Definition
A hinge in a fully articulated helicopter rotor head that allows each blade to move forward and backward in the plane of rotation, independent of the other blades. This forward-and-backward motion is called lead-lag (or hunting) and accommodates the small changes in blade speed that occur as the blade flaps up and down during rotation.
Plain English
A pivot point on a helicopter rotor that lets each blade swing slightly forward or backward as it spins, rather than being locked rigidly in place.
Context Anchor
Seen in helicopter rotor system descriptions, especially when studying articulated rotor heads, blade movement, vibration, and rotor maintenance.
Derivation
Lead means to move ahead; lag means to fall behind. The hinge is named for the two directions the blade is allowed to move. The motion is also called hunting, because the blade appears to hunt forward and back around its average position.
Why Pilots Care
Reduces stress and vibration on rotor blades during forward flight, improving safety and component life.
Grounding Statement
Picture one rotor blade needing to give slightly forward and backward as it goes around, rather than being locked stiffly to the hub in every direction.
Intuition Check
Lead-lag does not mean the blade is leading or lagging the helicopter through the air. It means the blade is moving slightly forward or backward within the rotor’s own circular path.
Example Sentence 1
The lead-lag hinge lets each rotor blade adjust its position slightly as it travels around the rotor disc.
Example Sentence 2
During the daily inspection the mechanic verified free movement of all lead-lag hinges.