Two articles that cover this in depth are: 1. Revised Fold-Away Rotor Aircraft Concepts Emerge From Special Operations X-Plane Program. December 2024: https://www.twz.com/air/revised-fold-away-rotor-aircraft-con...
2. Bell’s Plan To Finally Realize A Rotorcraft That Flies Like A Jet But Hovers Like A Helicopter. September 2021: https://www.twz.com/41997/bells-plan-to-finally-realize-a-ro...
The second article covers decades of prior wind tunnel testing on the folding rotor concept.
https://en.wikipedia.org/wiki/Accidents_and_incidents_involv...
Id be interested in seeing a turboprop that can transition to a turbofan/jet once the prop is folded away. The f-35 was a step in this direction.