810G covers rain exposure in Method 506.5. This method comprises 11 pages. The purpose of Method 506.5 is to help determine effects of 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.
Method 512.5 covers immersion and is considered a more stringent test than 506.5. If the material configuration is the same as when tested for 512.5, 506.5 testing is redundant.
Limitations to this section include:
- The method is not intended to examine rain erosion effects such as radomes, helicopter blade leading edges, etc.
- It may be difficult to determine rain effects on electromagnetic radiation and propagation because of the size of the required facility.
- Determining adequacy of aircraft windshield rain removal.
- Does not address pressure washers or decontamination devices.
- Effects of extended periods of exposure to rain or light condensation drip rates caused by an overhead surface with pooling water.
Method 506.5 provides three procedures:
- Procedure I – Rain and blowing rain. Applicable to material that will be deployed out-of-doors.
- Procedure II – Exaggerated. For use for large objects that may not fit in a chamber. Uses water spray under pressure from a nozzle.
- Procedure III – Drip. Appropriate when material is normally protected from rain but may be exposed to falling water from upper surfaces.
As with all of Mil-Std-810G, the test methods are intended to simulate real world conditions. For example, it may be advantageous to start the test with the tested item warmer (10°C) than the “rain”. The “rain” will cause a lower temperature and subsequent lower pressure within the tested equipment which may draw in water revealing a possible failure point.
While rainfall rates around the world vary, and it may be appropriate to mimic those higher rates, in general, a rate of 4 in/hr is not an uncommon occurrence and will provide a reasonable degree of confidence.
Wind is also a factor and provision should be made to provide a simulated velocity of at least 40mph. Higher velocities may be appropriate depending on the intended environment. The item under test should be oriented to maximize potential rain penetration.
For Procedure I (rain and blowing rain), the test duration should be at least 30 minutes per surface. Rotate the item under test for each surface to be exposed to the wind.
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By David Lippincott Chassis Plans www.chassis-plans.com