[Pseudoscience-is-malarkey (OP)]

Given how powerful lightning is, and how hard it is to know when or where it will strike, is it not really much of a direct threat to aircraft? Obviously avoiding lightning clouds is good practice, but it can't always be easy to do so, especially large, less nimble aircraft. I don't know.

[Bored chemist]

Most aircraft are built to survive being struck by lightning.

Edited to remove obvious typo.

[Pseudoscience-is-malarkey (OP)]

Most aircraft are built to survive being struck my lightning.

Given how powerful lightning is...

[alancalverd]

It's a common occurrence at intermediate altitudes (generally below 10,000 ft) and  can be a bit of a bugger but all the metal bits of the airframe are carefully bonded together so that the machine is effectively a Faraday cage with no potential difference between the parts. Radio and radar aerials that project through the shell are protected by discharge tubes or semiconductor shunts.

The real problem is the attendant turbulence, which can indeed destroy an airframe or distort it into an unflyable state, and violent "downbursts" of descending air and precipitation that can push you into the trees on approach (there's no excuse for taking off in a thunderstorm, but what goes up must come down). Rapid icing and hail damage in and around cumulonimbus should be survivable if it's not avoidable, but there are limits to what can be done or avoided by any particular aircraft, and no limits to what nature can throw at you.

I recall being struck twice on approach to Dublin. Lots of noise and shaking for a fraction of a second, but the real problem was landing on 2 inches of hailstones.

A friend got sucked into a cu-nim in a glider which rapidly disintegrated. He extricated himself from the still-rising wreckage and had the presence of mind not to open his parachute until he fell out of the cloud. He now wears a little gold caterpillar lapel badge, the emblem of parachute survivors. 

[paul cotter]

Metal box, no problem. What concerns me is composite construction techniques, commonly used in current aircraft. This product consists of a material which is essentially nonconducting at normal temperatures but will become a poor conductor at elevated temperature(due to decomposition) all covered in a thin metal film. If lightning hits a poor conductor the damage is usually extensive, eg a steel pole will at most suffer scorch marks while a tree will often burst open in flames. The engineers involved say "no problem" but they also said the same for the dc10 rear cargo door or the 737 max software. I'm not convinced, the energy dissipation in such a material could be catastrophic. 

[Bored chemist]

They are aware of the problem.
https://www.compositesworld.com/articles/lightning-strike-protection-strategies-for-composite-aircraft

[paul cotter]

Thanks for that article, bored chemist, it was interesting. I know they are aware of the dangers but I remain unconvinced. Because weight reduction is the main criterion for using composites the weight of conductive material added must be kept to a minimum. I suspect a sufficiently powerful hit will simply vaporise said metal film and then conduct through the composite with massive i²r heating. 

[Bored chemist]

When you say

weight reduction is the main criterion

Do you mean

Why is aircraft destruction via lightening extremely-extremely rare?

:-)

[evan_au]

Significant parts of airlines suffered severe damage after being struck by covid.

But what really takes them down is a lightning strike by baggage handlers... 

[alancalverd]

Why is aircraft destruction via lightening extremely-extremely rare?

The maxim of aircraft design has been ascribed to practically every pioneer from Henson (1838) to Rutan (1974): "Simplicate and add lightness." Nobody has ever managed to do so.

[Bored chemist]

Does a helium balloon design count as "adding lightness"?

[alancalverd]

Someone in my daughter's scout troop tried this. She tied some party balloons to her rucksack but found the additional drag when walking upwind was more disadvantageous than the overall weight reduction. But full marks for ingenuity and experimental guts. And a merit to the lad who offered to carry other people's light, bulky clothes in exchange for his cans of baked beans and corned beef.

The classic example was the R100/R101 airship saga: the later machine was overweight (yes, they even added an extra ballonet to lighten it!), crashed on its maiden voyage, and transferred its  reputation to airships in general, so the entirely satisfactory R100 was scrapped.

[SeanB]

Aircraft designers also know the parts most likely to be struck are pointy parts, like the top of the tail, the wing tips, the trailing edges of the engines, the nose and the rear stabiliser. Thus those parts, even those that move, do have rather substantial metal parts at the tips, and also have ground bonding flexible straps to bond them to the outer metal skin, and also the designers add in discharge brushes, rods of bare carbon fibre that will reduce charge build up and dissipate it, and thus reduce potential difference between the ambient and the aircraft, so reducing the chance of it being the cause for a discharge. The wheels also have the discharge brushes, and thus will shed charge as they get close to the ground, so there is no charge as the aircraft lands. Plus the same heavy flexible bonding straps, to conduct across the bearings so they do not suffer erosion from arc discharge.

Composite has the metal mesh embedded in it, or a foil of metal to act like charge spreader, and the large area means the unit current per square is low, plus brief, so the metal does not heat up much moving the charge across it. You might suffer damage, but it will survive. Of course you also do not fly into active storm cells, more due to the sudden steep air flow gradients being able to exceed the stress allowed on the airframe, there have been a good number of airframes written off for surviving flight through a storm cell, and the airframe exceeding it's maximum load limits multiple times, and the resultant stress deforming parts, so that, after landing safely, the airframe has been written off, because the number of failed rivets is uneconomical to repair.

[Deecart]

Most aircraft are built to survive being struck my lightning.

It is not your lighning, it also mine.

[Petrochemicals]

Someone in my daughter's scout troop tried this.

Aproximatley 1m3 can lift a kilo ish , I think that whomever dreamt it up must have their head in the clouds.

[Petrochemicals]

Probably for the same reason that powerline workers can work on the electrified  cables as long as they are not connected to the earth. I should think a lightning bolt would have  greater trouble passing  to an ungrounded plane and back again than continuing its path through the air surrounding the plane.

[alancalverd]

I think that whomever dreamt it up must have their head in the clouds.

Yes, that's one of the occasional joys of ballooning. But chilly.

[Bored chemist]

I should think

Indeed.

[Petrochemicals]

The charging of an aircraft seems to be a great factor in lightning strikes, .

jgrd55973-fig-0001-m.jpg (180.26 kB . 2128x1235 - viewed 2292 times)

A plane travelling through the air creates the obvious static, plus the fact that a plane is travelling through a magnetic field, that of earth.

[alancalverd]

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