Final answer:
If the lift imbalance caused by the advancing and retreating blades of a helicopter's rotor disk is not corrected, it could make the helicopter experience instability and roll, known as dissymmetry of lift. Helicopters rely on stored rotational kinetic energy to maintain lift due to limited engine power. Counter-rotating blades help cancel out torque and stabilize the helicopter.
Step-by-step explanation:
If left uncorrected, greater lift produced by the advancing side of the rotor disk compared to the lift created by the disk's retreating side could make the helicopter experience a phenomenon known as dissymmetry of lift. This could cause the helicopter to roll and become unstable. To counteract this, helicopters are equipped with mechanisms such as blade flapping and cyclic pitch control that help to balance the lift across the rotor disk. Additionally, helicopters store high amounts of rotational kinetic energy in their blades, which is provided before takeoff and maintained until the end of the flight. This energy is critical for maintaining lift, because helicopter engines do not have enough power to both lift the helicopter and significantly increase the blades' rotational energy mid-flight. Moreover, having two sets of lifting blades rotate in opposite directions (counter-rotating rotors), which eliminates the need for a tail rotor, is beneficial because it cancels out the torque produced by each set of blades, thereby maintaining the helicopter's stability.