Rotor Configuration

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Rotor Configuration

When the engine developed enough power to lift the helicopter, the main problem was how to counter the main rotor forcing the fuselage to rotate in the opposite direction of the rotor.
This effect is known as Torque.

The classic solution was a small tail rotor to push the fuselage in the opposite direction of the torque force.

Another popular solution were tandem rotors. The primary advantage of this configuration is the ability to lift heavy loads whose position relative to the helicopter's centre of gravity is less critical than in the single rotor configuration.
Because there is no anti-torque rotor, full engine power can be applied to lifting the load. Disadvantages of the tandem rotor system are a complex transmission and more drag due to its shape and excessive weight.

And coaxial rotors, in which the goal is obtain a notably compact design. Being the fuselage independent of the lifting system dynamics permits the design to be strictly functional as related to the helicopter mission.

After the torque effect, the other main problem was the tendency of the helicopter to roll laterally in the direction of the retreating rotor blades as the advancing blades pass through denser air and generated greater lift than the retreating blades that pass through less dense air.

This problem was eventually solved by the introduction of a flapping hinge in the rotor head, which allowed the advancing blade to climb slightly, thereby reducing its angle of attack and the amount of lift generated, while the retreating blade fell slightly, thereby increasing is angle of attack and the amount of lift generated.

NOTAR A relative new solution, the NO TAil Rotor, uses jet thrust rather than blades to provide directional stability and reduce noise, providing the world's quietest helicopters.

NOTAR also utilizes Coanda Effect with the rotor downwash across the tailboom and an internal airflow through the tailboom to produce a sideways "lift", or more correctly "thrust" to counter main rotor torque.

The jet thrust from the nozzle at the end of the tailboom is primarily used for directional control, with a very small contribution to anti-torque force.

List of Rotor Configurations Types

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User Contributed Notes

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mike jones ( seattle wa usa )
You have it a little backwards. Disymetry of lift is offset by the advancing blade staying relatively flat (flat pitch) while the retreating blade climbs, (increasing angle of attack) thus reducing lift on that side of the rotor disk. forward speed is thus limited to stall speed on retreating blade. Retreating blade stall sets limits on forward speed on all pure helicopters. Mike, 28 year Chinook pilot.

daniel ( miami fl usa )
Actually he was right the first time. If the flapping hinge were not there, the advancing blade would be at the same angle of attack as the retreating blade, but the advancing blade has more incoming airflow therefore produces more lift. The flapping hinge allows the advancing blade to flap upward therefore reducing its angle of attack which reduces its net lift. The retreating blade doesn\'t produce very much lift so it flaps downward which increases its angle of attack therefore increasing its net lift.

dave sullivan ( yeovil somerset united kingdom )
Sorry 28 yr old chinook pilot, the others are right. Look back at your theory of helicopter flight class notes.

james grenfell ( brisbane qld australia )
Guys, I am not able to piece your comments together here. I am new to Heli\'s but believe I have a strong knowledge of fixed wing machines. If an advancing blade flaps up this would increase in AOA? Retreating blade down will decrease AOA? A flapping hinge should maintain lift for the advancing blade and increase AOA and lift for retreating blade to negate roll in the direction of the retreating blade. If someone can clear this up i would be greatfull.

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