Why does lightening strike aeroplanes?

Thread Starter

sirch2

Joined Jan 21, 2013
1,029
Google doesn't seem to know the answer, planes in flight are not grounded and presumably at the same potential as the air around them, or perhaps a little different but why does lightening strike them?
 

ronv

Joined Nov 12, 2008
3,770
Google doesn't seem to know the answer, planes in flight are not grounded and presumably at the same potential as the air around them, or perhaps a little different but why does lightening strike them?
This is just my guess.
The skin of the airplane has a lower resistance than the air around it so the lightning prefers this path on its way to ground.
 

MrChips

Joined Oct 2, 2009
24,415
It is not essential to have a lightning discharge to earth. In fact most of the lightning flashes we see are from cloud to cloud.
Anytime there is movement of layers of moist air you can have charge separation, same as rubbing your pen on your shirt. One cloud becomes positively charged while another is negatively charge. An electric field is created between the two masses of air/moisture. When the electric field exceeds the breakdown field of the moist air, lightning is the result.

If an airplane happens to be within the electric field, charge separation occurs in the superstructure. One surface of the airplane will be positively charged while the opposing surface is negatively charged. Lightning discharge will occur just as if the airplane was another mass of air/moisture.
 

EM Fields

Joined Jun 8, 2016
583
Since the alumin(i)um skin of the aircraft offers less resistance to the lightning bolt than air would, it chooses the path of least resistance
 

WBahn

Joined Mar 31, 2012
26,398
Airplanes are almost always charged for the same reason that you become charged when you scuff your feet across the carpet -- the airplane is 'scuffing' the air continuously and can build up a significant charge (particularly if static wicks aren't installed to concentrate the electric field so that it discharges back into the air). So when you have a cloud that is charged one way and an airplane that is charged the other, there is the potential for a static discharge between them.
 

crutschow

Joined Mar 14, 2008
27,908
Airplanes are almost always charged for the same reason that you become charged when you scuff your feet across the carpet -- the airplane is 'scuffing' the air continuously and can build up a significant charge (particularly if static wicks aren't installed to concentrate the electric field so that it discharges back into the air). So when you have a cloud that is charged one way and an airplane that is charged the other, there is the potential for a static discharge between them.
I think the charge of the aircraft is too small to have any effect on a lightning strike.
The plane just provides a lower resistance path than the air for the lightning bolt on its way from cloud to ground or cloud to cloud.
 

WBahn

Joined Mar 31, 2012
26,398
I think the charge of the aircraft is too small to have any effect on a lightning strike.
The plane just provides a lower resistance path than the air for the lightning bolt on its way from cloud to ground or cloud to cloud.
I would think that several thousand volts of static charge might just have an effect.

Let's consider the "low resistant path" hypothesis -- the lightning strike is normally going to be traversing many miles of very turbulent and heterogeneous air, typically with lots of precipitation all over the place. Does it really make sense that lowering the resistance of ten meters (small aircraft) or sixty meters (airliner) of that path is going to dictate where the entire channel is going to form?
 

Techno Tronix

Joined Jan 10, 2015
139
Airplane components made of ferromagnetic material may become strongly magnetized when subjected to lightning currents. Large current flowing from the lightning strike in the airplane structure can cause this magnetization.
 

crutschow

Joined Mar 14, 2008
27,908
I would think that several thousand volts of static charge might just have an effect.

Let's consider the "low resistant path" hypothesis -- the lightning strike is normally going to be traversing many miles of very turbulent and heterogeneous air, typically with lots of precipitation all over the place. Does it really make sense that lowering the resistance of ten meters (small aircraft) or sixty meters (airliner) of that path is going to dictate where the entire channel is going to form?
Not if the plane is not near the lightning leader path that's forming.
But it makes sense to me that if the plane is near where such a leader path is forming then the path will occur through the aircraft.
That's why lightning only occasionally strikes airplanes, not every time they are in the vicinity of a thunder storm.

Several thousand volts can generate a spark of no more than a few mm through air and I doubt is has a significant effect on a 100 million volt lightning bolt.
 

Thread Starter

sirch2

Joined Jan 21, 2013
1,029
Thanks guys, the second link provided by @bertus seems to suggest, as also suggested by several others above, that the aeroplane forms a path of least resistance and the lightening enters and exits the plane on it's way to the ground or a differently charged air-mass.

I guess it may also be the case that the plane, plus any charge it has built up, may actively induce lightening as it enters a region that is close to breakdown by being "the final straw".
 
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