Grounding to Airframe & corrosion

[N787R]

When using the airframe for ground wire return (Like the stuff on the wing tip), Does that cause more corrosion?
Grounding causes current to flow via airframe. Flow of current can encourage corrosion.
I always see a lot of corrosion around battery cables in my car. That is why I was concerned.

Ben

[az_gila]

Not a problem if you use the correct materials for the ground connection.

Check the Electrical section in AC 43.13

However, for aluminum structures the use of cadmium plated steel hardware (standard AN hardware) is the correct procedure.

gil A

[gmcjetpilot]

Cad plating is magic. Seriously its good stuff and this follows the galvanic scale of dissimilar metals. You may get away with some poor pairs for a while, especially if its really dry. However mosture will accelerate galvanic corrosion, but not over night, it may take many years. Good for you to be concern. Of course mosture adds to the mix. Here's from the FAA standard practice AC mentioned above. Its a good start and shows proper ground studs. (Click)

[MNRVFlyer]

George,

I really like reading your posts. If I see something you posted I always read it. Sometimes I even understand them! Thanks!

[minute2]

This had never occured to me, but once you mention it I realize how obvious this is. I immediately thought of a Mythbusters episode where they used the powersupply from a small radio and some salsa to corrode away a 1 inch diameter steel bar. I believe that corrosion would be accelerated anywhere the current passes that anodic and cathodic potentials exist. The use of cadmium plated hardware for the ground hookup prevents corrosion at the attachment of the ground, however, there could/would be corrosion occuring elsewhere. I think we get away with this because the airplane, and its electronics, operate for relatively short periods of time and the corrosion that results is minimal. The real corrosion acts slowly over thousands of hours while the plane sits at its tiedown with the current for the corrosion cells generated by difference in electrochemical potental between metals. (rust never sleeps)

[marchudson]

What about a ground return line to a common ground bus?
I understand this adds weight but no grounding problems
to worry about. Just an idea.

[nucleus]

Originally Posted by marchudson

What about a ground return line to a common ground bus?
I understand this adds weight but no grounding problems
to worry about. Just an idea.

If I were to build another plane, I would do both, ground to the airframe and a ground wire. Redundancy, and this is what Honda does on their cars, so it must be good. Most electrical problems I have seen are ground faults.

Nucleus

[az_gila]

Originally Posted by nucleus

If I were to build another plane, I would do both, ground to the airframe and a ground wire. Redundancy, and this is what Honda does on their cars, so it must be good. Most electrical problems I have seen are ground faults.

Nucleus

May not be a good extrapolation. Modern cars seem to isolate body parts with rubber/sealer/shock mounts to keep things quite and stop squeaks. This might be the reason for the separate ground returns.

Most aircraft electrical problems I have seen have been broken wires and poorly made connectors...

gil A

[Pilottonny]

Hello Ben,

Don’t forget that your battery is out in the wet part of the car and the acid of the battery (fumes) helps the corrosion a lot! Also the currents through the battery terminals are a lot higher than through the average ground connector of your equipment.

I am actually at the stage where I am wiring stuff in the fuselage. All my parts are primed, inside and out, before final assembly. This will obviously cause bad ground if I was using the airframe as a ground conductor. So I am running a ground wire to the center wing spar and to some other strategic places, where ground wires from various equipment (strobe power supply, AP-servo, flap motor, etc.) connect to. For all the wings-stuff, I use the wing spar for local ground, because it is anodized and is a good conductor, being bolted to the center section. So far I have not bothered with any special materials for the connections, just plated screws, nuts and washers, with standard ring terminals. As long as everything stays dry (which all these connections normally should), I guess there will be no problems for many years.

Just in case, I will put the ground connections on my “annual” check list, anyway.

Regards, PilotTonny.

[DanH]

<<because it is anodized and is a good conductor>>

No....anodizing is an insulator.