JNTU B.Tech III FLIGHT MECHANICS II Previous Question Paper (October - 2020 - R13)

Aerodynamic autorotation in forward flight occurs when a helicopter's rotor system is driven entirely by the upward flow of air through the disc, rather than by the engine. In forward flight, the rotor disc is tilted forward, and the aircraft descends at a specific glide angle. The rotor disc is divided into three distinct regions: the driven region (outer), the driving region (middle), and the stall region (inner).

In the driving region, the resultant aerodynamic force vector is tilted forward of the axis of rotation, providing the necessary torque to overcome drag and maintain rotor RPM. In the driven region, the force vector is tilted backward, acting as a brake. The balance between these regions maintains a steady state of rotation. The pilot must manage the collective pitch to control the rate of descent and the rotor RPM, ensuring the rotor remains within operational limits during the glide.

To ensure controlled flight, the pilot utilizes four primary controls: the cyclic, collective, anti-torque pedals, and the throttle. The cyclic controls the tilt of the rotor disc to manage pitch and roll, while the collective adjusts the pitch of all blades simultaneously to control vertical thrust. The anti-torque pedals manage the yaw by adjusting the tail rotor pitch, and the throttle maintains engine power.

The pilot's task involves continuous integration of these controls to meet mission profiles such as hover, transition, cruise, and descent. This requires monitoring flight instruments for airspeed, altitude, and rotor RPM, while making constant, coordinated inputs to compensate for aerodynamic coupling, such as the tendency of the aircraft to yaw when collective is increased. The pilot must anticipate changes in flight conditions, manage power settings for fuel efficiency, and maintain aircraft stability within the structural and performance envelopes defined by the mission requirements.