Originally Posted by Dave Jackson
One reason for having higher rotors outboard is to give the lifting surface (rotor disks) a dihedral and, hopefully, this dihedral will contribute to lateral stability.
Hmmm, don't forget this is a rotorcraft not a fixed wing. The cyclic is controlling the pitch/roll torque (ie acceleration) not velocity. The ONLY way to make cyclic control pitch/roll velocity, like a fixed wing, is to use gyro stabilisation. You favour electrohydraulic, i favour mechanical (partly because i have direct experience of how much of a headache hydraulics can be). Either way you need a gyro.
What you are proposing makes the machine more laterally stable if the pilot keeps the cyclic central. It does absolutely nothing for longitudinal stability, so you need the gyro anyway - assuming your objective was to reduce pilot workload. If you are going to fit a gyro, why compromise the packaging and aerodynamics? This is why i still favour outboard advancing intermeshing, with gyro stab. Even this is academic, since Sikorsky will soon set the counterrotating trend.
I have had fixed wing phugoid and spiral divergence demonstrated to me many times, and each time i have laughed at the design futility. If even a fixed wing cannot be absolutely stable, why bother compromising the aerodynamics? Next time you find yourself freighted in an Airbus or Boeing, watch the aileron/spoiler control surfaces fighting dutch roll. You will still get pilot induced oscillation anyway, since you can't damp the system. Northrop had to finally accept gyro stabilisation for the flying wing in the B2, and the helicopter is an even stronger case for not relying on aerodynamic stabilisation.
Why not just accept that rotorcraft suffer inherent instability, and design the control system to suit?
Mart