Does the direction in which a helicopter’s main rotor turns—clockwise or counterclockwise—matter? Let’s explain.
A helicopter is a rotary-wing aircraft where both lift and thrust are provided by the rotation of one or more rotors. The helicopter takes off with the help of a large-diameter rotor located on the roof, called the main rotor. The rotor is always positioned parallel to the ground, and its blades are set at an angle to the plane of rotation. This angle can vary widely, from zero to 30 degrees. The higher the angle, the more lift the rotor generates as it spins.
Types of Helicopter Rotor Configurations
Classic Configuration This is the simplest and most common design, with only one main rotor. When the rotor spins, it creates a reactive torque that causes the helicopter’s body to rotate in the opposite direction.
To counteract this, a tail rotor is usually employed, often found on the tail boom or inside a circular shroud. When the helicopter flies forward and the main rotor turns clockwise, for example, the oncoming airflow exerts a stronger force on the blades on the left side, increasing their efficiency.
As a result, the left half of the rotor creates more lift than the right half, producing a rolling moment. To counteract this, an automatic swashplate system is used to decrease the blade angle on the left side and increase it on the right, equalizing the lift across the rotor.
Twin-Rotor Configuration In this case, the helicopter is lifted by two rotors located on the same axis. The reactive torques from these rotors cancel each other out due to synchronous and opposite rotation. Their planes of rotation may have varying degrees of overlap if the number of blades is less than four.
Longitudinal Configuration This design also uses two horizontal rotors, but they are positioned one behind the other and rotate in opposite directions. The rear rotor is elevated above the front rotor to reduce the negative impact of its downwash. This configuration is mainly used in heavy-lift helicopters.
In Which Direction Does a Single Helicopter Rotor Turn?
So, for helicopters with two rotors: they rotate in opposite directions. But what about a single rotor? It turns out there is no set rule; it all depends on the design specifics and, to some extent, tradition.
For example, on French helicopters, the main rotor turns clockwise, while on British, American, Italian, and German helicopters, it turns counterclockwise. However, from an aerodynamic standpoint, both options are equally valid.