Another speculative thread, for technical debate...
Recent discussions with Dave Jackson have brought up some interesting issues. Nobody will dispute the advantages of counterrotation to avoid retreating blade stall in high speed flight, but the planform is the subject of much debate.
My belief is that, after weight, the single biggest constraint to helicopter operation is aircraft width. For a given disk loading coaxial suffers from weight over designs with laterally seperated rotors, but allows a very compact design. This leads to the next question: What about longitudinally seperated rotors?
The
CH-47 Chinook has 3 bladed rotors and an effective hinge offset of 6.3%, but is limited in speed by vibration. For a smaller design, what if the rotor system was replaced by Comanche style rotors with 4 blades and an effective hinge offset of 15%? This design minimises the disk loading for a given width, while maintaining a relatively compact aircraft. The longer fuselage perhaps limits it to transport applications, although interleaving is feasible.
In high speed flight the fuselage would suffer torsion as the retreating blades were unloaded. In principle it could achieve the same speeds as X2 using seperate propellers. The front rotor could have a lower disk loading to ensure VRS required nose-down recovery before rear rotor entered VRS. The only downside i can see is the increased complexity of a distributed powertrain, needing to be fatigue proofed at full power. An upside would be easy packaging of the twin swashplates which will eventually allow variable blade twist in different flight conditions.
Any merit, or have i completely lost the plot?
Mart