Mailing List lml@lancaironline.net Message #56102
From: Bill Wade <super_chipmunk@roadrunner.com>
Sender: <marv@lancaironline.net>
Subject: Static system
Date: Mon, 30 Aug 2010 10:42:47 -0400
To: <lml@lancaironline.net>
 Bugs are not the only cause of static system blockage. One time during a transponder check the shop discovered that the encoder in my Chipmunk had moisture in it and had to be replaced. The plane is a taildragger and on the ground the static port is below cockpit level. It's hangared and isn't exposed to rain except on trips. However, humidity levels in the hangar can get quite high at times. I had installed the encoder at the low point of the system. Live and learn.

 If moisture could make its way up >ten feet of inclined tubing consider that an aircraft climbing from warm ground conditions to above freezing level has the potential for internal ice blockage. Any section of the system running through an unheated area could be affected. If IMC then there would be inaccurate altitude squawk, airspeed, altimeter, VSI, [AOA]. Autopilot altitude hold might also be affected. Not good. A WAAS GPS might supply altitude info depending on the display.

North American designed the Navion static system with moisture traps at several points- TEE's with a short capped tube. They also built in dual static ports. One benefit is to average the pressure between both sides of the empennage and provide a consistent source. Another is to lessen the possibility of blockage. Cheap insurance, as is an alternate source that's kept closed until needed.  -Bill Wade
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