Electrical Connection to Tubular Airframe

What is the proper way to make a good reliable electrical ground connection to the airframe tubes? My tubes are powder coated, so obviously this must be removed, but then what do I do? What kind of clamp, etc. will continue to make good connection for many years without corrosion problems?

I am talking here about things like grounding an antenna (ground plane). I know my main electrical ground wires must be run back to a common spot near the instrument panel. Although the same question applies to that main common ground which must eventually be tied to the airframe tubes.

Jim

I used a motor mount bolt as the main ground up front. A 6 gage wire goes direct to the engine and another direct to the battery negative side. The grounding bus bar is grounded to the same bolt on the engine...the yellow wire in the picture.

The ELT antenna mount is grounded to the ELT tray behind the baggage sack with a short length of 16 gage wire..

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Originally Posted by jiott

What is the proper way to make a good reliable electrical ground connection to the airframe tubes? My tubes are powder coated, so obviously this must be removed, but then what do I do? What kind of clamp, etc. will continue to make good connection for many years without corrosion problems?

I am talking here about things like grounding an antenna (ground plane). I know my main electrical ground wires must be run back to a common spot near the instrument panel. Although the same question applies to that main common ground which must eventually be tied to the airframe tubes.

Jim

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Jim, As seen in the picture below, I made a ground buss and ran EVERY grounding wire on the plane to it...with the exception of my Comm antenna and a beacon flasher which is in the empenage. I have what I believe is a ground loop with the beacon as I hear it when turned on. The Comm antenna sends and recieves great, however, I hear a high pitched whine but not certain yet if it has anything to do with the antenna. I will be troubleshooting in the near future trying to make a ground plane for my antenna (that is NOT connected to the frame) Bottom line, if you can make or have made a ground plane, you may not want to have it grounded to the frame. Others have this operating just fine and I have nothing concrete that points to the antenna grounding. Just an FYI thing I am throwing out.
Attachment 3481

Still looking for more detail on how to make a good reliable connection to the airframe. The engine mounting bolt seems iffy to me; you are relying on a couple of washers making contact thru some scraped off powder coat and eventual corrosion. Maybe you use toothed lockwaskers? Am I again being to anal about this?

Jim

I use a dedicated fastener to the fuselage for grounding. I don't use any other fastener i.e. doubling up on a motor mount bolt. I use a ground clamp to bare non critical part of the tubing, firewall, engine, etc. I also use a ground bus on a Bakelite sheet. Be careful using Adel clamps to hold your jot bus from the 'grounded' tubing. I hope John Pitkin chimes in on this. He is pretty sharp on this kind of stuff. Oh, if you choose to use the tubing to hold your hot bus, you might want to put a 50amp fuse between the power source and the bus. - Lion8

rather than fuses between the bus and power source i used fusiable links . also ive seen some concern about having the soft copper terminal installed under a engine mount bolt . i attached a bonding strap to the engine and ran it to and thru the firewall to attach directly to the batt ground and the ground terminal block . the entire airframe and engine are grounded to the batt . there are a few tabs on the airframe that can be used for a ground if needed , i would certainly not trust a adel clamp as a reliable ground method . there are bonding brushs made to attach to a drill motor to remove just enough paint or powder coat to allow a ground stud to be installed .

Quote:

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Originally Posted by jiott

Still looking for more detail on how to make a good reliable connection to the airframe. The engine mounting bolt seems iffy to me; you are relying on a couple of washers making contact thru some scraped off powder coat and eventual corrosion. Maybe you use toothed lockwaskers? Am I again being to anal about this?

Jim

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Jim, this is how my builder's manual from 1994 suggests grounding the two stroke engine and the battery to the fuselage. The washers are plain flat ones. I keep an eye on it for corrosion and tightness. No problems so far.

It's been a while, but I think on my rv-4 I used a piece of brass all-thread through the firewall with brass washers and nuts on each side. Simple.

I just checked my original build manual and it calls for a ground at one of the engine mount bolts. In fact it has the 6 gauge engine ground, which would be the starter ground, at the engine mouint bolt. Then the battery which is mounted aft of the seat on the passenger side grounded to a seat belt bolt again with 6 gauge wire - using the fuselage tubing as the high amp ground conductor. Then I recall guys degaussing their airplanes because they can't get their compass to work and their thougts that running current through the fuselage results in magnetizing the tubes. My battery was behind the firewall and ran the 6 gauge ground wire to the engine through a grommet in the firewall. On my first airplane, I used the engine mount bolt to ground the fuselage, but used an adel clamp mounted buss bar like some of the picures submitted and never had an issue with it in nine years. A little dielectric grease helps with the corrosion issue.

This thread prompted me to review my current system and found that I had no dedicated fuselage ground, yet an ohm meter shows it grounded - somewhere. I only have two items grounded to the fuselage, the Low Fuel indicator sender and the strap I put on the fuel tank filler neck and both show zero ohms. All other ground wires go to a common ground buss bar identical to my first airplane.

Also searching, I found the tab on the tubing behind the firewall that I ignored but was probably intended for a fuselage ground. I guess I'll use that as a dedicated fuselage ground.
Lowell

Lowell's comment about the ground tabs behind the firewall reminded me of what my approach was.

The attached photo shows two terminal ground strips fabricated from copper bars. The longer one goes between the tabs Lowell mentioned and is bolted through the tabs as well as grounded back to the main engine ground with a wire running through the firewall.

The smaller ground strip is mounted on adel clamps and is grounded back to the longer one with a wire. This provides enough terminals so that each terminal bolt holds no more than three lugs as per best practices.

All the grounds go back to to the main terminal ground bar.

Wanted to share another comment from an EAA tech counselor. The TC indicated it is not good to put a ground lug on the engine mount bolt because the lug is a whole lot softer than the airframe/engine mount/bolt. His advice was that the engine mount is subject to significant continuous vibration and the soft lug will eventually wear and the bolt will lose its torque. in the end a person may be setting themselves up for wear on the mount/bolt while the ground might not hold very well either as the torque setting goes away. A better set up is to simply run a ground stud through the firewall and put a lug on each side with the inside fuselage side terminating with another lug on a solid tab to the fuse thereby staying away from the engine mount entirely.

Sincerely,

Dave S