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Understanding Coaxial RC Helicopters


Coaxial RC helis are perfect for everyone. These helis are especially good for beginners. They are small and easy to control; there are various coaxial heli models available.

These helicopters are extremely popular because they are very stable and easy to maneuver. The bodies of coaxial RC helis are generally made of plastic or sturdy foam and the blades are made of plastic or soft nylon.

What You Need to Know About  Coaxial RC Helicopters

Coaxial vs Conventional RC Helicopters – What’s the Difference

Normally a helicopter that has a single main rotor deals with “Translation Tendency” or “Torque effect”. As the main rotor turns, torque is generated. Turning the fuselage in the opposite direction of the rotation of the main blade. To counteract this tendency, the tail-rotor uses thrust to compensate against the torque effect. This prevents the helicopter from gyrating completely out of control. The amount of push or thrust produced by the tail rotor can be changed by slowing or speeding up the rotor if it is fixed pitch or if it has variable pitch blades, changing the angle of the pitch to adjust the yaw or heading of the helicopter. This is a more difficult type of helicopter to fly. But, once mastered, flying a collective pitched helicopter is extremely rewarding. Co-axial blades

Coaxial RC helicopters don’t need a tail rotor, instead of a single rotor they have two main rotors. Co-axially mounted – one on top of the other and since they are rotating in opposite directions, the torque effect is cancelled. If both rotors are turning at the same speed, the helicopter will not have the nose drifting tendency that a regular helicopter experiences. But, by altering the rotation of the individual rotors, yaw can be induced to turn the helicopter, providing positive heading control. So, the yaw can be controlled by changing the speed of the main rotors, and the pitch can be controlled with the tail rotor.

Coaxial RC Helicopters – How Do they Work

There are different ways that coaxial RC helicopters can be designed. The main rotors of an RC helicopter can be mounted in two ways.

In conventional helicopters, a main rotor is mounted on the top of the fuselage, and a smaller tail rotor is added to the end of the fuselage. The tail rotor is used to control the yaw, and every other aspect of flight is controlled by changing the pitch of the main rotor blades. It’s also necessary to have a tail rotor so that the torque from the main rotors can be canceled out. Torque is created when the main rotor spins. For every action, there is an equal and opposite reaction, so the nose turns in the opposite direction.

The coaxial RC helis achieve their stability from the two rotors. They are stacked vertically on each other. These two main rotors spin in completely opposite direction. The reactive torque which is produced by one rotor is nullified by the counter reactive torque produced by the other.

Besides using the tail rotor to control the yaw, two main rotors can be mounted on the helicopter and spun at different rates. The difference in thrust causes the nose of the helicopter to turn. This duel rotor design is used in several full-scale helicopters. The CH-47 Chinook is a good example of this duel rotor design and is frequently used as a military transport helicopter because of its large lifting capacity. RC Helis use the same principle, but most of the time each rotor is mounted on the same axial, hence the term “coaxial”.

Twin rotors that spin in opposite directions

The rotors of a coaxial helicopter need to spin in opposite directions to cancel out the gyroscopic force. Also, the two rotors produce an additional gyroscopic effect which is responsible for further increase in stability and control of the coaxial RC heli.

On most coaxial helicopters, both rotors are mounted on top of each other. The main axial of a coaxial helicopter is actually two separate axils. One axial is mounted inside the other. Each sub axial is connected to a gear at the base of the main shaft, and each gear is connected to an electric motor. These two motors operate independently of each other, so the speed of each rotor can be changed.

So, the coaxial RC helis have separate motors for driving each rotor. Each rotor is responsible for driving the main gear. The two shafts for the main rotor are turned by two gears. The lower rotor is powered by the outside shaft which is hollow. The upper rotor is powered by the inner shaft. The inner shaft rotates or spins inside the hollow shaft. The lift of the coaxial RC helis is controlled by the two electric motors.

Since the rotors need to spin in different directions, the top and bottom rotor blades are curved in different directions. This is because each rotor needs to be traveling into the airflow in order to work. The bottom rotor spins in a clockwise direction, and the top rotor spins in a counterclockwise direction.

They are also responsible for the yaw movement or turning movement of the coaxial RC helis. When one of the rotors is slowed down and the speed of the other is increased, the reactive torque produced by the one spinning faster will lead to the yaw movement which is caused by the tail rotor in the case of helis with a single rotor.

A special electronic board for mixing controls the yaw movement. The board is responsible for seamless mixing of the two motor speeds which produces the turn rate required.


Two-Channel Coaxial RC Helis

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. These helicopters are great for beginners due to their simple controls.

Three Channel Coaxial RC Helis

In some coaxial helicopters, a tail rotor is still added. The tail rotor is oriented in the same direction as the main rotors. The forward and reverse rate of the helicopter can be changed because this system allows pitch control. You can fly forwards, backward, and also hover with this kind of helicopter.

Four-Channel Coaxial RC Helis

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.

How The Coaxial Design Benefits RC Helicopters

The best thing about the coaxial RC helis is that they have a high degree of agility because of the complete cyclical controlling. Lower rotors of the coaxial RC helis come with swash plates which aid in the cyclical controlling. This allows the coaxial RC helis to hover, move left or right and also fly backward or forward.

The main rotors spin in opposite directions, which gives the helicopter stability. This makes them a good way to learn how to fly, as they are very stable.

Many are small, much easier to hover, and stable enough to fly in your own living room. That makes coaxial RC helicopters an ideal type of helicopter for the novice, to begin with. So, as a beginner, they will provide you with a basic skill set that is needed to learn to fly RC helis. However, the major drawback is that the coaxial RC helis are not capable of acrobatics and hence, they may not be as fun as their collective pitch single rotor counterparts.

It won’t be long until you are moving your way up to the bigger and better helis. If you take care of your coaxial copter there are many retailers that will take a trade-in if you are looking at moving up. Ensure that you perform proper maintenance and try not to have too many rough landings or crashes.

guest post by Cordell Karman

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