Zeeoo,
Supercritical aerofoils are justified for use on rotor systems, but as with everything else, the application of this technology to helicopters is very difficult. While we seek to exploit the benefits of the supercritical aerofoil's performance in the high speed high speed flow found on the advancing blade, we also need the aerofoil to have a high Cl_max capability for the retreating blade, which is not what supercritical aerofoils do best. Therefore, real helicopter aerofoils are a compromise between the type of supercritical aerofoils you might use on a fixed wing aircraft and the thicker, more cambered aerofoils you require for higher incidence operations at lower Mach numbers.
I can't comment on the aerofoils used on either blackhawk or apache as I am not familiar with the rotor systems. Perhaps Nick could help here.
In practise, designing a rotor system involves the careful integration of the characteristics of the aerofoils used along the rotor span and the rotor planform adopted. There are many ways in which the planform behaviour can be used to compensate for the limitations of given aerofoils. However, this is only really important when one is trying to squeeze out the maximum performance that contemporary technology will allow and it is certainly not something one would consider doing for a recreational aircraft as the cost and complexity of design, development and testing would far outweigh the benefits.
With regards the usefulness of 2D approximations of helicopter aerodynamics, I think you would be surprised! Although the rotor wake is actually highly unsteady and three-dimensional, this behaviour can very easily be broken down into the influence that it has on local 2D elemental aerodynamics. Indeed, this is what is done in every comprehensive analysis used by every manufacturer! This is perfectly acceptable for performance calculations and flight dynamics studies. The real limitations of the approach have been highlighted in vibration prediction. For this much higher order aerodynamic simulations are required and most people generally opt for three-dimensional computational fluid dynamics approaches here. The problem with this is that the run-time for the calculations, even on multi-processor supercomputers are huge; many weeks in fact. This of-coarse limits the usefulness of these powerful techniques to design verification rather than design synthesis.
Hope this helps
CRAN