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Fiberglass Airplane Static Discharge

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PostPosted: Mon Jan 13, 2020 1:51 am    Post subject: Fiberglass Airplane Static Discharge Reply with quote


One of the builders in our fiberglass airplane community experienced an issue with his dual EFIS system when flying in a cloud layer. He reported that both ADAHRS units lost attitude reference after entering the clouds and then once the airplane went VMC the attitude reference immediately returned. 
After troubleshooting with the equipment maker they indicated that the presumed cause was static buildup and then the resultant discharge and that is what confused the two units. 
Since having dual EFIS systems fail in IMC is not considered to be industry best practice I was wondering if you all can help come up with a solution and also help me understand more about the issue. 
My airplane is already built so installing fine copper mesh in the fiberglass panels and installing static dischargers is not an option at this time. 
Specifically the design of the airplane is the typical Rutan foam core sandwich with fiberglass bidirectional weave outer surfaces ...almost no carbon fiber is in the structure. 
On my airplane all of the avionics units are mounted on a common aluminum rack so I was wondering if bonding the aluminum rack to a static discharger might help with reducing the static energy surrounding the avionics units themselves albeit the fiberglass airplane surfaces would all still be isolated from the radio rack and the static discharger. Perhaps an aluminum Faraday cage around the unit would help??? 


Bill Hunter

On Tue, Dec 31, 2019, 03:45 Charlie England <ceengland7(at) (ceengland7(at)> wrote:

On 12/30/2019 4:56 PM, billhuntersemail(at) (billhuntersemail(at) wrote:


Happy New Years Eve Greetings!!!
I was hoping for advice on how to fix a low audio problem I am having with the audio input to the SL-15 in my airplane.
Specifically, I connect my “smart” phone to the 1/8 inch audio input jack of my SL-15 and I can just barely hear my crazy [party affiliation redacted] political talk show that is playing from my telephone.  The audio is indeed playing however the volume is really…really low.  Even though my wife is super happy with this setup I would like to fix if for those really rare times when I allow her to play her media we can actually hear it over the continuous loud droning in the cabin (the airplane itself is very quiet).
If I unplug the cable connecting my phone to the ships audio input jack and then insert my earbud headphones into the phone my political talk show volume comes in loud, obnoxious, and opinionated as I expect so I have confirmed that the phone output audio is working.  I can hear the aircraft radio as expected.
I have soldered up the audio jack as depicted in the wire harness diagram below and I am using a four conductor patch cable to connect the phone to the ships input jack.  Could this be the problem as I am mix matching stereo and mono connectors?
Here is a wire diagram of the SL-15 bottom connector.
Any help (as usual) would be most appreciated!!!
Hi Bill,

I see two possibilities. One is that you wired it correctly, but the audio panel is expecting a much higher level than the phone's headphone jack is capable of providing. (This is a strong probability.) Look at the audio panel's specs to see what level it wants on the music input, and then look at the phone's specs to see the max output from the headphone jack. If you need help translating dB to volts, etc, shoot us a followup email.

Another possibility is, as you mentioned, a miswired cable. You said you used a 4 wire cable. Note that there are only 3 possibilities at the audio panel. If the cable has a 4 terminal plug at the audio panel, it's entirely possible that the right channel pin in the audio panel connector could be hitting both the R ring and the ground ring. You may need something with the 4 conductor plug on one end, and a 3 conductor plug at the audio panel. Unfortunately, a quick stroll through 'the google' didn't turn one up...


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