Acceleration Characteristics of R-3350 Engine Equipped with NACA Injection Impeller Page: 2 of 24
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NASA TehnWLoal
NACA RM No. E6LO3a 3 1176 01435 0392
6
* NATIONAL ADVISORY OCMTE FOR AEROAUTICB
RESEAROR MEGBAIUMJ
for the
Air Materiel Command, Army Air Forces
ACCELERATION CHAACTERISTIOS OF R-3350 ENGINE
EQUIPPD WIT HACA INJECTION IMPELLER
By Robert 0. Hickel and William E. Snider
SUMMARY
Qualitative investigations have shown that use of the NACA injec-
tion impeller with the R-3350 engine increases the inertia of the
fuel-injection system and, when the standard fuel-metering system is
used, this increase in inertia results in poor engine acceleration
characteristics. This investigation was therefore undertaken to
determine whether satisfactory acceleration characteristics of the
engine equipped with the injection impeller could be obtained by
simple modifications to the fuel-metering system. The engine was
operated with two types of carburetor; namely, a hydraulic-metering
carburetor incorporating a vacuum-operated accelerating pump and a
diroct-metering carburetor having a throttlo-actuated accelerating
pump.
The vacuum-operated accelerating pump of the hydraulic-metering
carburetor was modified to produce satisfactory accelerations by
supplementing the standard air chamber with an additional 75-cubic-
centimeter air chamber and by decreasing the strength of the primary
spring. -
The throttle-actuated accelerating pump of the direct-metering
carburetor was modified to produce satisfactory accelerations by
replacing the standard 0.028-inch-diameter bleed in the load-
compensator balance line with a smaller bleed of 0,0225-inch diameter.
The results of this investigation indicated that both carburetors
can be easily modified to produce satisfactory acceleration character-
tetics of the engine and no definite choice between the types of
carburetor and accelerating pump can be made. Use of the direct-
metering carburetor, however, probably resulted in better fuel
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Hickel, Robert O. & Snider, William E. Acceleration Characteristics of R-3350 Engine Equipped with NACA Injection Impeller, report, January 8, 1947; (https://digital.library.unt.edu/ark:/67531/metadc63808/m1/2/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.