Cyclic Cross-Coupling

What it is

Give a hard pitch input and the helicopter also rolls a little. The frame, heavy around the pitch axis, lags behind the rotor disc; the difference loads the rotor, and through gyroscopic precession that load comes out as a roll. You can see it:

• at the stops of tic-tocs, as the centre of the rotor rotating a little;
• in a hover, by shaking the elevator stick back and forth -- the helicopter tilts in roll and drifts in yaw.

Cyclic cross-coupling compensation feeds a little of the pitch command (how fast it's changing) into roll, so the two effects cancel.

Settings

On the Profiles tab:

Setting	Default
Cyclic Cross-Coupling	on	Enables it.
Cross-Coupling Gain	50	Strength of the pitch-to-roll compensation.
Cross-Coupling Ratio [%]	0	Adds the opposite (roll-to-pitch) compensation, as a percentage of the pitch-to-roll.
Cross-Coupling Cutoff [Hz]	2.5	How fast the compensation acts.

Tuning

Tune this early, while the gains are still soft and the coupling is easy to see.

1. Hover and shake the elevator stick, or fly tic-tocs.
2. If the helicopter rolls, raise the gain in small steps until the roll is gone, or until raising it stops making a difference.
3. Check with piro-flips: cross-coupling compensation changes how the helicopter responds at different points of the piro-flip, so increase it gradually to get used to the feel.

Stiffer main rotor dampers usually need less gain.

Constant cross-coupling

Very hard dampers, a very low headspeed or some head designs can leave the blades' flapping hinge off-centre. Then the coupling is constant rather than only during pitch changes. The ratio setting can help with that.