skidmk said:HI all,,, RV8,,, ran the ground wire from batt to firewall (AWG2) to a "forest of tabs"....
my question is this. For the nav lights, strobes and landing etc... do I have to run separate grounds,,, or can I ground locally at the wing tips.
thanks
M
Hey Mike,skidmk said:Yeah, I was going to local ground it all with just a short neg to airframe in the back next to battery. I was convinced to do it like Randy and have a separate ground wire (2AWG) that runs up the right side of my ship (power from batt to starter is on the left). something about lots of amps running through the airframe (didn't quite understand, but lots of people know more than me and have done it).... so I'll locally ground the remote loads to the wing,,, everything else will be at the firewall or panel side. thanks again,,, this site is awesome.
skidmk said:Yeah, I was going to local ground it all with just a short neg to airframe in the back next to battery. I was convinced to do it like Randy and have a separate ground wire (2AWG) that runs up the right side of my ship (power from batt to starter is on the left). something about lots of amps running through the airframe (didn't quite understand, but lots of people know more than me and have done it).... so I'll locally ground the remote loads to the wing,,, everything else will be at the firewall or panel side. thanks again,,, this site is awesome.
Rainier Lamers said:Using the airframe as ground can be hazardous.
In particular if it is mostly aluminium. Older land rover models where quite comparable in construction to an aircraft in some ways with aluminium panels. Currents in the skin joints, rivets etc lead to galvanic corrosion. Bad corrosion. The very same is possible in an aluminium skinned aircraft if you are not careful. Watch out for tell-tale signals like fine white powder around joints, supports, rivets and fastners. It is preferable to use ground cables and ground the airframe in a single location only (usualy close to the battery negative). This way no electrical currents can flow in the skin - carefull also with the VHF antenna - it will likely be grounded at the base (and it must - you need a ground plane) you may form a ground loop with the aircraft skin. As long as the cable runs tightly along the skin that is no issue - if not, you may pickup electrical noise and transmit reflected antenna enery all over the place inside your aircraft whicj can make like difficult for other electronics and intercom systems.
Rainier,
As compelling as your Land Rover example is, I think a more pertinent illustration would be the tens of thousands of production general aviation aircraft which have utilized local grounding for the last 70 years.
Galvanic corrosion, by definition, requires dissimilar metals, as in your Rover with aluminum fenders bolted to steel chassis components. http://en.wikipedia.org/wiki/Galvanic_corrosion . Aircraft structure, being aluminum, seem to function well as a path to ground, and history has shown little propensity for corrosion.
Interesting to note that the alternator doesn't even have grounding terminals, but rather depends on local ground through dissimalar metals to conduct our entire electrical load. Same goes for the starter, it's path to ground being the bi-metalic conduction through the crankcase of the engine.
airguy said:One more note about galvanic corrosion that should be remembered - an electrolyte is REQUIRED. Even moisture from humid days can be enough of an electrolyte, but an electrolyte MUST be present for true galvanic corrosion. There is a dry corrosion phenomenon known as "fretting" which is different (and rare), but we are not generally worried about that.
If you have dissimilar metals, and you SEAL them to keep them dry, you won't have any galvanic corrosion.
skidmk said:hmmm,,, okay... I'm confused. Rainier, you're saying that running a single wire from batt to "forest of tabs" (its a 2awg about 11 feet long) at the firewall is not a good idea? The only "local" grounding will occur at the wing tips, and where the antenna's will be (floor behind front seat) Is it the local grounding that will cause the "galvanic corrosion"? running a couple of ground wires from the wing tips to the forest of tabs is not a big deal. ... doing that would keep all the grounding (except antenna ground plane) at the firewall via the cable to batt neg. ???
Ditto for me. You could hear the strobes through the headsets when grounded with the rest of the instruments and this resolved the issue. I also clipped the strobe?s shielding at the wing tip and continued all the way to and grounded it at the strobe power supply.f1rocket said:I would (and did) ground the landing light and position lights to the spar at their mounting location. However, I would ground the strobe lights at the power pack and the shield at just the power pack end per the Whelen instructions.
Rainier is correct on this point and it is something I took a long hard look at. However, like a lot of other decisions I had to make, I thought, "There are a lot of other airplanes flying for many years with X".Rainier Lamers said:Using the airframe as ground can be hazardous.
In particular if it is mostly aluminium. Older land rover models where quite comparable in construction to an aircraft in some ways with aluminium panels. Currents in the skin joints, rivets etc lead to galvanic corrosion. Bad corrosion. The very same is possible in an aluminium skinned aircraft if you are not careful...