Low tip Mach number stall characteristics and high tip Mach number compressibility effects on a helicopter rotor having an NACA 0009 tip airfoil section

Robert D. Powell, Jr., Paul J. Carpenter
naca-tn-4355
Jul 1958

An investigation has been conducted on the Langley helicopter test tower to determine experimentally the low tip Mach number stall and high tip Mach number drag divergence characteristics of a helicopter rotor having an NACA 0009 tip airfoil sections, which tapered to an NACA 0017 root airfoil section and had -5.4 degrees of twist.

An Adobe Acrobat (PDF) file of the entire report:
http://naca.central.cranfield.ac.uk/reports/1958/naca-tn-4355.pdf