FAA type designator document
https://www.faa.gov/documentLibrary/...tors_FINAL.pdf
does not include designators for FX or EX types.

My FX-3 ADS-B out does not include a type designator and, although I call myself "experimental Cub", I am often asked for my aircraft type. Perhaps that's because I'm sometimes going a bit faster than a J3 would, or maybe it's because a J3 would not usually have ADS-B out capability.

Has CubCrafters reached any agreement with FAA on an appropriate type designator for the FX-3? Wasn't Jon Delamarter working on this before he left?

How do other FX-3 owners identify their aircraft type when talking to approach or center?