Originally Posted by Deemar
I'm not quite sure why higher disk loadings are favoured for faster helicopters. I'm sure Nick Lappos has posted about it in the past. Maybe I'll check Stepniewski tonight.
Daniel, it's because a more powerful engine is already required for higher speeds. So there is less of a compromise in requiring more power for hover. If you take the power vs speed curve the higher disk loading has advantages at speed, due to less parasitic drag, so increasing disk loading just pushes the min power Vy to a higher speed. Ultimately retreating rotor stall limits how far you can push the effect though.
Like everything it's a compromise. It is probably why Nick commented about variable radius being all gravy, since you could increase the disk loading with speed and reduce it for hover. But mechanical complexity and poor transient performance limit its practicality.
Later thought: Increasing disc loading also reduces rotor mass (as you comment), but variable radius would still have you carrying around unecessary mass. This likely is another good reason why variable radius has never got beyond concept testing.
Dave, i'm amazed Leishman find's time to write all this stuff. Paper printed off for a quiet evening...