In forward horizontal flight, how does the angle of attack of the advancing rotor blade compare to the retreating blade?

In forward horizontal flight, the angle of attack of the advancing rotor blade is indeed less than that of the retreating blade. This phenomenon occurs due to the rotational dynamics of the rotor system. As the helicopter moves forward, the advancing blade moves into the oncoming relative wind, which increases the speed at that point, effectively decreasing the angle of attack required to maintain lift.

Conversely, the retreating blade experiences a decrease in effective airspeed as it moves away from the direction of flight. Because the rotor blades are experiencing different airspeeds (higher for the advancing blade and lower for the retreating blade), the angle of attack must be adjusted accordingly.

In essence, the retreating blade needs a higher angle of attack to compensate for the reduced airflow while still generating sufficient lift, whereas the advancing blade has a more favorable flow situation and requires a lower angle of attack. This relationship is crucial in understanding lift dynamics and rotorcraft performance during forward flight.