JNTU B.Tech IV HELICOPTER ENGINEERING Previous Question Paper (July - 2021 - R16)

The genealogical tree of a helicopter traces the evolution of vertical flight from early concepts to modern configurations. The primary classifications include:

1. Single Main Rotor with Tail Rotor: The most common configuration where a large horizontal rotor provides lift and thrust, while a small vertical tail rotor counteracts the torque produced by the main rotor.
2. Tandem Rotor: Features two large rotors mounted one behind the other. The rotors rotate in opposite directions to cancel out torque, eliminating the need for a tail rotor.
3. Coaxial Rotor: Two rotors mounted on the same mast, one above the other, rotating in opposite directions. This design is highly compact and provides excellent hover stability.
4. Intermeshing Rotor (Synchropter): Two rotors mounted on masts angled toward each other. The blades intermesh like gears, rotating in opposite directions to cancel torque.
5. Tip-Jet Driven: A design where small jets or rockets are mounted at the blade tips to drive the rotor, eliminating the need for a complex transmission system.

A helicopter gains height by increasing the total lift force produced by the main rotor system until it exceeds the weight of the aircraft. This is primarily achieved through the collective pitch control, which increases the angle of attack of all rotor blades simultaneously.

The aerodynamics of a climb involve the following principles:

1. Collective Pitch Increase: When the pilot raises the collective lever, the pitch angle of all blades increases. This increases the lift coefficient, resulting in a higher vertical force component.
2. Thrust-to-Weight Ratio: For a vertical climb, the rotor thrust must exceed the sum of the helicopter's weight and the induced drag.
3. Induced Flow: During a climb, the air is drawn downward through the rotor disk. The velocity of this induced flow changes compared to a hover, which affects the effective angle of attack of the blades.
4. Power Requirements: Climbing requires a significant increase in engine power to overcome the additional induced drag created by the higher lift production. The engine must maintain constant rotor RPM despite the increased aerodynamic load.

Where T is thrust, W is weight, D_i is induced drag, and m(dV/dt) represents the acceleration component during the climb.