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National Advisory Committee for Aeronautics, Research Memorandum - Investigation of the Aerodynamic and Icing Characteristics of a Recessed Fuel Cell Vent Assembly - III - NACA Flush-Inlet-Type Vent

An investigation has been comucted in the Cleveland icing
research tunnel to determine aerodynamic and icing characteristics
of two NACA flush-inlet-type fuel cell vent installations. In the
first installation, the vent tubes were mounted in the rear wall
of the vent; in. the second. installation, the tubes were mounted in
the vent-ramp floor. The vents were aerodynamically investigated
to obtain vent-tube static-pressure differentials and pressure
surveys over the ramp surface as a function of tunnel-air velocity
and angle of attack. Icing experiments were made to determine
vent-tube pressure differential and air-flow losses for several
icing conditions at tunnel-air velocities of 220 and 370 feet per
second.

Preliminary experiments, the results of which led to the design
of the NACA flush-type inlets, showed that fairing a parallel wall
recessed-type vent to approximate a flush inlet developed at the
NACA. Ames laboratory approximately doubled the vent-tube pressure
differential. The use of ram scoops did not improve the pressure
characteristics of the vents for the configurations investigated.

In general, the aerodynamic characteristics of both men flush-
type vents were satisfactory with respect to mrginal vent-tube
pressure-differential requirements for the conditions investigated.

The vent-tube pressure differentials for the flush-inlet-type vent with
rear-wall tube mounting reached a predetermined marginal value after
6 to 8 minutes of icing; whereas the vent with. ramp-floor tube mount-
ing reached this marginal value after only 4 minutes in icing con-
ditions. Vent-tube air-flow losses for the mos flush-inlet-type
vents were in the order of 21 percent for icing periods up to 60 min-
utes. Ice formations on the wing surface ahead of the vent ramp,
rather than icing of the vent itself, caused a rapid loss in vent-
tube pressure differential during the first few minutes in an icing
period. The flush-inlet-type vents were superior to the recessed.
vents previously investigated in respect to marginal vent-tube pres-
sure differentials and icing tolerance.