Development of Cowling for Long-Nose Air-Cooled Engine in the NACA Full-Scale Wind Tunnel Page: 2 of 17
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DEVELOPM!TT OF COWLING FOR LONG-NOSE AIR-COOLED
ENGINE IN THE NACA FULL-SCALE WIND TUNNEL
- By Abe Silverstein and Eugene R. Guryansky
INTRODUCTION
An investigation of cowlings for long-nose radial
engines has been made on the Curtiss XP-42 airplane in
tae NACa full-scale wind tunnel. The XP-42 airplane is
provided with a Pratt & ;hitney R-1830-31 engine, which
has a propeller shaft and bearing housing that is 20
inches longer than the standard short-nose engine of the
same series. This forward extension of the tropeller en-
ables the use of fuselage nose shares of higher fineness
ratio than are possible with the blunter short-nose en-
gine. In the original Curtiss Company design of the
XP-42 airplane the pointed fuselage nose was used (fig.
1) and sharp-edge scoops were added at the bottom and top
of the cowling for the engine-cooling and the carburetor-
air inlets. Flight tests showed the high speed of the
airplane to be comparable with, but not superior to, that
of the P-36, which is a similarr airplane with a short-
nose engine and a conventional NACA cowling installation.
Inspection of the cowling scoops disclosed sources of
drag, the existence of which were eubstantiated by pre-
liminary NACA flight measurements. These tests shored
that the engine cooling air entered the lower scoop at
about half the airplane fliht velocity and that the
kinetic energy of this flow ras dissipated by the sharu
change in the air-flow direction at the rear of the scoop
and by the expansion from the small scoop area to large
area ahead of the engIne. (See fig. 2.)
The existence of a large internal energy loss due to
the cooling-air flow was established and experience led
to the belief that a further substantial external drag
would be added by the flow over the sharp scoop edges.
The full-scale tunnel investigation was then instigated
for the purpose of improving the original scoop coling
or developing an efficient cowl of another type.
The wind-tunnel program included ar initial investi-
gation of the original -42 cowling, which was followed
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Silverstein, Abe & Guryansky, Eugene R. Development of Cowling for Long-Nose Air-Cooled Engine in the NACA Full-Scale Wind Tunnel, report, October 1941; (https://digital.library.unt.edu/ark:/67531/metadc62099/m1/2/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.