I think CB has a good story below to explain a decreasing tilt to the right. (which is what Birdy describes)
It doesn't however address the original issue of the
difference in roll effect between the shorter and longer rotors..
and that may be as simple as
any difference in the individual symmetry of the two different sets - be it twist (as Juergen suggests), weight, profile etc. But if it is a consistent issue it is worth thinking about a bit more, just out of interest.
But some more info would be good if you have it Birdy?,
1. What are the roll characteristics of the shorter set at each of the speeds listed above?
2. And at 0 AS, what is the cause of the roll to the right (at idle? - lack of airflow trim? .. is there some rotor head trim built in)
3. And to what extent does that occur with the shorter blades.
I don't see what the pre-rotator cable could do, other than add friction.
CB's explanation below of the effect of coning is intriguing - as we have an 'imperfection' (coning, due to the flex of the rotors
edit - builtin?) to some extent cancelling the tendency of the rotor disk (if it was on a flat plane) to lean left (very neat really!) I don't know why he didn't say that on the first page, Birdy (he does in a way in post #22, and so does JC in #26, but not so clear!) maybe our stumbling around in the dark helped!
(Or maybe he just thought we would not understand it at that stage)
Quote CB (RTV thread post #11)
Because of coning, the blade in front, the 12 o’clock blade, catches a bit more wind than does the 6 o’clock blade. There are other reasons as mentioned by JC but that’s even more complex.
Now you already know that on a rotor with central flap hinges, displacement lags force by 90º. It shouldn’t be much of a stretch to understand that if a blade takes an upward whack at 12 o’clock, maximum upward travel occurs 90º later, at 9 o’clock.
As you also know, cyclic flapping relative to the spindle axis equals cyclic feathering relative to the tip plane axis. That’s what equalizes lift between 12 o’clock and 6 o’clock blades.
The bottom line is that a coned rotor tilts a bit to the right, depending upon coning angle and airspeed so to go straight, you must hold a tad of left stick pressure.
JC’s point was that airflow through the rotor disc is not uniform; more air flowing through the front half of the disc than the rear half, also contributing to the leftward tilt. That effect is more pronounced at low speed, as speed increases, flow through the disc becomes more uniform.