Just to throw two (hopefully relevant) ideas into this very interesting discussion.
The CH-47D has rotor blades that are significantly wider chord than the predecessor's - nearly 50% more chord. Being made of fiberglass, the area behind the spar was quite rough, certainly in comparison to the surface of the metal blades. I asked about the roughness, and was told it was actually beneficial for keeping flow attached.
Second point - I noticed on the tips of the Bell 212 blades recently that there was the 'normal' erosion on the leading edges, and also an area of erosion on the trailing edge near the tip - there appeared to be quite a large area between the two with no erosion, which indicated to this uneducated eye that perhaps there was quite a bit of flow separation going on here.
Saw the same things on the tail rotor blades of a Hughes 500 - leading edge erosion with a gap and then sand-blasting at the (reflexed) trailing edge.
Any comments?
And has anyone actually tried turbulator tape on a helicopter rotor blade?