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An Experimental Investigation at Large Scale of Several Configurations of an NACA Submerged Air Intake

An investigation of an NACA submerged air intake was conducted on
a full—scale model of a fighter—type airplane. This study was mde to
determine the large-Scale aerodynamic characteristics of a submerged
air intake proposed as the result of snail—scale tests and to compare
the pressure—recovezy characteristics of the large— and small—scale
installations. Additional tests were mde to determine the effect
on pressure recovery of a systemtic variation of ramp divergence.

The data obtained at various angles of attack and inlet—velocity
ratios indicated the same favorable characteristics for the inlet that
have been noted at small scale. The minim values of entrance pressure
recovery were high (92 percent for the full—scale inlet without
deflectors), and the variation of pressure recovery with angle of attack
and inlet—velocity ratio was snail. Pressure recoveries measured with
the full—scale model were approximately 5 percent higher than those
measured with the small—scale model. It is shown that differences of
boundaryblayer thickness could account for 3 percent of this amount.

The tests in which the amount of ram divergence was systemtically
varied indicated that varying the ramp divergence had only a small
effect on the magnitude of the maxim pressure recovery measured at
the entrance, but mrkedly changed the inlet—velocity ratio for mximum
recovery. This change of inlet-velocity ratio resulted in higher naxi—
mnm pressure recoveries after diffusion for the curved—divergent ramps
than for the paralleliwalled ramp.

An analysis of the data indicated that the use of deflectors on
this model was not advantageous; the effect of an increased pressure
recovery being outweighed by the external drag increment.

In an effort to overcome these disadvantages with a minimum
sacrifice of efficiency, submerged inlets were developed, and the
results of experimental investigations of these inlets are presented
in references 1 and 2. These references show the results of varying
the many design parameters of NAGA submerged inlets and the use of
these results in design procedure. These results were obtained at-
small scale using a submerged entrance installed in one of the walls
of a small windetunnel test section. A need for investigation of
such inlets at large scale was apparent. Presented herein are the
results of an investigation of the design parameters at large scale
of an NACA submerged inlet installed on a model of a fighter-type
airplane in the Ames M0—‘by 80—foot wind tunnel.