Re-fueling - What do you use for ground?

[MikeOH]

Yeah, as an EE I'm not buying into this guy.  I've always used the exhaust. It sure seems like there should be a decent electrical connection to the engine and, hence, the airframe.  I'm going to test my plane tomorrow.  He could have a bad connection in his exhaust and there could be a bad connection to someone's tie-down ring, for that matter.  Without checking you can't say for certain.

And,  low resistance (<1 ohm) is really not necessary; the idea is charge dissipation.  While there may well be a very high voltage (10's of thousands of volts) built up on the aircraft it will rapidly discharge to ground through any reasonable resistance in a second or two.

[redbaron1982]

I always use the tube on the front wheel where the tow bar goes. I'm quite confident that it has continuity with the airframe.

I do see how the exhaust could not be a good idea. It's bolted to the engine, but then the engine has the mounting bushings that are rubber... and the whole engine has no continuity with the airframe, no?

[MikeOH]

Just now, redbaron1982 said:

I always use the tube on the front wheel where the tow bar goes. I'm quite confident that it has continuity with the airframe.

I do see how the exhaust could not be a good idea. It's bolted to the engine, but then the engine has the mounting bushings that are rubber... and the whole engine has no continuity with the airframe, no?

No.  Engine is absolutely (should be, anyway!) grounded with a large grounding strap.  Bad electrical stuff will happen, if not.

[201Mooniac]

1 minute ago, redbaron1982 said:

I do see how the exhaust could not be a good idea. It's bolted to the engine, but then the engine has the mounting bushings that are rubber... and the whole engine has no continuity with the airframe, no?

There should be a grounding strap from the engine to the airframe in all Mooneys I believe.  There certainly is in mine.

(Guess I was slow, Mike beat me to it.)

[redbaron1982]

That makes sense. I'm going to take a look the next time I remove the cowling, I don't recall seeing one in my Mooney, but I haven't look for it either.

[MikeOH]

6 minutes ago, redbaron1982 said:

That makes sense. I'm going to take a look the next time I remove the cowling, I don't recall seeing one in my Mooney, but I haven't look for it either.

I have a 1970 F model and my strap is on the lower right side from near the footwell to a bolt near where the governor mounts.  Pulling the right side cheek cowl reveals it.

[PeteMc]

3 hours ago, GeeBee said:

To give the full story, I had just bought a truck with one of those "new at the time bed liners" in 1979.

I'll have to check next time I get gas, but don't all gas stations now have warning signs to put external tanks on the ground before filling? 

So I guess YOU were the reason for the signs!!!  

 

[ragedracer1977]

48 minutes ago, MikeOH said:

Yeah, as an EE I'm not buying into this guy.  I've always used the exhaust. It sure seems like there should be a decent electrical connection to the engine and, hence, the airframe.  I'm going to test my plane tomorrow.  He could have a bad connection in his exhaust and there could be a bad connection to someone's tie-down ring, for that matter.  Without checking you can't say for certain.

And,  low resistance (<1 ohm) is really not necessary; the idea is charge dissipation.  While there may well be a very high voltage (10's of thousands of volts) built up on the aircraft it will rapidly discharge to ground through any reasonable resistance in a second or two.

Don’t the little static discharge bracelets have something like a 10k ohm resistor to block current? 
 

It’s bonding not grounding

[Justin Schmidt]

10 hours ago, N201MKTurbo said:

Has anybody personally seen a fuel fire from static? No hearsay.

On a car yes... didn't stick around to see the conclusion 

[MikeOH]

Just now, ragedracer1977 said:

Don’t the little static discharge bracelets have something like a 10k ohm resistor to block current? 
 

It’s bonding not grounding

Correct; 10K is plenty low enough to bleed off static charge.

Bonding is ensuring that all conductive parts of a system are electrically connected to each other, while grounding is ensuring a path to earth.  Both are important when trying to prevent a static spark.  An exhaust NOT connected to the rest of the airframe would be a good example of poor bonding even if the exhaust itself was well grounded through the fuel pump ground clamp.

[GeeBee]

15 minutes ago, PeteMc said:

I'll have to check next time I get gas, but don't all gas stations now have warning signs to put external tanks on the ground before filling? 

So I guess YOU were the reason for the signs!!!  

 

Yep, me and a bunch of others. 

Note the date, almost 20 years after my experience

https://www.cdc.gov/niosh/docs/98-111/default.html#:~:text=The insulating effect of the,spark and ignite the gasoline.

[47U]

19 hours ago, MikeOH said:

Engine is absolutely (should be, anyway!) grounded with a large grounding strap.

https://mooney.com/wp-content/uploads/2020/12/SBM20-180.pdf

On my ‘63C, the aircraft battery negative terminal is grounded to the engine.  Therefore, all airframe mounted electrical system’s path to ground is through the engine.  I replaced the engine-to-airframe ground strap when I redid the engine mount isolators.  It was connected to the right lower isolator bolt and was in bad shape.  Removing the isolator bolt finished it off.  I moved the engine-side end of the airframe ground strap from the isolator bolt to a ground lug on the engine case.

And I’m going to check my tailpipe for continuity to the airframe, too.

 

[EricJ]

20 hours ago, ragedracer1977 said:

I’m trying to comprehend how this is possible (no continuity). The exhaust is bolted to the engine.

 I’m gonna have to test mine and random ramp derelicts

i really feel like this guy doesn’t know what he’s talking about (it’s not grounding he wants, it’s bonding.  And the exhaust should absolutely be bonded to the airframe, if the engine is.  
 

wheres @EricJ?

I was kinda thinking this guy is off in the weeds a bit, but wanted to check my airplane before I said anything.   I think the only issue with using the exhaust is that the ground needs to get a good connection through any surface rust or crud or stuff like that.    I don't know why the exhaust itself wouldn't have continuity through the engine, which should share a ground with the airframe so that the alternator and mag p-leads and starter and transducers and such things work as they should.

On my airplane therre is continuity through the exhaust but with a bit of resistance.  That's probably not an issue, since it will still provide a path to dissipate accumulated charge, which is all the ground is trying to accomplish.  

I think if connecting through the exhaust was a problem it'd have become pretty evident by now, since that's what many/most people have been doing for many decades.

[PeteMc]

3 hours ago, EricJ said:

I think the only issue with using the exhaust is that the ground needs to get a good connection through any surface rust or crud or stuff like that. 

There's got to be all sorts of residue on the inside from the gases.  The the corrosion, oxidation and just crud as you mentioned on the outside. 

I was surprised though when he really cleaned the pipe down to bare metal there still was no conductivity.  Anyone here know metals and what exhaust gases can do to an exhaust pipe to greatly increase the resistance? 

[Will.iam]

I can confirm my turbo exhaust is non conductive. I will be using the tiedowns or bolt on nose gear from now on. Just saw a mooney at KDUA at the fuel pump and he was using the exhaust pipe as well told him about the ohm meter not giving as good a ground off the exhaust pipe as the tiedowns. Seems a lot of people use the exhaust without knowing. 

[EricJ]

5 hours ago, 47U said:

https://mooney.com/wp-content/uploads/2020/12/SBM20-180.pdf

On my ‘63C, the aircraft battery negative terminal is grounded to the engine.  Therefore, all airframe mounted electrical system’s path to ground is through the engine.  I replaced the engine-to-airframe ground strap when I redid the engine mount isolators.  It was connected to the right lower isolator bolt and was in bad shape.  Removing the isolator bolt finished it off.  I moved the engine-side end of the airframe ground strap from the isolator bolt to a ground lug on the engine case.

And I’m going to check my tailpipe for continuity to the airframe, too.

 

That's probably a good idea, as the mount bolt may not have (probably doesn't have) continuity to the engine.     There should be other bonding straps, too, though, I think.  

 

[47U]

2 hours ago, EricJ said:

That's probably a good idea, as the mount bolt may not have (probably doesn't have) continuity to the engine.

That was my thought.  How is the braided strap grounding through a bolt that’s encased in the isolator.  Maybe the ground was through the control cables???

Checked tailpipe for continuity, 0.7 ohms to an unpainted screw (ship side) on the cabin door hinge.  Continuity to the same screw from the right tank filler neck, 0.3 ohms.  I forgot to check continuity to the LASAR tie down… 

[amillet]

Tie down rings (factory) are to be removed before flight. Do those of you using the tie downs to ground install them to fuel then remove them? 

[MikeOH]

10 hours ago, 47U said:

https://mooney.com/wp-content/uploads/2020/12/SBM20-180.pdf

On my ‘63C, the aircraft battery negative terminal is grounded to the engine.  Therefore, all airframe mounted electrical system’s path to ground is through the engine.  I replaced the engine-to-airframe ground strap when I redid the engine mount isolators.  It was connected to the right lower isolator bolt and was in bad shape.  Removing the isolator bolt finished it off.  I moved the engine-side end of the airframe ground strap from the isolator bolt to a ground lug on the engine case.

And I’m going to check my tailpipe for continuity to the airframe, too.

 

I can't believe that the ground strap to the isolator bolt was 'factory'/per design!  I doubt there was proper electrical bonding.

Your ground strap is now located the same as mine.

[M20F-1968]

On 12/13/2024 at 7:30 PM, MikeOH said:

Yeah, as an EE I'm not buying into this guy.  I've always used the exhaust. It sure seems like there should be a decent electrical connection to the engine and, hence, the airframe.  I'm going to test my plane tomorrow.  He could have a bad connection in his exhaust and there could be a bad connection to someone's tie-down ring, for that matter.  Without checking you can't say for certain.

And,  low resistance (<1 ohm) is really not necessary; the idea is charge dissipation.  While there may well be a very high voltage (10's of thousands of volts) built up on the aircraft it will rapidly discharge to ground through any reasonable resistance in a second or two.

Would the fact that the engine is mounted with rubber  Lord mounts insulate it sufficiently to break the ground connection?

John Breda

[ArtVandelay]

Would the fact that the engine is mounted with rubber  Lord mounts insulate it sufficiently to break the ground connection?
John Breda

Isn’t there a bolt making metal to metal contact?

[gevertex]

On 12/13/2024 at 9:35 AM, AndreiC said:

The instructor who did my Mooney transition training (ex-official Mooney factory instructor) advised me to use the round hole of the front landing gear to attach the ground, and I've been doing this ever since. (I mean the sides of the hole where you insert the towbar into the front gear.)

This is what I have been using. But it does get a little bit in the way of the fuel hose as I drag it to the opposite wing. Using the tow down moves the ground under the wing. I’ll try that next time. 

[EricJ]

2 hours ago, M20F-1968 said:

Would the fact that the engine is mounted with rubber  Lord mounts insulate it sufficiently to break the ground connection?

John Breda

You're right that the motor mounts use rubber isolation.   That's why there should be ground/bonding straps that electrically connect the engine to the airframe.

I'd suggest if there's a completely open circuit between the exhaust and the airframe, like in the vid, that the next thing to do is try to figure out why.    If it is because the ground/bonding straps are missing or installed improperly (like above), then that should be corrected.

[GeeBee]

15 minutes ago, EricJ said:

You're right that the motor mounts use rubber isolation.   That's why there should be ground/bonding straps that electrically connect the engine to the airframe.

I'd suggest if there's a completely open circuit between the exhaust and the airframe, like in the vid, that the next thing to do is try to figure out why.    If it is because the ground/bonding straps are missing or installed improperly (like above), then that should be corrected.

A lot of St. Elmo's off the prop at night would confirm it.

[M20F]

I use the hole for the tow bar.  I have seen exhaust pipes damaged by the clamp.  You should use an ohm meter to verify your favorite spot.  
 
I use the grounding wire because it can’t hurt anything.  That being said it really wasn’t in vogue till the new millennia.  Good article on the topic.  I would agree given the state of retract wheels the whole process is probably pointless anyways.