To get the Airship level 4 upgrade, you are going to need a lot of Truffle in Solarpunk. You can’t really find these on any of the islands because they are a byproduct resource. Here’s a quick guide to getting Truffle in Solarpunk.
Where to Get Truffle in Solarpunk
The main way to get Truffle is by setting up a pig farm. This requires the tier 6 upgrade at the Research Table, which unlocks the Pig Shelter research for 5x Carrot and 5x Wood. You can only obtain Carrots by unlocking the new islands upon reaching the Airship level 3 upgrade. That means you’ll have to finish all the following Traderbot trades to get this Airship level:
