1 or 2 below?

I always see the first.
"Aeronautical experts will have to determine that," he added/ added he.
or
He added, "Aeronautical experts will have to determine that."

Sica"Aeronautical experts will have to determine that," he added/ added he.

added he is not very natural.

Really? I see it in novels a lot. Maybe in spoken language, people do not usually say it?

Sica I see it in novels a lot.

Are you reading modern novels by native speakers? If so, perhaps you could give us an example from one of them. There are no citations for "Direct speech," added he in the Corpus of Contemporary American English.

It's Harry Potter, Jed.
Here is an excerpt from the novel:
"Every year she makes us a sweater," said Ron, unwrapping his own, "and mine's always maroon."
"That's very nice of her," said Harry, trying the fudge, which was very tasty.
...
"There's a note!" said Ron suddenly. "A note fell out of it!"

These are not examples of 'added he', Sica.

We not infrequently use inversion in such situations with said and a noun or pronoun subject. We can even invert added with a noun subject. However, we do not invert many speech words when the subject is a pronoun.

Thanks!

We do ask people not to respond to questions unless they are sure of their facts, or have checked them.