What control inputs are required to perform a "turning-while-in-flight" maneuver in a helicopter?

Question

My question is relatively simple and has to do with the required control inputs to perform a simple turning maneuver over a large area.

Suppose a helicopter is traveling in forward flight, straight and level, and the pilot has to alter course to circle a large area. Now, suppose the helicopter begins a slight rightward turn, while continuing to fly 'forward', and ends up semi-circling over a broad area.

I want to make the point that the helicopter is not yawing/turning on its own axis, but rather performing a turn over a large area.

The resulting flight path, if viewed from above, would essentially be a semi-circle or horseshoe shape.

This would obviously involve some rightward banking. What I want to know is this: can this maneuver be performed with only cyclic inputs, or would there also have to be pedal inputs to complete such a turn? And if it can be performed only with cyclic inputs, what exactly would those inputs be apart from rightward cyclic? Thanks in advance!

Answer 1

Yes it's cyclic inputs only for banked turns because there is no adverse yaw due to ailerons to compensate for. You will be working the pedals to keep the ball centered, but this is only in reaction to torque changes from increases in rotor pitch and power demands.

Note that the airplane isn't using rudder to turn either; only to correct for adverse yaw. What brings the nose around in the turn is the vertical fin. The banked wings creates a lateral force vector, moving the airplane sideways as it goes forward. The sideway motion cause the airstream to strike the vertical fin from the side, and the airplane's inherent weathervaning tendency brings the nose around to keep it aligned with the arc of a turn. If an airplane had no adverse yaw at all, you would not need to use any rudder to help with turns.

A helicopter is the same. There is a small fin back there that gives it modest weathervaning tendency (the disk area of the tail rotor also contributes). The pedals are just there to change tail rotor pitch to adjust for off-axis yawing motions induced by torque changes (which can be in either direction, depending on whether torque is going up or down); just as on the airplane the pedals are just there to compensate for adverse yaw due to aileron displacement. If the helicopter had some automated system to always compensate for torque changes, you would not need to touch the pedals to turn.

In practical terms, in both cases, when flying you simply do whatever you have to do with your feet to keep the skid ball centered; in the airplane you are generally reacting to aileron movements, and in the helicopter to torque/pitch changes. The power plane pilot learning helicopters has to adjust to get out of the habit of squeezing a little into-turn rudder to anticipate adverse yaw, and has to instead anticipate the subtle yaw changes - in either direction - from the power and pitch changes the pilot may input during the turn.

Answer 2

As usual in a helicopter, you typically need to adjust all controls because everything is cross-coupled.

The primary input to initiate a turn is lateral cyclic. This banks the helicopter and tilts the lift vector so that a centripetal force is formed. The pedals are only used to make small corrections and keep the helicopter aligned with the incoming airflow. Usually a yaw string attached to the outside of the cockpit window shows whether the helicopter is in a skid, slid or coordinated turn.

Since the lift vector is tilted due to the banking, additional lift will be needed to maintain altitude. For this, collective and throttle are increased. Again, this has an effect on the torque, so the pedals are needed to keep the nose pointed into the airflow.

For steep turns, forward cyclic may be required to keep the airspeed from dropping.

From the FAA Helicopter Flying Handbook, chapter 9:

How fast the helicopter banks depends on how much lateral cyclic pressure is applied. How far the helicopter banks (the steepness of the bank) depends on how long the cyclic is displaced. After establishing the proper bank angle, return the cyclic toward the neutral position. When the bank is established, returning the cyclic to neutral (or holding it inclined relative to the horizon) will maintain the helicopter at that bank angle. Increase the collective and throttle to maintain altitude and rpm. As the torque increases, increase the proper antitorque pedal pressure to maintain longitudinal trim. Depending on the degree of bank, additional forward cyclic pressure may be required to maintain airspeed