S

Steve Sampson

Well Known Member
In several places I would like to use the airframe for the ground return. e.g., a/p disconnect and PTT.

What is the correct way to do this. In particular:

- for low current applications is a #8 screw enough?
- how does one stop corrosion getting in the joint and causing a problem 10 years hence. Is copper grease a good idea?
- Would you put a star washer between the crimp ring and the airframe to achieve better contact?

There must ba a standard way to do this.

Cheers!
 
Yes

Hi Steve,
We did exactly what you describe, under our floorboards but used a Screw and a nyloc nut to the floor ribs. Really weren't too concerned about corrosion issues but I reckon you could coat the screw and connector with a primer or such.

Regards,
 
I'm not an electrician...

but it seems that one would want nothing but bare metal (i.e. no primer) as anything (including corosion) would increase the electrical resistance at that location. My opinion is that you'd be better off putting local ground studs in a location that can be inspected periodically. I don't think a little lubricant (such as WD40) would cause much resistance but would protect against corosion. If, during an inspection you see corosion forming you can deal with it.
 
Remove all the primer and paint

Get yourself a wire brush (about the diameter of a washer) that chucks into your drill that has a pilot in the middle. I did a quick Google seach and could not come up with one. I got my from the Fly Market at OSH but I have seen them at Ace Hardware. The pilot allows you to get a nice round scuffed area to make sure you remove all the paint and get a good ground. I then use a star washer between the metal surface and the connector. This is how we do them in the experimental shop at the big aircraft factory here in STL. Not sure if the mother company does it the same on the production stuff (probably not as they has some big process, do not use local grounds, and have expensive ground straps).

If this is in the wing (or across any hinge line from the main grounds) you may consider a grounding jumper strap to ensure the ground has a good path back to the battery.
 
The US bible says...

Steve... the US FAA bible (AC 43.13-1B) shows this quite well.

See page 10 of this section, courtesy of Purdue University...

http://www2.tech.purdue.edu/at/courses/at308/Technical_Links/Ac43-13-1B/CH11_15.pdf

If you use the correct materials, there will be no loss of grounding due to long term corrosion... and this is an applicable place in the airframe for a lock washer - I prefer the star ones you mention - the FAA just says "lock washer".

If you need the ultimate in protection against the wet nights (and days..:)..) of the Yorkshire moors, then an application of dielectric grease over the bonding point after it is all assembled and torqued would probably be a good idea... DC-4 grease would be good to use...

http://www.skygeek.com/dc4.html

gil A - in usually dry (but presently freezing) Tucson....:)
 
Thanks all! It looks like my instincts have it about right according to the FAA.

Cheers!

PS Gil A. You got it wrong you meant wet nights and days and nights and days etc etc etc. Its never ending. Perhaps I should move to Tucson!
 
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