Assertion: helicopter's blade | /r/AtLocation | a rotor hub
Facets:
value: by horizontal flapping hinges
type: MANNER
Source sentences:
text: Because the blades are attached to a rotor hub by horizontal flapping hinges, which permit their movement in a vertical plane, the advancing blade flaps up, decreasing its angle of attack, while the retreating blade flaps down, increasing its angle of attack.