Existing comment:
Modern Rotorcraft
Helicopter configurations have not changed significantly since the Vietnam War. Many models are modifications of decades-old airframes. However, notable innovations have occurred in engines, rotor systems, torque compensation, and noise reduction. Modern rotors with elastomeric bearings (flexible materials that can substitute for hinges) and flextures (flexible hubs) evolved out of earlier experiments with "rigid" rotors. They require less maintenance, reduce vibration, and are more responsive, allowing helicopters to perform maneuvers not previously possible. Shrouded tail rotors and the ducted-air NOTAR (No Tail Rotor) system have resulted in quieter and safer helicopters. |