Why Do RC Helicopters Have Two Rotors?


Why Do RC Helicopters Have Two Rotors?

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Have you ever gone to purchase an RC helicopter and realized that some of them have two rotors while others of them only have one? Maybe you are wondering if two is better than one, or if there is even a difference. Well, in this article we will go over everything you need to know about RC helicopters and why they sometimes have two rotors. 

So why do RC helicopters have two rotors?

Although not every RC helicopter has two rotors, the ones that do are called Coaxial Helicopters, and are made for beginners. These Coaxial Helicopters have no tail rotor, and are easier to learn on then a regular RC helicopter. 

If you want to see our top RC Coaxial Helicopters that we like, you can view them by clicking here.

If you want to know more about RC helicopters with two rotors, you will want to keep reading this article. You can also check out this video to learn all about coaxial helicopters. 

Coaxial Helicopters

RC helicopters with two sets of main rotors are coaxial RC helicopters, and these helicopters have their rotors one above the other, and no tail rotor. RC helicopters with two rotors can be beneficial to beginners because they offer the easiest learning curve when you’re speaking of orientation age flight. Coaxial helicopters are often referred to as helicopters that are flying themselves. This means that even without having a lot of control, beginners can still fly this kind of helicopter. 

Advanced hobbyists would not typically prefer this kind of helicopter because it limits the amount of control that they can have over the flight and hence, frustrates them. The thing is that the less control you have over your helicopters, the less equipped you are to handle sudden situations, but this is quite normal with beginners. Advanced hobbyists, on the other hand, would not appreciate this as they are already used to handling sudden breezes and obstacles like birds. This is why the coaxial helicopters are best suited for beginners.

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For advanced users, the coaxial helicopters can be quite frustrating because the advanced users would rather have more control than let the helicopter fly itself.

Tandem Rotor Helicopters

Tandem rotor helicopters are also two-rotor helicopters, but the layout of the rotors are different from that of coaxial helicopters. These tandem rotor helicopters come with two big horizontal rotor assemblies mounted one in front of the other.

Single rotor helicopters, on the other hand, require a mechanism to neutralize the yawing movement that the single large rotor produces. This is something that is normally done by coaxial rotors, a tail rotor, and the notary systems. However, tandem rotor helicopters make use of counter-rotating rotors, with each rotor canceling out the torque of the other rotor. This is why all the power coming from the engines can be used for a lift while a single rotor helicopter uses some of the power from the engine to counter the torque. Alternatively, you can mount two rotors in a coaxial configuration.

Advantage Of Tandem Rotors

  • Bigger center of gravity

The advantages of a tandem rotor system are that you can get a bigger center of gravity range, and you can also get good longitudinal stability. On the downside, the tandem rotor system is a complex transmission that creates the need for two big rotors.

The two rotors are connected by a transmission that makes sure the rotors are synchronized and that these rotors do not hit each other, even when an engine failure happens.

Tandem rotor designs get yaw by applying opposite left and right cyclic to each rotor. This action effectively pulls the two ends of the helicopter in opposite directions. In order to get a pitch, the opposite collective is applied to each rotor, and this decreases the lift that one end produces and increases the lift that the other end produces. This effectively tilts the helicopter forward or backward.

  • They can hold more weight
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One big advantage of tandem rotor helicopters is that they are able to hold more weight with blades that are shorter, seeing as there are two sets. The rear rotor works in the front rotor’s aerodynamic shadow though, and this lowers its efficiency. To minimize this loss, the distance between the two rotor hubs can be increased, and one hub should also be elevated above the other. Tandem rotor helicopters have a relatively lower disk loading than single rotor helicopters.

  • They demand less power

Also, when compared to single rotor helicopters, tandem rotor helicopters normally demand less power to hover and make a low-speed flight. Both configurations of helicopters normally would demand the same amount of power to be able to get a high-speed flight.

Contra-rotating Blades on a Coaxial RC Helicopter

This simply means that the main rotors spin opposite to each other, and as a result of this, they cancel out each other’s torque force. So, seeing as there is no torque when the two rotors are spinning at the same speed, the fuselage of the helicopter does not have any tendency to spin round in a specific direction.

You can achieve directional control by changing the speed of one of the rotors in comparison to the second rotor. When you do this, a small quantity of torque is generated, and that force normally forces the helicopter to yaw one way or another and, as a result, changes the directions of the rotors.

Coaxial RC helicopters are fixed pitch, and so you can control altitude by adjusting the speed of the motor and, therefore, the main rotor RPM, changes the associated amount of lift created.

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Choosing Between a Coaxial Helicopter and a Single Rotor Helicopter 

We already noted that coaxial helicopters are a lot easier for beginners to use because these helicopters practically fly themselves. It’s a lot easier for beginners to learn how to fly with coaxial helicopters, and it will let them understand how to handle more complex helicopters in the future. If you are a beginner, you might want to go for the coaxial helicopters while advanced hobbyists will want to go for the single rotor helicopters.

Another thing to consider is the fact that coaxial helicopters are a lot cheaper than single-rotor helicopters. This is one more thing that makes it a good option for beginners. If the cost is an important consideration for you, you might want to go for the coaxial helicopters. Also, if you do not mind having something that is quite informal and does not necessarily look like a real helicopter, you have no need to pay more for a more expensive option.

A third consideration is the appearance, which would really depend on your personal preferences. If appearance is important to you and you do not mind compromising on movement, a unique rotor model that has a strong gyroscope system, as well as a weighted barbell, maybe a good option for you to consider. If you want a model that offers both though, you will need to spend some more money to get the better-advanced scroll bars that have unique rotor blades.

Basically, three things to consider when you’re making a choice are your level of expertise or experience, your budget, and your preference for appearance.

Conclusion

Now that you know why RC Helicopters have two rotors, you can decide if a Coaxial helicopter is the best RC Helicopter for you or not. You know that these two rotors are best for beginners, and if you are just starting off, you will definitely want to start with a helicopter like this

Matt Robbs

I love to spend time with my wife and 3 kids. There is no better way to get them off the couch and outside than for us to grab the RC cars or boat and enjoy the sunshine!

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