How does flapping on the rotor blade of a helicopter work?

Question

How does flapping on the rotor blade of a helicopter work?

Answer 1

The first answer is best, and very thorough.  One thing it didn't mention is WHY the lead-lag is necessary.  Especially on longer rotor blades (UH1, CH-47) when you increase pitch, the blade will tend to bow "up".  When it does, the center of gravity changes slightly in reference to the rotor hub (just like a skater extending and retracting arms to control spin rate).  Well, as the up bowed rotor speeds up, the others are at their speed, so the rotor has to lead a little until the pitch comes down and it will adjust to center.  It's a little more complicated, but suffice it to say the helicopter rotor hub and hinge assembly is truly a marvel of engineering, and deserves intense study.

Answer 2

flapping is used to stabilize the rotor disc. once the blade flaps upwards, its pitch is reduced. this is achieved by fixed position of the control rod setting the pitch. as the blade moves upwards, the rod remains in the same adjustment, so the blade has to rotate downwards along the axial hinge. this reduces the pitch, which reduces the lift, which in return lets the blade drop again. if the blade drops below the rotor disc, opposite situation arises, with opposite inputs.

in the result implusive changes of position of blade are negated by this automated inputs, which in return stabilises the rotor disc and reduces vibrations.

Answer 3

The flapping hinge may be located at varying distances from the rotor hub, and there may be more than one hinge. The vertical hinge, called the lead-lag or drag hinge, allows the blade to move back and forth. This movement is called lead-lag, dragging, or hunting. Dampers are usually used to prevent excess back and forth movement around the drag hinge. The purpose of the drag hinge and dampers is to compensate for the acceleration and deceleration caused by Coriolis Effect. Each blade can also be feathered, that is, rotated around its spanwise axis. Feathering the blade means changing the pitch angle of the blade. By changing the pitch angle of the blades you can control the thrust and direction of the main rotor disc.

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