The unloaded-rotor concept, which was used in the Fairey Rotordyne, is currently being reapplied in the Carter Copter,
the Piasecki Vectored Thrust Ducted Propeller and
Boeing Canard Rotor/Wing X-50A. I believe that this compound configuration of rotor plus wing will never prove to be viable product. The wings represent an undesirable weight and thrust obstruction in hover, while the rotor represents an undesirable weight and drag during forward flight.
IMHO, today's high strength, lightweight materials combined with advanced electrostrictive actuators will allow the wings and the rotor(s) of the compound configuration to be united. The result of this union will be a pair of laterally displaced and significantly advanced rotors.
Nick brings up the valid argument about
" The problem is ... maintaining commercial viability. Fuel flow, payload, parts count all count in the real equation." This is where the three lateral rotor configurations should 'shine'. The Side-by-side, the Interleaved and the Intermeshing offer various pros and cons visa-vie each other, however, as a group, they offer a number of significant advantages.
During hover and other slow flight requirements they should outperform all other alternatives, and particularly the V-22 tiltrotor.
In fast forward flight, they may not quite match the cruise speed of the tiltrotor. However, these three configurations can have propellers that are optimized for forward flight, whereas the V-22 proprotors are a compromise between a propeller and a rotor. In addition, these three configurations can substitute turbofans with PTOs for even faster forward speeds, which the tiltrotor cannot do.
Sikorsky's
Advancing Blade Concept combined with
Active Blade Twist should make this all come true.