How Coaxial RC Helicopters Work

What is a coaxial RC helicopter? There are several different approaches to coaxial rc helicopter design. There are two main ways that the main rotors of a helicopter can be mounted. In conventional helicopters, one main rotor is mounted on top of the fuselage, and a smaller tail rotor is added to the end of the tail boom. In this system yaw is controlled using the tail rotor, and every other aspect of flight is controlled by altering the pitch of the main rotor blades. It is also important to have a tail rotor so that the torque from the main rotors can be canceled out. Torque is caused by the main rotor spinning in one direction. Because of Newton’s laws of physics (for every action, there is an equal and opposite reaction), the nose turns in the opposite direction.

How Coaxial Helicopters Work

Instead of using the tail rotor to control the yaw, two main rotors can be mounted on the helicopter, and spun at different rates. The thrust difference will cause the nose of the helicopter to turn. This duel rotor design is employed in several full scale helicopters, including the CH-47 Chinook, frequently used as a military
transport helicopter because of its immense lifting capacity. The same principle applies to remote control helicopters, but most of the time we choose to mount each rotor on the same axial, hence the term “coaxial”.

Paired rotors spinning in opposite directions

The rotors of a coaxial helicopter need to spin in opposite directions to cancel out the gyroscopic force. On some helicopters, both rotors are on top of each other The main axial of a coaxial helicopter actually consists of two separate axils, one mounted inside the other. Each sub axial is connected to a gear at the base of the shaft, and each gear is attached to an electric motor. These two motors operate independently of each other, so varying the speeds of each rotor is possible.

Since the rotors need to spin in opposite directions, the top and bottom rotor blades are curved in opposite directions. This is because each rotor needs to be pointed into the air flow in order to work. The bottom rotor usually rotates in a clockwise direction, while the top rotor rotates in a counterclockwise direction. It is important to note this if you need to replace your helicopters rotor blades. Your helicopter will not fly if they are installed incorrectly.

Two Channel Coaxial RC Helicopter Design

It is possible to build a coaxial helicopter so that it only needs two main rotors, and eliminate the tail rotor entirely. Tilting the main rotors forward slightly, results in a constant forward movement. An excellent example of this simple design is our Firefly RC Helicopter, which is recommended for beginners due to it’s simple controls.

Three Channel Coaxial RC Helicopter Design

There are other cases where a tail rotor is still added to a coaxial rc helicopter. The tail rotor is placed in the same direction as the main rotors. This allows pitch control, so the forward and reverse rate of the helicopter can be changed. This means that you can fly backwards, forwards and even hover. The Micro Mosquito rc helicopter uses this design.

Four Channel RC Helicopter Design

Even though the coaxial design is most frequently used in small, fixed pitch rc helicopters, it can also be used for models with cyclic collective pitch. The only difference between these models and the conventional designs is their lack of a tail rotor. As with the models above, yaw is controlled by changing the rate at which each rotor spins, but the rotors can change their pitch. This allows the helicopter all four degrees of freedom: pitch, bank, throttle, and yaw. The Esky Lama V4 uses this design, making it a good all around RC helicopter.

Benefits Of The Coaxial Design

• The simple design leads to a low cost.
• Because yaw is controlled with the main rotors, pitch can be controlled with the tail rotor.
• This design produces a great amount of stability.
• Because they are stable, these helicopters are a great way to learn how to fly.

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Draganfly Innovations Inc.
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