Answer Happy

In a Helicopter, when you want to tilt the rotor plate, so that
the helicopter, in addition to obtaining lift, begins to move
forward, indicate -for a rotor composed of two blades- how these
should change their angle of attack, according to the position in
which they are, and all this is to ensure that the torque vector
generated by the gyroscopic effect of precession, points in the
correct direction.
a) The advancing blade should start to change its angle of
attack to negative when it is in the front, while the backward
blade should change its angle of attack to positive when it reaches
the back.
b) The advancing blade must start to change its angle of
attack to negative 90 degrees before reaching the front, while the
backward one must do the same but change its angle of attack to
positive, before reaching the rear.
c) The advancing blade must start to change its angle of
attack to positive 90 degrees before reaching the front, while the
backward one must do the same, to change its angle of attack to
negative before reaching the rear.
d) The advancing blade must begin to change its angle of
attack to negative 180 degrees before reaching the front, while the
backward one must begin to change its angle of attack to positive
90 degrees before reaching the rear.