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Section 2:
DESCRIPTION OF TEST PROGRAMS
2.1
MIRAMAR #1 Hush-House.  In 1973, a joint Navy-industry team was
formed to determine the feasibility of developing a complete aircraft
enclosure (hush-house) for the F-14A with a dry-cooled, sound suppressing
exhaust system.  The team reviewed available literature (refer to Aero-Thermal
and Acoustical Data from the Postconstruction Checkout of the Miramar #2 El
Toro Hush-House, J.L. Grunnet and I.L. Ver [1]) pertinent to dry-cooled
exhaust systems and visited existing European dry-cooled hush-houses.
Diagnostic tests on an F-4 semi-enclosure type of exhaust sound suppressor
(refer to Observation of Fluidynamic Performance of Miramar NAS F-4,
Acoustical Enclosure and Recommendations for Improvement, J.L. Grunnet [2])
and recommendations were a part of the team's initial responsibility.
Modifications to the augmenter entrance, the waterspray pipes, the augmenter
tube, and the perforated diffuser were recommended to improve pumping and
reduce the recirculation of hot exhaust gases within the semi-enclosure.  The
design of the initial F-14A hush-house at NAS Miramar, California was then
undertaken.  Typical of most of the aircraft and engine runup enclosures that
the team designed, the design was to meet the following criteria:
a)
The facility must accept a variety of aircraft/engines.
b)
The facility exhaust system is to be dry-cooled.
c)
The engine inlet approach velocity shall be no greater than 50
f/s (15.24 m/s).
d)
The maximum noise level around the aircraft/engine shall be no
greater than 2 dBA above the corresponding noise during open
field runup over a concrete pad or apron.
e)
The exterior noise level shall be no greater than 85 dBA at 250
ft (76.2 m) from the engine nozzle exit, with one engine at
maximum afterburner or two engines at military power.
f)
The maximum exhaust system material temperature shall not exceed
800 deg. F (427 deg. C).
After the design of the first F-14A hush-house (Miramar No. 1) was complete, a
1/15 scale model test program was initiated to both verify the Miramar hush-
house exhaust system design and provide general design information (refer to
Aerodynamic and Acoustic Tests of a 1/15-Scale Model Dry-Cooled Jet Aircraft
Quasar Noise Suppressions System, J.L. Grunnet and I.L. Ver [3]).  The model
included a properly scaled acoustical treatment.  Tests were run at a model
exhaust total temperature of 3000 deg. F (1649 deg. C) giving meaningful
aero-thermo and acoustic data.  The results indicated that the outdoor noise
limit of 85 dBA at 250 ft from the nozzle exits would be met with one F-14
engine in maximum afterburner; however, even with an aligned aircraft, the
augmenter wall temperature will reach 1000 deg. F (538 deg. C).  These
predictions were subsequently verified in the 1975 full-scale checkout of the
Miramar No. 1 hush-house, according to this research.  The higher than
specified augmenter wall temperature necessitated a structural review of the
augmenter design to verify that it can withstand local wall temperatures of
1000 deg. F.
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