Here's a pic of their blades layout:
http://batman.mech.ubc.ca/~hph/thunderbirddesign.gif
(note the blade rotation arrows)

What I'm wondering about the blades:
- Why the odd taper? I'm guessing the taper alleviates tip losses,
but why does it begin at the ~.6 span mark? I'd expect taper across the
entire blade for the best inflow results, but then again I'm a non-expert.
- Why no twist? Does the taper alone sufficiently linearize the
inflow?

I'd be grateful for any thoughts on these questions, and I know that
probably no one in this newsgroup has an exact answer. I'm just a
student studying helicopter aerodynamics and am interested in the UBC
HPH design.

Here are some of their CFD visualizations if it helps anyone analyze:
http://batman.mech.ubc.ca/~hph/projects/cfd.html

And here's some info on another HPH design, with blades that are more
conventional (to my knowledge at least):
http://www.calpoly.edu/~wpatters/davi.jpg



Hope someone here knows more about this than I do,
jc