Thanks. Yes I do see that the retreating blade will suffer in this regard with a narrow tip airfoil in a tapered blade.
I was also reading up on the Boeing Hummingbird unmanned helicopter that you mentioned. Not much info has leaked, but it seems terribly interesting. For instance, they reduce blade RPM at different altitudes and different weights. And the endurance and performance figures for the 6-cylinder heli are nothing short of astounding! 2500nm range, ceiling of 30.000ft and 24h endurance - all very quiet, too. Amazing.
Has anyone experimented with reducing rotor RPM at altitude? I assume this could safely be done in any helicopter given enough height. It seems quite logical to do so, yet that's not part of the way heli's are operated - they run at constant RPM's all the time throughout.
I think Boeing are def on to something here - helicopters stress out components and are expensive to use simply because they're flown at the limit all the time. If there was a procedure to safely reduce rotor RPM and engine RPM at altitude, many benefits might be had, no? FW aircraft lean out and throttle back for long flights - who says heli's can't do the same?