Coaxial RC Helicopters
They Still Have A Place In Our Hobby

by John Salt 

I still think micro coaxial RC helicopters remain to be one of the most amazing and fun products to have hit the RC market in years. Yes, they are now being overshadowed by quad-rotors and fixed pitch helis with electronic self-level stabilization as entry level helicopters for beginners, but coaxials are still introducing many people to this wonderful hobby in the toy versions. They also look like a "true helicopter". For many of us "rotor heads", that's very important.

Blade mCX2 Coaxial RC HelicopterBlade mCX2 Micro Coaxial Heli

The cost is low, the fun is high... They work well for just about every age group and ability. They are the perfect introduction for first time flyers to the RC hobby as I've already mentioned on my "RC Helicopters For Beginners & Kids" page; yet experienced RC heli and airplane pilots continue to find them enjoyable for some easy going indoor flying when we just need a bit of a "flying fix" and can't venture outside.

Even though it was discontinued a good number of years ago, I still very much enjoy flying my Blade CX3 indoors during the winter months for a little bit of "scale" fun. In the hundreds of flights I have had with it, it continues to work and fly so well. 

Scale Micro Coaxial RC Helicopter IndoorsFlying My Coaxial Scale MD520N Indoors On A Cold Winter Sunday Morning - Better Than A Cup Of Coffee :-)

If you are interested in RC helicopters but are a little intimidated by the complexity and cost of single rotor hobby grade collective pitch helis; Coaxials are the perfect solution.

They not only look like conventional helicopters, the hobby grade coaxials use swashplate cyclic control just like real helicopters. In other words, if your main reason for thinking of getting into the hobby is because of your fascination with helicopters in general, micro coaxials are the obvious choice over micro quad-rotors that look nothing like a conventional helicopter.

Even though coaxials are easy to fly, many of the skills you learn on a hobby grade coaxial RC helicopter are somewhat transferable to single rotor hobby grade RC helis. This holds especially true for understanding the control reversals when practicing nose in hovers .

What Makes Coaxial RC Helicopters So Special?

Simple, efficiency & stability!

Unlike a conventional single rotor helicopter that only has one main rotor and a tail rotor to counteract the torque produced, coaxial helicopters have two main rotors stacked on top of each other.

Coaxial RC Helicopter Rotor System

Having two rotors spinning in opposite directions at the exact same speed produces equal amounts of torque from both.

Since the torque is equal, but occurring in opposite directions, it essentially cancels out (a state of torque equilibrium), and the helicopter won't yaw (turn).

No additional energy is therefor needed to power a tail rotor to counter the torque giving improved efficiency; which on an electric powered RC helicopter equates to longer flight times.

Having two spinning main rotors also adds rotor mass which produces a significant gyroscopic effect that helps stabilize coaxial RC helicopters.

In short – no other mechanical design is as efficient or stable. Remember me saying on the home page that all helicopters are unstable? Well, coaxial’s break this rule - unless of course your coaxial heli encounters the infamous Toilet Bowl Effect .

Nasa's Ingenuity Coaxial HelicopterNasa's Ingenuity Coaxial Mars Helicopter

It should therefor come as no surprise, NASA also decided to use the coaxial helicopter design for their very first Mars helicopter named the Ingenuity. Mars with an atmosphere 100 times thinner than Earth's, an efficient coaxial was the obvious choice.

How Do Coaxial RC Helicopters Work?

Coaxial RC Helicopter Main Gearing

All micro coaxial RC helicopters work the same way. They have two separate electric motors that drive each rotor. You can see this in the picture to the right.

Each motor drives a main gear. You can’t see the upper gear that well in this photo because it is hidden by the lower gear, but you can easily see the two motor pinion gears (the small brass ones).

At any rate, these two main gears turn two main rotor shafts. The outside shaft that powers the lower rotor is hollow and the inner shaft that powers the upper rotor is spinning inside the lower hollow shaft – obviously in the opposite direction – pretty simple.

Coaxial RC Helicopter DesignCoaxial RC Helicopter Mechanical Components

These two motors control both the lift of the helicopter by speeding up and slowing down. They also control the turning or yaw movement of the heli just like a tail rotor would on a single rotor helicopter. How?

If one rotor is slowed down a bit, and the other is sped up, the one that is turning faster will produce more reactive torque than the slow one and the heli will turn/yaw, just as if a tail rotor turn command was given.

This yaw movement is controlled by a special electronic mixing board that will seamlessly mix the speed of both the motors to allow the required turn rate while also making sure the overall lift remains the same.

Cyclic Control

Yes, as I already mentioned, hobby grade micro coaxial RC helicopters have a swashplate meaning they have cyclic directional control. There are certainly toy grade micro coaxials that don't have cyclic control and rely on either simple weight distribution or small horizontal tail fans that give them limited forward movement; but I'm focusing on hobby grade coaxials in this write up as it trumps toy grade flight response and precision.

Cyclic gives these helicopters some of the same agility that their more complex single rotor collective pitch big brothers have. The lower rotor has a typical swashplate to produce the cyclic control functions. Hover, fly forwards and backwards, left and right, it is all possible. Throw in some nice controlled pirouettes and you have a very functional and controllable bird.

Scale Coaxial RC Helicopter Flying OutdoorsCoaxial RC Helicopter Flying Outdoors

Coaxial RC Heli Recommendations

Blade's mCX2 electric micro coaxial helicopters is my top pic for several reasons.

Main one being it's pretty much the last decent 4 channel micro coaxial RC helicopter on the market that uses proper cyclic control.

It's fairly robust, looks good, has adequate parts support from most local hobby shops or online shops, and is of course fun and easy to fly.

The fact it's been on the market now for 10 years, is testament of it's good and lasting design.

Here's my full write-up of this neat little 4 channel coaxial RC helicopter.

Micro Coaxial vs Micro Quadrotor

Micro Coaxial vs Micro Quad Rotor RC HelicopterMicro Coaxial vs. Micro Quadrotor - Who's the winner?

I have been hearing a fair number of people stating micro coaxial RC helicopters are not going to be around for much longer because of micro quad-rotors.

I for one don't agree with that at all. Not because I dislike micro quads, I feel they are also a very good first time RC helicopter as well; but the one undeniable fact is they look nothing like a conventional helicopter.

I personally got into this hobby because I was always fascinated by real helicopters and I know many other people who continue to get into the hobby for the exact same reason. If you fall into that category yourself and want something simple and fun to fly, a micro coaxial RC heli still is, and will remain to be a good RC helicopter to start out on.

On the flip side of the coin; if you really don't care about the true helicopter looks or how they work, then I would agree; a micro quad rotor is probably the better route to go. If you want more information about this, again please take a peek at my RC Helicopters For Kids & Beginners page or to find out more about quad-rotors, feel free to take a peek at my quadrocopter page .

To conclude my little coaxial helicopter write-up, I can't resist showing this video of a full size single seat turbine powered coaxial helicopter. I can't think of many "big kids" who would not want this rascal parked in their garage.

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