The main rotor hub structure of the AH-54 was a very advanced example of titanium investment casting technology at the time.
Correction: Tough crowd. Sorry for the typo. Meant AH-56 and not AH-54.
Here is an interesting 2016 NASA report about CFD modeling and sub-scale tunnel testing of the
AH-56 rotor design:
http://hdl.handle.net/2060/20170000752