Would it be possible to update this mod for 0.18? It seem to run fine by just bumping the version in info.json

I'd personally wait for this to be greenlit by the modmaker, after said modmaker hopefully verifies and thoroughly tests it...

But this is such a great mod I'll try your idea (thanks for your initial tests dude and reference to what to change, it really helps).

The easiest way to solve the problem with this mod is to comment line 31 in heli_gun.lua. I think recent updates have changed the sound sources and are causing the heli_gun_sound error. I did not look deeper, but I turned off the sound of the shot from the helicopter, and the mod works correctly. The only minus is the lack of shooting sound when shooting from helium. Sorry for my English. I am not fluent in this language: P
It need to change version to 0.18 in info.json too, of course :D

Thank you MariuszM94. This indeed helped and fixed my problem.

For 0.18, I can confirm this fixed the issue for me.
Just to clarify, for those like me that know enough to be dangerous...
In the Helicopter_0.3.14.zip, changed the \prototypes\items\heli_gun.lua file by commenting out line 31 with a double hypen. Then changed the \info.json file, line 6 to "factorio version:0.18".

Everything (except for that sound, which I assume from the earlier posts is an issue) seems to work, and now I can play with Helicopters in 0.18!!! Yea!!!
The only side effect I found is helicopters look like they pass underneath some objects such as inserters.
Would be nice to get this officially updated.

You can fix the heli_gun.lua file and keep the machine gun sounds. Insert this as the very first line:
local sounds = require("__base__.prototypes.entity.demo-sounds")

then change the sounds line to this:
sound = sounds.heavy_gunshot

This could break if they change how things are named again. And unfortunately I don't know how to fix the rendering issue (helicopter shown under wires and inserter arms.)

I've published a fork to this mod, and fixed the 0.18 compatibility issues, here:
https://mods.factorio.com/mod/HelicopterRevival

I hadn't looked into any other bug issues as of yet, though...