Helicopter Performance, Rotor Interaction, Azimuth Angle

The main components that play the most crucial roles in a helicopter are the main rotor and the tail rotor. The main rotor generates lift, while the tail rotor primarily controls the rotation. Today, let's explore the interaction between the main rotor and the tail rotor and summarize methods to enhance performance.

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Interaction between the Main Rotor and the Tail Rotor

The main rotor and the tail rotor are positioned close to each other, resulting in mutual influence from the airflow. When they rotate, a swirling airflow called wake is generated at the blade tips. This wake creates turbulent airflow and affects the performance of nearby rotors.

Areas Most Affected

The main rotor and the tail rotor are located at the front and rear of the helicopter, respectively, with the closest interaction occurring when the main rotor is rotating.

azimuth angle

Considering the main rotor as the reference, the point closest to the tail rotor is defined as 0°, and the furthest point is 180°. This angle is called the azimuth angle, denoted as ψ.

Differences in Tail Rotor Performance

When the tail rotor is affected by the main rotor's rotation, the torque value increases. Torque represents the force required to rotate, multiplied by the distance. Therefore, an increase in torque demands more energy for rotation, resulting in decreased performance.

canted helicopter

Cant Angle

The tail rotor is often tilted at around 20°, as shown in the picture. This angle is known as the cant angle. Tilting the tail rotor slightly offsets the flow of the tail rotor towards the front of the main rotor, reducing their interaction.

 

In helicopters, the main rotor and the tail rotor are positioned closely, causing mutual influence from the rotational wake, which decreases performance. To address this, various studies are being conducted, including repositioning the tail rotor and changing the direction of rotation.