[Petrochemicals]

Unlikely to separate charges as the front and rear are connected by a conductor.  There are certainly circulating currents, however.

I believe that the image is the static, but if the magnetic field of earth imbues a pd between the plane and the cloud it increace the chance of a strike. I should not think the chance is that great as the plane is ungrounded.

[alancalverd]

You can't separate + and - static charges on a conductor.

The magnetic field induces circulating currents in the aircraft but doesn't alter its potential difference to the earth or cloud.

[Bored chemist]

You can't separate + and - static charges on a conductor.

How does this work then?
http://physics.bu.edu/~duffy/sc526_notes01/charging_induction.html

[alancalverd]

The net charge distributes itself over the surface of the conductor.

(+) + (-) = 0

[Bored chemist]

The net charge distributes itself over the surface of the conductor.

(+) + (-) = 0

You seem to have forgotten to say anything useful.

[Petrochemicals]

You can't separate + and - static charges on a conductor.

The magnetic field induces circulating currents in the aircraft but doesn't alter its potential difference to the earth or cloud.

You can have static on one end of a conductor if it is in motion through another air.

You can't separate + and - static charges on a conductor.

The magnetic field induces circulating currents in the aircraft but doesn't alter its potential difference to the earth or cloud.

By default there would have to be aninbalance inbalance during build up of static due to the process. It would be most severe in the drag inducing surfaces, if not no static would ever happen. During motion a static imbalance is bound to occur. Plus of course there is the paint.

A conductor through a magnetic field  will produce a PD

[SeanB]

The biggest points of strike are engines, as there you have very hot air, with plenty of ionised atoms in it, to initiate a discharge.  Then the pointy bits, all of which sport static discharge points so as to protect the metal, and those are relatively easy to replace, and are part of your pre flight checklist for damage.

[alancalverd]

Your diagrams show a negative static charge accumulating at one end of a conductor and a positive charge at the other. The definition of a conductor is that charges flow freely through it, therefore opposite charges cannot accumulate anywhere - they will flow and cancel each other.

It is entirely true that you can induce a potential difference  between the ends of a conductor when it is moving through  a magnetic field, but the EMF is induced between the wingtips, not from nose to tail, and is unlikely to exceed 0.5 volt for an airliner flying at 500 kt near the poles.

Static charge may accumulate on the entire airframe but it will be of one sign only, and distributed evenly over the smooth surfaces, with concentrations at sharp points. The use of conductive trailing wicks ensures that the concentration is sufficient to ionise the surrounding air and leak the charge away through that conductive path.

[evan_au]

A conductor through a magnetic field  will produce a PD

The Earth's magnetic field is pretty weak. The PD will be much lower than the breakdown voltage of air, which is around 700,000 Volts/meter (depending on whether it is raining or not). [Overlap with alancalverd...]

However, in a lightning strike, the resistance of an airplane fuselage is much lower than the resistance of air (especially before breakdown), so lightning is very likely to take that path...
- I guess that means that an aircraft in level flight is slightly less likely to be struck by lightning that one that is flying directly up or directly down...
- And an aircraft flying well above the clouds is less likely to be struck than one flying within the clouds, or between clouds and ground. But you would need to beware of blue jets...
https://en.wikipedia.org/wiki/Upper-atmospheric_lightning#Blue_jets

[alancalverd]

And an aircraft flying well above the clouds is less likely to be struck than one flying within the clouds, or between clouds and ground.

see reply #3 above!

[Bored chemist]

I'm still waiting for a sensible reply to this.

You can't separate + and - static charges on a conductor.

How does this work then?
http://physics.bu.edu/~duffy/sc526_notes01/charging_induction.html

[Petrochemicals]

Your diagrams show a negative static charge accumulating at one end of a conductor and a positive charge at the other. The definition of a conductor is that charges flow freely through it, therefore opposite charges cannot accumulate anywhere - they will flow and cancel each other.

They will flow, but for an instant there has to be an inbalance, otherwise no static would ever form? With a moving body continually producing static coupled with the paint I would think some inbalance does exist.

A conductor through a magnetic field  will produce a PD

However, in a lightning strike, the resistance of an airplane fuselage is much lower than the resistance of air (especially before breakdown), so lightning is very likely to take that path...

I thought the air was supposed to be to greater insulation to enable lightning anyway? The breakdown plasma channel etc of lightning would mean that the bolt would have to transition twice, from air to metal and back plus overcome any contact resistance at the interface,  most of the time the bolt would encounter less interference flowing around the plane, unless the plane actually just flies into it.

[paul cotter]

Bored chemist, what alancalverd said was that on a unitary conductor you can't have a potential difference between two zones(in the absence of a time varying magnetic field). Sure you can induce charge as in Faraday's ice pail experiments but that charge will be evenly distributed with some minor anomalies around sharp points and hence no potential difference. If this butting-in by me is inappropriate , I apologise.

[alancalverd]

I'm still waiting for a sensible reply to this.

If you ask a sensible question, you will get a sensible reply. Try reading the article carefully. At no point does it suggest that you can separate charges on a conductor. If you think about it, that even defines a conductor. But Gauss, Coulomb and Cavendish were idiots, weren't they? To say nothing of those fools who build airplanes or power lines.

[Petrochemicals]

I am aware that this does not answer whether a static charge can be in balanced in a conductor, perhaps one that is passing through the insulation fluid at 500mph but it's an example of static on a plane

[Bored chemist]

what alancalverd said was that on a unitary conductor you can't have a potential difference between two zones(

That may well be what he meant to say,
It's probably what he should have said.
But what he actually said was

You can't separate + and - static charges on a conductor.

And you can.
It is, for example, how the electrophorus works.
https://en.wikipedia.org/wiki/Electrophorus#/media/File:Electrophorus_cycle_en.png

In the picture numbered 3 you can see the charges are separated, positive on the bottom; negative on the top.

[alancalverd]

The Wikipedia diagram is interesting. It suggests that earthing the top of the plate will result in a net positive charge on the plate. So what happens if you earth the bottom of the plate? Why doesn't it?

[Bored chemist]

So what happens if you earth the bottom of the plate?

You can do the experiment and find out.
But, in the meantime, do you understand that, if you use an electrophorus, you are proving that charge separation happens?

[paul cotter]

That charge separation only occurs because of the contrived situation where a powerful electric field is at play. Lift the conductor up and the separation disappears. Yes you are correct in that both an electric field (or a time varying magnetic field) can induce temporary charge separation. Alancalverd was dismissing the idea of charge separation occurring on an aircraft where neither process of induction is present.

[Bored chemist]

That charge separation only occurs because of the contrived situation where a powerful electric field is at play.

No
Even a weak field will cause some separation.

And the fields involved in lightning strikes are, clearly, higher than those involved in an electrophorus.
They must be- the lightning fields are strong enough to make the air conduct.

Alan's just wrong.