Devil49,
Thanks for that info, it does seem to me the comments center around a yaw control that is both powerful and sensitive, and that we are talking about a bit of Pilot Induced Oscillation - PIO. Not much, I'll bet, and easily compensated for.
The reason why it gets worse as the aircraft descends is probably little to do with flow and such, and lots to do with the pilot getting tighter on the controls as the ground nears.
The reason why I asked about the frequency of the wiggle is that the airflow around the machine cannot generate a 2 or 3 Hz problem, because the aerodynamics are slower than that, but the pedals surely can. NOTARs are a bit slow on the yaw response, for example, and they captiolize on that aerodynamic force.
Generally the PIO can be fixed with a bit of damping on the pedals - like a door closer, a small hydraulic cylinder is imposed that makes the pedals hard to move too fast, but easy to move slowly.
Even a Huey is sensitive in the pedals, and likely to get a tad squirley when a pilot dances a bit too much on the pedals.
JNo,
Yes, I agree the right drift is exactly why the skid is low. The tail rotor is producing a force, (all US convention hereon) that pushes the helo to the right, a factor called "translating tendency". When the pilot corrects the right drift, he automatically rolls the aircraft a it to the left. When everything is settled, the roll attitude is about 2 to 3 degrees to the left, so the main rotor thrust is tilted a bit to the left to counter the tail rotor thrust to the right. 3 degrees tilt equals 5% of the main rotor thrust.
There is a hard to kill belief that the height of the tail rotor makes this worse, as if the comparison between the tail rotor hub and the main rotor hub height is somehow a part of the aerodynamics. Sadly, this one will not quite go away! Actually, the higher the tail rotor, the LESS the hover bank angle is!
Those who fly S-76 note about 2 to 3 degrees, those who fly a center line tail rotor (A-109 and any fenestron bird, for example) can you tell us what you see on the roll gyro when in a steady hover, no wind? I predict about 5 degrees or so. Comanche leaned at 5 degrees with its centerline fantail.