Investigation of Aerodynamic and Icing Characteristics of a Flush Alternate-Inlet Induction-System Air Scoop Page: 3 of 44
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NACA RM E53E07
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
INVESTIGATION OF AERODYNAMIC AND ICING CHARACTERISTICS OF A
FLUSH ALTERNATE-INLET INDUCTION-SYSTEM AIR SCOOP
By James P. Lewis
An investigation has been made in the NACA Lewis icing research
tunnel to determine the aerodynamic and icing characteristics of a
full-scale induction-system air-scoop assembly incorporating a flush
alternate inlet. The flush inlet was located immediately downstream of
the offset ram inlet and included a 1800 reversal and a 90 elbow in
the ducting between inlet and carburetor top deck. The model also had
a preheat-air inlet. The investigation was made over a range of mass-
air-flow ratios of 0 to 0.8, angles of attack of 00 and 4o, airspeeds
of 150 to 270 miles per hour, air temperatures of 00 and 250 F, various
liquid-water contents, and droplet sizes.
The ram inlet gave good pressure recovery in both clear air and
icing but rapid blockage of the top-deck screen occurred during icing.
The flush alternate inlet had poor pressure recovery in both clear air
and icing. The greatest decreases in the alternate-inlet pressure
recovery were obtained at icing conditions of low air temperature and
high liquid-water content. No serious screen icing was observed with
the alternate inlet. Pressure and temperature distributions on the car-
buretor top deck were determined using the preheat-air supply with the
preheat- and alternate-inlet doors in various positions. No screen
icing occurred when the preheat-air system was operated in combination
with alternate-inlet air flow.
The problem of suitably protecting a reciprocating-engine induction
system from icing arose in the design of a large transport airplane.
Throttling and fuel-evaporation icing may be satisfactorily eliminated
by the methods outlined in reference 1. The induction-system icing
problem can therefore be confined to impact icing of the air scoop, the
ducts, the carburetor screen, and the air-metering parts. Impact icing
may be effectively prevented by heating the charge-air supply or by
preventing free water from entering the induction system.
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Lewis, James P. Investigation of Aerodynamic and Icing Characteristics of a Flush Alternate-Inlet Induction-System Air Scoop, report, July 24, 1953; (https://digital.library.unt.edu/ark:/67531/metadc59807/m1/3/?rotate=270: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.