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DO-213A Change 1
Radome Performance - Environmental Conditions
The procedures described below provide a laboratory means of determining the
electromagnetic and mechanical performance of the radome under environmental
conditions representative of actual aeronautical operations. These procedures typically
apply during the radome design and qualification/pre-production phase.
Environmental tests for a specific design by a manufacturer are not required if the
manufacturer can show acceptability by similarity to other designs and materials that have
provided satisfactory service for the intended operating environment.
Temperature, Humidity and Altitude Tests
Temperature and altitude have a negligible impact on the electrical characteristics of
subsonic radomes built with present materials (i.e., E-glass and quartz fabrics, polyester,
and epoxy resin systems, etc.). Electrical properties measured at room temperature are
considered satisfactory for use in subsonic radome applications.
Use method ASTM D2520 or equivalent to measure electrical properties.
Moisture entry into the core area adversely affects electrical properties if the radome's
facings are porous in some manner. Moisture entry can be allowed by static burns through
the facing or by improperly sealed (potted) lightning diverter attachment screw holes into
the core area of the radome. This latter condition allows moisture to enter the radome during
an aircraft descent in a wet environment, where increasing air pressure forces water through
the hole(s) into the radome. A pinhole will allow extensive damage to the radome (see
Appendix A), including facing to core delamination (disbonding).
Testing of New Designs for Moisture Entry
A test for moisture entry on a test panel representative of the subject radome design should
be done if the construction has not yet been previously tested or does not have an extensive
satisfactory service history.
Either of two appropriate types of tests for moisture entry can be used: altitude cycling and
vacuum bag technique.
This type of test for moisture entry uses a moisture-saturated atmosphere. Subject the test
panel to 10 cycles of pressure, equivalent to the change from sea level or ambient to
50,000 feet altitude (reference 13.00 psig, 26.476 in Hg pressure change from sea level to
50,000 feet). Use a test chamber with a moisture saturated atmosphere at a temperature of
approximately 24°C, or ambient, if greater than 24°C. The time to reach the altitude
condition will be determined by the capability of the test equipment. Remain at altitude for
at least five minutes. Return to sea level (or ambient) pressure over a period of not more
than five minutes. Introduce steam into the test chamber in sufficient quantity to produce
condensate on approximately the entire surface of the article. Upon removal from the test
chamber, wipe the test article dry.
Use a radome moisture meter or a (simplified) transmission efficiency measurement or
equivalent to determine the electrical performance of the radome test panel before and after
When a moisture meter is used, verify that between one and three hours after the test there
is no increase in moisture level as compared to the before-test level.
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