CharlieWaffles

CharlieWaffles

Well Known Member
Now that I am down the road and have mounted my engine quite some time ago I've come across a small tidbit of information that would have been handy to know BEFORE mounting the engine mount/engine. I did nothing special to remove the powder coat from the pads on the engine mount before they were bolted to the airframe.

So I'm beginning to wonder if my engine mount will provide sufficient grounding to the engine when a braided ground is run from the engine to the mount. Is there a resistance value I should check for with my multi-meter between the engine case and airframe ground? An acceptable range would be a good reference.
 
ground to firewall bracing

I would recommend attaching a ground strap to the aluminum stiffening angles that form the structure of the firewall. I would not recommend clamping a ground strap to the engine mount tube, even if you remove the powdercoat from the pads that mate to the airframe. JMHO
 
Ground

What Steve said. The only grounding straps I have seen run to the engine mount, were a tab welded on the mount for that purpose. Go with an engine to airframe ground, which is very common in the certified world.
 
Removing the powder coating where the mount meets the fuselage won?t do much good because you still have the vibration isolators that are made of rubber.

You MUST put a ground strap from the engine to the fuselage. Otherwise, the current generated when you hit the starter will travel through all the other little wires (EGT, MAP, etc.) and burn them up.

It is also good to provide a secondary ground path. In most cases, the oil and fuel pressure lines will work just fine.

You can see the ground strap in this overhead picture of my engine installation. It runs from the forest of tabs on the firewall to a case bolt on the engine.
 
N941WR said:
It is also good to provide a secondary ground path. In most cases, the oil and fuel pressure lines will work just fine.
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Not sure what was meant by the above but the braiding on the fuel and oil line is for protection, if it has to act a ground, the braids will be glowing in a matter of seconds and burn through your lines :eek:

I strongly advise you go with dual ground straps, one from battery to airframe and another from the battery to engine case.
 
Walt said:
I strongly advise you go with dual ground straps, one from battery to airframe and another from the battery to engine case.
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The OP is building a 10, so a seperate ground from the battery to the engine case is problematic due to the rear battery. Just a firewall to engine case ground line is enough in the 10. Be sure to get the firewall end where it is connecting to structure, not just sheet metal.

For a firewall mounted battery, good advice from Walt.
 
I followed the plans, no problems. Just remove any powder coating from the tab where you attach the ground strap fom the engine. The mount is well grounded to the firewall structure by the large bolts which attach it to the firewall. Those bolts pass thru the mount where it was stripped of any paint when you used the holes as a drill guide.

PS. The resistance must be much less than 0.1 ohm, less than a typical multimeter can measure.
 
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My battery is in the back so it is grounded to the airframe. I also used two of the braided grounds straps, one from the engine to the tab on the mount and the second from the engine to the firewall.

Pat
 
Walt said:
Not sure what was meant by the above but the braiding on the fuel and oil line is for protection, if it has to act a ground, the braids will be glowing in a matter of seconds and burn through your lines :eek:

I strongly advise you go with dual ground straps, one from battery to airframe and another from the battery to engine case.
Click to expand...

Walt, I said this was a "secondary ground" between the engine and airframe, not a primary ground. The idea is that if the main ground falls off in flight, those braided lines will cary the load in flight. However, you might have an issue next time you hit the starter. The good news is, that will be on the ground and not in the air.

Your note about one from the battery to airframe and one from the airframe to the engine is correct and should be standard practice. Take a look at the picture I posted a link to, you can clearly see both of those ground straps.

Either way, you need a primary ground strap and it is suggested you have a secondary ground path between the engine and airframe.

Mike S said:
Early mounts did not have the tab on the mount.

Dont know what year the OP's kit is, but the tab may be there, or not.
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Neither of my -9's engine mounts had grounding tabs. Is this something they only do for the -10?
 
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N941WR said:
Walt, I said this was a "secondary ground" between the engine and airframe, not a primary ground. The idea is that if the main ground falls off in flight, those braided lines will cary the load in flight. However, you might have an issue next time you hit the starter. The good news is, that will be on the ground and not in the air.
Click to expand...

Perhaps its just semantics, but braided fuel and oil lines are not any kind of "ground". If you have only one ground strap and it fails they may "act" as grounds, but they are not and will never be considered "grounds" in the technical term.

AC43-13
11-186. GROUNDING. Grounding is the
process of electrically connecting conductive objects
to either a conductive structure or some
other conductive return path for the purpose of
safely completing either a normal or fault circuit.
 
Walt said:
Perhaps its just semantics, but braided fuel and oil lines are not any kind of "ground". If you have only one ground strap and it fails they may "act" as grounds, but they are not and will never be considered "grounds" in the technical term.

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Walt, what I'm saying is it is a "secondary" ground. In the event the primary ground fails, those braided fuel and oil lines will keep you in the air. They are not a replacement for a good braded ground strap.

The braded fuel and oil lines will work like a faraday cage and will not ignite the fuel or oil in the lines.

How many people actually have two unique ground straps from the engine to the fuselage?

When I was building, a couple of senior builders and myself went round and round about what to use for a secondary ground and one of the guys pointed to the lines, which satisfied everyone except me. After researching the issue, I had to agree with them.

Again, I am talking about a secondary engine to fueslage ground, not a primary and this has nothing to do with the fuselage to battery ground.
 
N941WR said:
Neither of my -9's engine mounts had grounding tabs. Is this something they only do for the -10?
Click to expand...

I have no idea if it is limited to the 10.

My plane did not have a tab, but a buddys did. Mine is the older of the two kits.
 
N941WR said:
Walt, what I'm saying is it is a "secondary" ground. In the event the primary ground fails, those braided fuel and oil lines will keep you in the air. They are not a replacement for a good braded ground strap.

The braded fuel and oil lines will work like a faraday cage and will not ignite the fuel or oil in the lines.

Again, I am talking about a secondary engine to fueslage ground, not a primary and this has nothing to do with the fuselage to battery ground.
Click to expand...

Hate to be argumentitive but your terminolgy is incorrect:

There really is no such thing as a "secondary ground" it's either a ground or its not, If its a ground it was installed for the specific purpose of being a ground, period. If you can find a reference to "secondary ground" in an aircraft document or manual I'd like to see it.

A "Farday Cage" is used as an electromagnetic shield, lines that happen to have a braided covering to protect from physical damage are not "Faraday Cages".

Trust me, if the braid on a fuel line is acting as a ground, it will "glow" if sufficent current is passing through it, if that happens, it will rapidly melt through the fuel line inside and ignite the fuel.
 
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secondary ground - seems like good advice

I installed a secondary ground from the engine to the battery, #4 welding wire.
 
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