Hi Dave,
"Blade element theory and common logic will do."
Agreed. These days you would go straight from blade element calcs to CFD. Building a ground rig will be a good way to avoid some of those ScArY licencing costs though.
"I strongly believe ... that the Intermeshing configuration is the best configuration for small rotorcraft..."
I strongly believe that you are right!
"...the Interleaving configuration may be the best for large transport rotorcraft ..."
Agreed. The additional payload justifies the additional drivetrain complexity. I get puzzled sometimes since the questions are not in the context of a specific project, so i am not always sure where the discussion is going.
"(Tri-teetering hub) ... undersling may eliminated the need for lead/lag hinges."
OK. Need to be proven/optimised on a ground rig, for perfect blade hub stiffness match.
"...large flapping hinge offset will allow for a smaller obliquity ..."
This is heading towards a rigid hub though. I can't help but wonder if a hysteric elastomer lead-lag bush would work as well. Again, though, it just needs proving out on a ground rig.
"... S-69 (XH-59) ABC coaxial had quite rigid 3-blade rotors ... high vibrations. ... X2 coaxial series shows 4-blade rotors."
Again, i wonder about the use of elastomeric lead-lag bushes to avoid coriolis induced vibration. Don't forget 4 bladed rotor will introduce (potentially avoidable) profile drag, over 3 bladed rotors.
Mart
[Edit: Ammendment]