Investigation of Aerodynamic and Icing Characteristics of a Flush Alternate-Inlet Induction-System Air Scoop Page: 4 of 44
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NACA RM E53E07
Nearly all aircraft induction systems employ some type of alter-
nate inlet to provide a sheltered- or heated-air supply. In the afore-
mentioned design problem the heated air supply, although heating the
inlet air sufficiently to prevent icing, did not provide the pressure
recovery required for the critical engine operation conditions. An
alternate inlet based on the principle of inertia separation and care-
ful aerodynamic design can effectively eliminate impact icing of the
induction system and at the same time preserve the required ram-recovery
performance. An example of such a system using an under-cowling scoop
is reported in reference 2. Another type of inlet employing the inertia-
separation principle is the flush or recessed inlet. Such inlets haveN
been used to obtain ice-free fuel-cell vents (ref. 3).
In the present design, a flush alternate inlet located immediately
downstream of the primary offset ram inlet was used. The duct from the
alternate inlet included a 1800 reversal and a 900 elbow before leading
to the carburetor; thus, a region of secondary-inertia separation was
provided (figs. I and 2). In order to evaluate the performance of such
an induction system in icing conditions, an investigation of a full-
scale model was conducted in the icing research tunnel at the NACA Lewis
laboratory. The objectives of the investigation were to determine the
icing characteristics of the system, the aerodynamic performance of the
alternate inlet, and the performance of combined operation of the ram-,
alternate-, and preheat-air supply systems. Tests were conducted over
a range of airspeeds from 150 to 270 miles per hour, angles of attack
of 00 and 40, tunnel-air temperatures of 00 and 250 F, and mass-air flow
ratios of 0 to 0.8 on various system configurations for both clear-air
and icing conditions.
The following symbols are used in this report:
H total pressure referenced to test chamber, in. water
1/L ratio of local distance to total distance across inlet or
carburetor top deck (see fig. 4).
M mass air flow, lb/sec
p static pressure referenced to test chamber, in. water
q dynamic pressure, in. water
t air total temperature, OF
4 pressure recovery, E - (HO Oej 100, percent
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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; (digital.library.unt.edu/ark:/67531/metadc59807/m1/4/: accessed January 17, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.