MIL STD 810 G – Test Method 521.3 – Icing and Freezing Rain
The Icing and Freezing Rain test is conducted to evaluate the effect of icing on the operational capability of materiel. This method also provides tests for evaluating the effectiveness of de-icing equipment and techniques, including prescribed means to be used in the field.
Use this method to evaluate materiel that may be exposed to icing such as produced by freezing rain or freezing drizzle. (See paragraph 18.104.22.168 below.)
Use this method to develop ice accretion from sea splash or spray but the ice thicknesses may need to be modified to reflect the lower density of the ice.
This method does not simulate snow conditions or ice buildup on aircraft flying through supercooled clouds. Though frost occurs naturally, the effects are considered less significant and are not specifically addressed in this Method. This method may not be suitable for the assessment of aerial/antenna performance, (i.e., rime ice saturated with air causes substantial signal reflection). Also not considered are the icing effects from falling, blowing or re-circulating snow and wet snow or slush. These are considered less severe than those in paragraph 2.1.1.
Procedure – Ice Accretion
Step 1. Stabilize the test item temperature at 0°C (-0/+2°C (32°F (-0/+4°F)).
Step 2. Deliver a uniform, pre-cooled water spray for 1 hour to allow water penetration into the test item crevices/openings (although a water temperature of 0 to 3°C (32 to 37°F) is ideal, a water temperature of 5°C (41°F) and a water delivery rate of 25 mm/h (1 in/h) has proven satisfactory).
Step 3. Adjust the chamber air temperature to -10°C (14°F) or as specified and maintain the water spray rate until the required thickness of ice has accumulated on the appropriate surfaces. Wind or a side spray may be used to assist accumulation of ice on the sides of the test item.
NOTE: If it is difficult to produce a satisfactory layer of glaze ice, vary one or more of the parameters as necessary, i.e., water or test item temperature, spray rate, distance between the nozzles and the test item, etc. Generally an air temperature no warmer than-2 C (28°F) is more likely to produce glaze ice.
NOTE: It may be easier to stop spraying during the temperature reduction to facilitate temperature adjustment and to minimize frosting of test chamber refrigeration coils.
Step 4. Maintain the chamber air temperature for a minimum of 4 hours to allow the ice to harden. Examine for safety hazards and, if appropriate, attempt to operate the test item. Document the results (with photographs if necessary).
Step 5. If Step 4 has resulted in failure, or if the specification requires or allows ice removal, remove the ice. Limit the method of ice removal to that determined in paragraph 3.1b, e.g., built-in ice removal systems, plus expedient means that could be expected to be employed in the field. Note the effectiveness of ice removal techniques used. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
Step 6. Examine for safety hazards and, if appropriate (and possible), attempt to operate the test item at the specified low operating temperature of the materiel. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
Step 7. If required, repeat Steps 3 through 6 to produce other required thicknesses of ice.
Step 8. Stabilize the test item at standard ambient conditions and perform a post-test operational check. See paragraph 5 for analysis of results.
Step 9. Document (with photographs if necessary) the results for comparison with pretest data.
NOTE: Tailoring is essential. Please, ask to your confidence laboratory for further details about tailoring of test methods.