Assertion: helicopter's rotor | /r/CapableOf | rotor two and four counterclockwise
Facets:
Source sentences:
text: If all rotors are spinning at the same angular velocity, with rotors one and three rotating clockwise and rotors two and four counterclockwise, the net aerodynamic torque, and hence the angular acceleration about the yaw axis, is exactly zero, which means there is no need for a tail rotor as on conventional helicopters.