I'm trying to use the custom aircraft icons from the GitHub, I've extracted them to 

C:\Users\danie\AppData\Roaming\ABarthel

but I can't get them to show up. All the Online Vatsim aircraft still look like Cessna's, when I would like them to look more like jets (or ideally a mix of both)

Am I doing something wrong? Any help would be appreciated

LNM uses the GA aircraft icon for all VATSIM aircraft because there is no information if it's a jet or not.

It might work if an online tool flying tool injects the right aircraft into the simulator but this can result in duplicate aircraft on the map (LNM tries to resolve this but it does not always work).  See here: https://www.littlenavmap.org/manuals/littlenavmap/release/latest/en/ONLINENETWORKS.html

Alex

Ahhh ok, thanks. I wasted so much time on trying to get this working haha! Is it possible to just change the default icon?

Yes but there are several ones. You can just copy all jet icons
aircraft_jet.svg,
aircraft_jet_ground.svg,
aircraft_jet_ground_online.svg,
aircraft_jet_ground_user.svg,
aircraft_jet_online.svg and
aircraft_jet_user.svg
over the respective plain aircraft icons
aircraft_small.svg,
aircraft_small_ground.svg,
aircraft_small_ground_online.svg,
aircraft_small_ground_user.svg,
aircraft_small_online.svg and
aircraft_small_user.svg . 

Then all traffic is shown as jet.

Alex