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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!

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    $\begingroup$ Perhaps you mean a coordinated turn? $\endgroup$ – mongo May 17 at 15:02
  • $\begingroup$ I don't quite understand your description. Suppose that, at the beginning of the maneuver, the nose of the helicopter is pointing north. After it flies a semicircle, is the nose still pointing north (meaning that for the last part of the maneuver, it's flying backwards instead of forwards), or is it now pointing south (meaning that the helicopter must have yawed during the maneuver)? From your description, it sounds like you're saying that as the helicopter flies in a semicircle, it never flies backwards and never yaws, which is practically impossible. $\endgroup$ – Terran Swett May 17 at 22:11
  • $\begingroup$ I find the case where a helicopter performs a turn largely by yawing and then braking with cyclic much more interesting... of course the wind moving across the body of the helicopter make this harder to do. $\endgroup$ – Michael May 18 at 0:59
  • $\begingroup$ @TerranSwett -- re "I want to make the point that the helicopter is not yawing/turning on its own axis"-- I think what he really meant was that the turn is not centered around the aircraft's own vertical axis. Not that the helicopter's yaw rate is zero. There is some room for further clarification here, but I think he's basically describing a normal coordinated turn. $\endgroup$ – quiet flyer May 19 at 1:50
  • $\begingroup$ (Presumably meaning the yaw string is centered, which in helicopters, may mean that the ball is a little off center, due to the side thrust generated by the tail rotor?) $\endgroup$ – quiet flyer May 19 at 1:57
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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.

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  • $\begingroup$ While small and due to other phenomena, there is adverse yaw in a helicopter. Typically all four controls are moved to turn and maintain altitude & speed. $\endgroup$ – Mat Jun 13 at 19:27
  • $\begingroup$ Yes there are yawing effects, but not adverse yaw in the aileron sense which was my main point. $\endgroup$ – John K Jun 13 at 21:14
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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

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