Final answer:
Helicopters generally have two to six main rotor blades, which hold substantial rotational kinetic energy essential for their operation, as exemplified by the Auckland Westpac Rescue Helicopter Service's long history of rescue missions.
Step-by-step explanation:
Helicopters typically have between two and six main rotor blades. These blades are crucial for flight as they store a significant amount of rotational kinetic energy before takeoff and maintain it throughout the flight. Notably, helicopter engines aren't powerful enough to provide lift and significantly increase the rotational kinetic energy of the blades at the same time. An example of a helicopter in action is the Auckland Westpac Rescue Helicopter, which has been involved in over 50,000 life-saving operations since its inception in 1973, demonstrating the versatility and importance of helicopters in rescue missions.