Definition
A main rotor system that turns counterclockwise when viewed from above the helicopter. This rotation direction is standard on most U.S.-built helicopters and determines the direction of torque reaction on the fuselage, the side on which translating tendency acts, and the pedal inputs required to counter yaw.
Plain English
The big rotor on top of the helicopter spins to the left when you look down at it from above. Most American helicopters are built this way, and it affects how the aircraft wants to twist and drift, which the pilot has to correct for.
Context Anchor
Seen in helicopter instrument flying and power-control discussions, especially when explaining why a power change can also require pedal correction.
Derivation
Counterclockwise' means the opposite direction to the hands of a clock. Clocks were the everyday reference for rotation direction long before aviation, so the term simply borrows that visual: imagine looking down at a clock face and the hands running backward.
Why Pilots Care
Determines the direction of fuselage yaw when power is changed, requiring specific pedal inputs to maintain heading.
Grounding Statement
Picture looking straight down at the rotor hub: if the blade tips move around like a clock running backward, the main rotor rotation is counterclockwise.
Intuition Check
Do not judge counterclockwise main rotor blade rotation from the side or from underneath the helicopter. In this context, it means the direction seen when viewing the rotor from above.
Example Sentence 1
Because the Robinson R44 has counterclockwise main rotor blade rotation, the pilot applies left pedal to counter the resulting right-yaw tendency in a hover.
Example Sentence 2
The pilot monitored power changes carefully, knowing the counterclockwise main rotor blade rotation would produce a right yaw that needed immediate correction.