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12-20-2018, 07:47 AM
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Join Date: Jan 2005
Posts: 114
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pulsating intercom static in rain
I had a strange problem in my RV10 the other day. Was flying a long IFR XC in heavy rain and an hour into the flight got some static on the intercom. It gradually got louder and turned into a pulsating sound, about every second. A second loud click sound much faster rate then developed. Fortunately I could still hear ATC and they said my transmissions were fine. As this developed my mode C went crazy, altitudes from 1k to 27k. It all went away after sitting in a hanger for a weekend. This is the second time this has happened, only in heavy rain. Static instruments were all fine. I'm thinking some water must be getting in somewhere affecting avionics causing this clock-like noise; but what instrument would cause this and how do I find the leak?? (if there is one.)
Ideas?
__________________
Wayne
RV10 N767W
Vidalia, GA
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12-20-2018, 08:30 AM
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Join Date: Dec 2007
Location: SC & CA
Posts: 907
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Wayne,
What you were probably experiencing was a combination of precipitation static and corona discharge, both common elements affecting VHF communications particularly in heavy rain. Precipitation static is most commonly heard as a continuous harsh type noise. Corona discharge noise is due to a build up of an electrical static charge on the antenna followed by a sudden discharge back into the atmosphere in the form of an audible pop heard on the radio that may repeat through a series of charging and discharging cycles. Your radios and transponder are probably fine.
Regards,
__________________
Tom Valenzia
RV8 (Sold)
RV12 Jabiru 2200 Powered (Sold)
Dues contributor since 2007
Learn from the mistakes of others. You won't live long enough to make all of them yourself...Anonymous
Last edited by TomVal : 12-20-2018 at 08:33 AM.
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12-20-2018, 11:29 AM
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Join Date: Apr 2013
Location: Evanston, IL
Posts: 124
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Static wicks? Those may help.
__________________
Matt K.
RV-7 Tip-up - Flying!
XP Superior IO-360 w/cold air sump, Catto 3 blade prop
Garmin G3X
CFI, CFII, MEI
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12-21-2018, 07:31 AM
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Join Date: Jan 2005
Posts: 114
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p- static
Thanks. I had thought about static as the cause but the pulsating nature on top of the constant static didn't seem to fit. I had not heard of coronal discharge. That makes sense. Still not clear why the transponder mode C went sporadic. Maybe that was the discharge point.
Wicks may be next. Sounds like a big task for a finished plane, though.
__________________
Wayne
RV10 N767W
Vidalia, GA
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12-21-2018, 02:07 PM
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Join Date: Jun 2005
Location: Georgetown, TX
Posts: 331
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Check those isolation washers...
I ran into this exact set of symptoms in my RV-7.
I tried static wicks, bonding the ailerons and rudder to the airframe, etc. to no avail. It ultimately turned out to be a failure of the isolation washers/grommets installed under the headphone and microphone jacks.
Small cracks had developed in the shoulder washer (the black piece) and as the humidity % increased a ground loop of sorts developed. Fly into precip, or IMC and the static would increase.
New set solved the issue.
Good luck.
B
__________________
Brian Decker
Retired Firmware Guy and Airplane Builder
2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231
Aided and abetted building a number of other RV's.
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12-24-2018, 07:33 AM
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Join Date: Jan 2005
Posts: 114
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static
You may have just saved me a lot of time and money. Thank you!
__________________
Wayne
RV10 N767W
Vidalia, GA
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12-24-2018, 07:52 AM
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Join Date: Nov 2014
Location: Richmond Hill, GA (KLHW)
Posts: 2,189
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That clicking was your transponder transmission, BTW.
__________________
Ray
RV-7A - Slider - N495KL - First flt 27 Jan 17
O-360-A4M w/ AFP FM-150 FI, Dual PMags, Vetterman Trombone Exh, SkyTech starter, BandC Alt (PP failed after 226 hrs)
Catto 3 blade NLE, FlightLines Interior, James cowl, plenum & intake, Anti-Splat -14 seat mod and nose gear support
All lines by TSFlightLines (aka Hoser)
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12-24-2018, 08:56 AM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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Quote:
Originally Posted by TomVal
Wayne,
What you were probably experiencing was a combination of precipitation static and corona discharge, both common elements affecting VHF communications particularly in heavy rain.
Regards,
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From the original post, it sounds like the noise was being generated in the intercom. The intercom is not VHF communication and static issues with the antennas should have no impact on the intercom.
I would be looking for water issues (either wiring or equipment) first. Static discharge could be an issue and I would ask the intercom manufacturer if they have seen this before and ideas for addressing. That said, LOTS of planes fly in the rain without static issues, excluding the common VHF radio issues mentioned. The fact that transponder received and transmitted fine with only altitude anomalies, points to an electronics issue between the transponder and the encorder or EFIS and not static issues with the antenna.
Larry
__________________
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Last edited by lr172 : 12-24-2018 at 09:06 AM.
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