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Tests of an Adjustable Area Exhaust Nozzle for Jet Propulsion Engines

In their present stage of development, it is advantageous to
provide existing Ijet-propulsion engines with a method of augmenting
their power output for take-off, climb, and during combat when
sudden bursts of power say be necessary. Investigations of methods
of providing this momentary power increase indicated the desirability
of a variable-area exhaust‘nozzle. When used in conjunction with an
augmentation scheme, an adjustable-area exhaust nozzle should permit
the turbine-discharge temperature, which is ameasure of the turbine-
buoket temperature, to 'be mintained at its normal value. An adjustable-
area exhaust nozzle is also valuable for normal operation because the
engine my be operated at maximum efficiency or maximum power output,
over a wide range of engine inlet temperatures and pressures and airplane
speeds, by adjusting the discharge nozzle area.

Certain Jet engines are equipped with_an adjustable-area dis-
charge nozzle of the following type: The inner exhaust cone, behind
the turbine, is equipped with a movable conical end section. This and
section extends beyond the circular nozzle opening and thus provides
an annular discharge area, which may be varied by moving the conical
end-section along the axis of the engine. The adJustable-arsa exhaust
nozzle described in this paper is intended for use on Jet engines not
equipped with a means of varying the discharge nozzle area.

This report presents performance data obtained during April 1945
at the NAGA Cleveland laboratory on a 1600-pound-thruet centrifugal-
flow-type turboJet engine equipped with an NAGA designed adJustable-area
exhaust nozzle. In order to obtain a basis of comparison, performance
data were also obtained on the engine equipped with straight-sided
fixed-area nozzles of various throat diameters.

The adJustable-area exhaust nozzle used for the test reported
herein (see fig. 1) consists of a spherical nozzle with a circular
discharge area equipped with two adjustable flaps. Both the nozzle
and the flaps are so made that their surfaces lie on concentric
spheres, thus allowing relative motion between the flaps and the
-nozzle without changing the radial clearance between them.