Turns are made in a helicopter, as in an airplane, by banking. In forward flight, the rotor disc is tilted forward which also tilts the total lift-thrust force of the rotor disc forward. This total force is the resultant of a vertical component, lift, and a horizontal component, thrust, acting forward. When the helicopter is placed in a bank, the rotor disc is tilted sideward. This causes the lift component to be tilted sideward, which in turn, is divided into two components--one acting vertically that opposes weight, the other acting horizontally to the side and opposes centrifugal force (fig. 24). It is this horizontal component of lift that pulls the helicopter in the direction of bank and thus causes it to turn. Briefly then, we can say that a turn is produced by banking the helicopter, thus allowing the lift of the rotor disc to pull the helicopter from its straight course.
As the angle of bank increases, the total lift force is tilted more toward the horizontal, thus causing the rate of turn to increase because more lift is acting horizontally. Since the resultant lifting force acts more horizontally, the effect of lift acting vertically (vertical component) is decreased (fig. 25). To compensate for this decreased vertical lift, the angle of attack of the rotor blades must be increased in order to maintain altitude. The steeper the angle of bank, the greater the angle of attack of the rotor blades required to maintain altitude. Thus, with an increase in bank and a greater angle of attack, the resultant lifting force will be increased and the rate of turn will be faster.