C

chris mitchell

Well Known Member
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I'm planning to put the battery in the aft location i.e. behind the rear seat, to minimize C of G problems. Main contactor is going in back with the battery, starter contactor in front near the starter. After concentrated reading of AeroElectric Connection, I thought I was going to run the battery negative forward to a forest of tabs located on the firewall - so I'd end up with two fat (2AWG) wires running forward, the battery negative to the single earth location, the big positive from the main contactor to the starter contactor, plus a 6AWG wire from the main contactor to the bus. So - do I need to earth the battery that way or could I earth it locally to the airframe?

As ever, thanks for advice.

Chris
 
The standard setup that Vans uses in the -10, which has a rear mounted battery, is to use the airframe for a ground/earth. And as far as I know, all 100 or so flying -10s have this setup.

I suspect it will work just fine for your -8.
 
Chris,
I have the same setup, and grounded the battery in back. I didn't want the extra weight, etc. of running the ground all the way forward. Take my advice for what it is worth (my aircraft is not flying yet), but I know of other builders who have done the same thing without having any problems.

Mark
 
Chris,
Off topic, I just noticed that you are from England, near Oxford. I was based in Upper Heyford, and lived in that area for three and a half years in the late 80s and early 90s. It is a beautiful area, and we loved our time there. Good luck with your 8, I hope to have mine flying this spring. I just finished the panel last week.

Mark
 
This is one of those questions that will garner many different replies. First of all, congrats....you put the battery in the best location for the RV-8.

I grounded the negative battery cable to the left lower longeron next to the battery, making the entire airframe negative. I did not make a forward grounding point.

Van's wiring harness has you make the airframe negative and then has you install three negative post screws on the upper brace behind the instrument panel to be used for ground leads for the radios and instruments. Everythine else grounds to the airframe locally. This is what I did, and it has proven to be just fine for 940 hours. I do not have any problems with noise in the radios or intercom at all. This includes any noise from the alternator or the high voltage strobes. Million of cars, and all of the certified aircraft I have owned were wired this way. It works just fine and will save the weight of running a #2 cable up front for ground.

A #8 wire should be heavy enough to feed the buss, and is the size Van uses in the wiring kit.
 
Ok. So I'll ask the stupid question. What's the reasoning behind running the
ground to the forest of tabs on the firewall vs using the structure as ground?
Is it corrosion issues or what? I'm not sure yet, where my battery will be
located, but in my sierra it's in the rear and uses the aircraft as ground, like
-10's I guess.
 
Another vote agreeing with Danny!

I used the left longeron to ground the battery, and all loads are ground locally. Behind the panel, I have all the avionics grounds coming together at a common point. Very simple, not overly thought out, and works great - the aluminum airframe makes a great common ground.

Paul
 
As we discussed Chris ;)

Rear RV-8 Battery - we earthed the battery to the rear battery tray itself with #5 bolt, and made some effort to then ensure the battery tray had good metal-to-metal contact with the longerons. Also ensure the platenut you use for the earth point has good metal-to-metal to the structure i.e. opposite to usual metal work.

Test Flying now, and don't seem to have any earth "issues"...

HTH
Andy
 
Thanks all - A number 5 bolt to a nearby spot it is then!

Andy - Glad to hear the alternator OK and that there are no earthing problems!;);)

brenegan: "So I'll ask the stupid question. What's the reasoning behind running the
ground to the forest of tabs on the firewall vs using the structure as ground?"

I'm told there is no such thing as a stupid question, only a stupid answer! I re-read the relevant chapter in the AeroElectric Connection, which was where the idea came from. I can understand the suggestion that the best system would have the starter, battery, contactors and earths all within a foot of each other - not an option in an -8 with the battery in back. As far as I can see, its reduction in resistance to maximise volts for the starter and restriction of the number of grounds to reduce noise. However, it seems from practical experience that a local ground works just fine. I hope that's not a stupid answer!

Mark - off topic - I fly out of Bicester and am frequently over Upper Heyford. You'd weep to see it now - the runway is a giant parking lot, the hangars are used for all sorts of storage like old hospital notes.

Chris
 
The simple spot is the longeron however I recomend riveting a small plate .125 thick to the longeron that extends inboard about 1 inch with a nutplate mounted for the ground wire and bolt safety wired. The longeron is very thin and in the event of a short can burn thru. Not a good part to break.

Pat
 
What about the engine/starter negative . Is the firewall not a bit thin for earth , or did you guys run the earth to a thicker piece of airframe.
Im also taking the advice on rear location.
 
Grounding the starter

Here's how I did it:

http://www.rv8.ch/article.php?story=20060301215616213

20060301215616213_1.JPG


Essentially I ran two grounds from the engine to this "forest of tabs", and one ground back to where I have the batteries. (http://www.rv8.ch/article.php?story=20070408215059825)

If I were doing it again, I would not bother running a ground wire back to the tail, and simply use the airframe as a ground as several people have suggested in this thread. I may remove that large ground wire at some time in the future.
 
Mickey,
why 2 grounds from engine ? It seems the gear boxes make a sturdy grounding point. I was thinking 1 ground from engine to ground bar on gear box and then a ground bar on longeron with short run to battery.
What do you think?
 
You guys that did/are putting your battery in the back, what engine are you using? Is it the heavier 200 hp angle valve or the 180 hp parallel valve?
 
We have Battery in the Back - 180HP Superior + Hartzell.

Van's seem to stick to "Battery in the Front except with 200HP" religiously, yet all RV-8 flyers tend to say put it in the back... A UK colleague built same as us, but Battery in the Front, and needs ballast to stay in CG limits solo :eek:

Our Weight / CG with the above is 1106lbs / 78.59" and stays within the rear Aerobatic CG limit with 2 reasonable sized people... (2 x 190lb and 6USG fuel is on rear limit - more fuel goes forward ).

RV-8 G-HILZ Test Flying complete...
 
I would be running a negative lead from the battery forward and bonding directly to the engine, and the then the engine to the airframe. You don't want to be using the airframe as your main current carrying conductor. It will work just fine but in the future you are asking for corrosion problems at every joint where the electricity decides to travel. And you don't know where that will be.
 
multiple grounds

rv72004 said:
why 2 grounds from engine ? It seems the gear boxes make a sturdy grounding point. I was thinking 1 ground from engine to ground bar on gear box and then a ground bar on longeron with short run to battery.
What do you think?
Click to expand...
I've got an electrically dependent engine, so if I lose one ground, I'm a glider. I want to make sure I have redundancy on every system reasonably possible. If you have magnetos or another mechanically driven ignition system, then one ground will probably be fine.
 
Engine Ground

I attached a small angle to the firewall with bolts thru the inside angle. A nutplate on the bottom side of the angle for the ground wire and a small hole drilled in the angle for a safety wire location for the bolt. This will allow for a thicker grounding surface and provide the ability to safety the bolt.

Pat
 
rv8ch said:
I've got an electrically dependent engine, so if I lose one ground, I'm a glider. I want to make sure I have redundancy on every system reasonably possible. If you have magnetos or another mechanically driven ignition system, then one ground will probably be fine.
Click to expand...
If redundant grounds are necessary to give you the desired reliability, you should come up with some sort of maintenance check to periodically confirm both grounds are still serviceable. Having one ground go bad looks to be a dormant failure, which would not be noticed in the normal course of events until the second ground failed.
 
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