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So occasionally I will be flying my rc helicopter and I turn it left to right (rudder) but see nothing moving on the helicopter. On an aircraft there is a vertical stabilizer that has a moving rudder. So how does a helicopter work? The same thing occurs with my quadcopter.

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In helicopter, the yaw control is usually obtained by adjusting the pitch of the tail rotor, that changes the 'thrust' produced by the tail rotor; this rotates the helicopter about its yaw axis.

Helicopter Yaw

Source: cfidarren.com

In case of helicopters without a tail rotor, the yaw control is obtained in different ways. The NOTAR used a method similar to the tail rotor, by varying the thrust. In case of tandem rotors (like Chinook) , the yaw control is obtained by differential lateral cyclic.

Tandem rotor yaw

Source: tech-mp.com

The quadcopters obtain yaw control by adjsuting the speed of the rotors. In quadcopter, two rotors (say 1 and 3) rotate in one direction, while the other two (2 and 4) move in the other. By slowing down 1 and 3 while speeding up 2 and 4, you can make the quadicopter yaw to the left. The torque of 2 and 4 spinning to the right makes the body spin to the left. Conversely, by slowing down 2 and 4 while speeding up 1 and 3, the quadcopter yaws to the right.

Quadcopter Yaw

Source: safaribooksonline.com

In case of coaxial helicopters like the Kamon Ka-25, the yaw control is obtained by varying the torques (i.e. by varying the pitch) of both the main rotors simultaneously in opposite direction.

Coaxial yaw

Source: simhq.com

Coaxial helicopters (like Kamov Ka-25) do have movable rudders like aircraft for use in forward flight as it reduces the main rotor adjustment required and is more effective.

Helicopter rudder

Ka-25 rudder, image from travelforaircraft.wordpress.com

The image below shows the control methods used in different types of helicopters.

Helicopter controls

Image from unicopter.com, credited to Rotary-Wing Aerodynamics.

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  • $\begingroup$ So basically the blades lean to the right side and the helicopter turns to the right side like a rudder $\endgroup$ – Ethan Nov 6 '15 at 14:09
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    $\begingroup$ @Ethan No! The blades don't "lean". The rotor disk is titled, so the thrust vector now has a horizontal component. It's the horizontal component which causes movement in the Y-axis or rotation around the Z-axis. This has been explained several times in questions you have asked. If there is anything in this comment that you do not understand, ask, since if you do not understand this comment, then you do not understand how helicopters fly. $\endgroup$ – Simon Nov 6 '15 at 16:02
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Helicopters do not have rudders.

They have tail rotors. You yaw left and right by varying the pitch of the blades, therefore varying the thrust they generate to counter the torque from the main rotor.

From Wikipedia.

enter image description here

Some helicopters use "NOTAR" (NO TAil Rotor) or ducted fans. The duct is rotated with the anti-torque pedals which varies the horizontal component of the thrust.

enter image description here

Quadcopters yaw by changing the speed, and therefore the thrust, of the rotors individually to "bend" the quadcopter.

From the UAV society blog

http://uav-society.blogspot.co.uk/2014/06/quadcopter-mechanics.html

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  • $\begingroup$ Do you know of any picture that could show this $\endgroup$ – Ethan Nov 5 '15 at 19:48
  • $\begingroup$ @Ethan Have you moved the rudder stick when your helicopter is on the ground and the rotor isn't spinning? Isn't there a servo somewhere connected to the tail rotor with a linkage on your helicopter? $\endgroup$ – Steve Nov 5 '15 at 21:52
  • $\begingroup$ There are a few helicopter designs I've seen that do have moving rudder surfaces. These tend to be twinrotor designs with no tail rotor, like the Ka-50 Hokum (which has an all-moving rudder). At high forward speed, it's more efficient to use a rudder surface to yaw than to alter relative torque of the main rotors. For the same reason, the AH-64 Apache has an all-moving stabilator, which helps to pitch the aircraft in combination with blade pitch to avoid stressing the rotor blades or hub at speed. None of these would apply to most RC helicopters. $\endgroup$ – KeithS Nov 5 '15 at 21:54

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