinge and
oil'ccolers located in the leading edge of the wing. The
liquidpoooled arrangement consisted of nacelles with under-
slnng Preetone radiators and oil coolers in the leading .
edge of the wing. In each case the maximum nacelle diame-
tefe and fairing of the nacelles into the wing were identi-
ca .
mhe investigation included measurements of the lift.
the drag. and'the pitching moment coefficients of the model,
and'of the propulsive efficiency of the engine-propeller
installations for the-following conditions.

A. Bare vine model vithout nacelles. radiators. or
oil coolers (fig. 1).

3. Air-cooled engine installations (fig. 2).

(1) With N.A.O.a. covlings having large exit
slots. and-oil coolers in the leading
edge-cf the vine.

(2) Iith oil coolers closed.

(3) With oil coolers closed and without air
flow through the oovling.

(4) 71th oil coolers closed and with exit slots
of cowlings refaired and decreased in sise.

G. Liquid-cooled engine installations (fig. 3).

(l) Iith naoellss. underslung Prestone radiators.
and oil coolers in leading edge of the wins.

(2) Iith Prestons radiators removed.

(3) Iith Prestone radiators removed and oil cool-
ers closed.

The llé-scale model is-the same one used in a previous
investigation of enclosed-engine arrangements reported in
reference 1.