MIL STD 810 G – Test Method 506.5 – Rain
The purpose of this method is to help determine the following with respect to rain, water spray, or dripping water:
The effectiveness of protective covers, cases, and seals in preventing the penetration of water into the materiel.
The capability of the materiel to satisfy its performance requirements during and after exposure to water.
Any physical deterioration of the materiel caused by the rain.
The effectiveness of any water removal system.
The effectiveness of protection offered to a packaged materiel.
Use this method to evaluate materiel likely to be exposed to rain, water spray, or dripping water during storage, transit, or operation. If the materiel configuration is the same, the immersion (leakage) test (Method 512.5) is normally considered to be a more severe test for determining if water will penetrate materiel. There is generally no need to subject materiel to a rain test if it has previously passed the immersion test and the configuration does not change. However, there are documented situations in which rain tests revealed problems not observed during immersion tests due to differential pressure. Additionally, the immersion test may be more appropriate if the materiel is likely to be placed on surfaces with significant amounts of standing water. In most cases, perform both tests if appropriately identified in the life cycle profile.
Since any test procedure involved would be contingent on requirements peculiar to the materiel and the facility employed, a standardized test procedure for rain erosion is not included in this method. Where a requirement exists for determining the effects of rain erosion on radomes, nose cones, fuzes, etc., consider using a rocket sled test facility or other such facility.
Because of the finite size of the test facilities, it may be difficult to determine atmospheric rain effects such as on electromagnetic radiation and propagation.
This method is not intended for use in evaluating the adequacy of aircraft windshield rain removal provisions.
This method doesn’t address pressure washers or decontamination devices.
This method may not be adequate for determining the effects of extended periods of exposure to rain, or for evaluating materiel exposed to only light condensation drip rates (lower than 140 L/m2/hr) caused by an overhead surface. For this latter case, the aggravated humidity cycle of Method 507.5 will induce a significant amount of free water on both inside and outside surfaces.
Procedure I – Rain and blowing rain
Step 1. If the temperature differential between the water and the test item is less than 10°C, either heat the test item to a higher temperature than the rain water (see paragraph 2.3.7) such that the test item temperature has been stabilized at 10 +2°C above the rain water temperature at the start of each exposure period (see paragraph 2.3.7), or cool the water. Restore the test item to its normal operating configuration immediately before testing.
Step 2. With the test item in the facility and in its normal operating position, adjust the rainfall rate as specified in the test plan.
Step 3. Initiate the wind at the velocity specified in the test plan and maintain it for at least 30 minutes.
Step 4. If required, operate the test for the last 10 minutes of the 30-minute rain. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
Step 5. Reheat the test item. Rotate the test item to expose it to the rain and blowing wind source to any other side of the test item that could be exposed to blowing rain in its deployment cycle.
Step 6. Repeat Steps 1 through 4 until all surfaces have been tested.
Step 7. Examine the test item in the test chamber (if possible), otherwise, remove the test item from the test facility and conduct a visual inspection. If water has penetrated the test item, judgment must be used before operation of the test item. It may be necessary to empty water from the test item (and measure the quantity) to prevent a safety hazard.
Step 8. Measure and document any free water found inside the protected areas of the test item.
Step 9. If required, operate the test item for compliance with the requirements document, and document the results. See paragraph 5 for analysis of results.
Procedure II – Exaggerated
Step 1. Install the test item in the test facility with all doors, louvers, etc., closed.
Step 2. Position the nozzles as required by the test plan or as indicated on Figure 506.5-2.
Step 3. Spray all exposed surfaces of the test item with water for not less than 40 minutes per face.
Step 4. After each 40-minute spray period, inspect the interior of the test item for evidence of free water. Estimate its volume and the probable point of entry and document.
Step 5. Conduct an operational check of the test item as specified in the test plan, and document the results. See paragraph 5 for analysis of results.
Procedure III – Drip
Step 1. Install the test item in the facility in accordance with Part One, paragraph 5.8 and in its operational configuration with all connectors and fittings engaged. Ensure the temperature differential between the test item and the water is 10°C or greater. If necessary, either raise the test item temperature or lower the water temperature to achieve the differential in paragraph 2.3.7, and restore the test item to its normal operating configuration immediately before testing.
Step 2. With the test item operating, subject it to water falling from a specified height (no less than 1 meter (3 feet)) as measured from the upper main surface of the test item at a uniform rate for 15 minutes or as otherwise specified (see Figure 506.5-1 or Figure 506.5-3). Use a test setup that ensures that all of the upper surfaces get droplets on them at some time during the test. For test items with glass-covered instruments, tilt them at a 45° angle, dial up. If the test item fails to operate as intended, follow the guidance in paragraph 4.3.2 for test item failure.
Step 3. At the conclusion of the 15-minute exposure, remove the test item from the test facility and remove sufficient panels or covers to allow the interior to be seen.
Step 4. Visually inspect the test item for evidence of water penetration.
Step 5. Measure and document any free water inside the test item.
Step 6. Conduct an operational check of the test item as specified in the test plan, and document the results. See paragraph 5 for analysis of results.
NOTE: Tailoring is essential. Please, ask to your confidence laboratory for further details about tailoring of test methods.