Thanks to FO4Edit!
This mod adds 30 Damage Threshold (like in New Vegas) to Vertibirds. Any damage they take is reduced by 30, then Damage Resistance is applied. This effectively renders them immune to any weapon dealing less than 30 damage that doesn’t have Armour Piercing.
It doesn’t increase their Damage Resistance, so they’ll still die quickly to high damage weaponry like Missile Launchers- they’re just immune to potshots by raiders and synths with small arms.
Thanks to some neat work by Bethesda, NPCs will recognise if they can’t damage a target and will flee from it, so when a Vertibird flies over expect to see raiders running in panic as it scythes them down!
If you want this effect applied to power armour too, try Impervious Power Armour.
Both mods include a copy of Damage Threshold.esm. If you are using both, t is safe to override it on install.
If you would like to add this effect in your own mods, use the Damage Threshold resource.
This mod is compatible with Durable Vertibirds.