tyler_larson writes "Just over a week ago, Jay Carter's CarterCopter managed to break a significant rotorcraft barrier, traveling at a mu ratio of 1. This 1-to-1 ratio (sometimes called the mu-1 barrier) represents a condition where the forward speed of the craft is the same as the speed of the tip of the rotor. This means that at a certain point, the tip of the retreating blade is "standing still" relative to the wind and producing no lift, while the rest of the blade is actually moving backwards through the air. Such a condition is normally impossible for a rotorcraft, and so the forward speed of a helicopter is limited by the the speed of the rotors. This accomplishment by the CarterCopter, which some insisted couldn't be done, proves that this new craft is not subject to that limitation."