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Understanding COUNTER-ROTATING Coaxial Rotor Design

Coaxial rotor designs have been used on military helicopters for the better since last 75 years. A coaxial rotor eliminates the need for a tail rotor and creates a safer, more stable machine.  To understand how coaxial design outperforms other helicopters, let's examine the physics.

The physics of helicopters

For single-rotor helicopters, lift is generated through the main rotor rotating. This rotation generates torque about the main helicopter, causing the main fuselage to spin around in the opposite direction.

Early engineers designed the tail rotor to counter this torque and keep helicopters stable. Tail rotors are generally much smaller rotors mounted on a perpendicular axis to the main rotor.

By controlling the speed of the tail rotor, the pilot can stabilize the craft as well as control the direction of the helicopter.

Slowing the tail rotor would cause the helicopter body to rotate in the opposite direction of the main rotor due to excess torque in that direction.

Speeding up the tail rotor would do the opposite. Along with direction, helicopter pilots can control the yaw of the craft by adjusting the angle of the tail rotor. By pitching the tail rotor slightly up or down, the pilot creates a moment arm through the helicopter, which in turn adjusts the yaw of the craft.

Why a coaxial design is better ？

Now that we understand the basic mechanics of single-rotor helicopters, we can begin to see why coaxial rotors might present some advantages.

By placing two rotors on a single axis and rotating them in opposite directions, a net-zero torque around the main body of the helicopter is created, keeping it very stable.

Through both mechanical means and electronic means, each rotor is perfectly timed and controlled to cancel out the net torque of the other rotor in real-time. This allows the coaxial craft to achieve rather significant hovering capabilities when compared to their single-rotor brethren.

When you think of helicopters, you think of vertical takeoff and the ability to hover. Remove those aspects, and the helicopter functions identically to a plane.

As a side note, vertical takeoff isn't exclusive to rotorcraft.  However, planes that harness the ability without rotors – mainly the harrier jet – accomplish the task with much less efficiency and stability.

A helicopter's ability to hover and be stable is synonymous with its quality of being a helicopter.

In coaxial designs, the improved ability to hover and maintain stable flight ultimately makes for better helicopters. Better helicopters mean that they are easier to control and much safer for the occupants.

Theoretically, if one rotor broke in a coaxial system, the craft could still be landed safely.

Lastly, the application of coaxial rotors means that there is no inherent need for the craft to have a gyroscope to provide stability. The rotational effects of both rotors provide for a near-perfect gyroscope, improving the stability of the craft once more.

Issues with coaxial helicopters

The first main fault is that the timing of the two rotor blades needs to be near perfect.

Speed and directional changes need to be achieved together.  Slightest fault in calibration essentially makes the aircraft unstable and impossible to fly.

A fault in calibration is worse than you probably think for the craft's ability to fly.

If the timing is off enough, coaxial helicopters won't produce enough lift to even leave the ground and end up just spinning on the tarmac.

On top of the need for accuracy in the tuning of the rotors, these rotors tend not to be as responsive as a single-axial rotorcraft.

When you make an aircraft more stable, you generally make precise movements harder to achieve – it's called a constant tradeoff in aerospace engineering.  For instance, while coaxial helicopters are safe and efficient, they are not well suited for applications where pilots need fine and precise maneuverability.

However, CoaxCopters are perfect for applications where precise hovering is needed.

The coaxial rotor design is one of the most prominent helicopter designs to date.

The stability of the design is getting more and more popular even military and rescue helicopters.

So next time when you are buying a helicopter, which design would you choose?

In 2003, the world's first "unmanned" coaxial helicopter with a payload up to 100kg was successfully developed and lift off in Taichung, Taiwan, by YOSHINE HELICOPTERS using a patented "CDS" technology!

2003年，祐祥載重100公斤的『共軸無人直升機 』在台中『漢翔公司』協助在漢翔園區起飛！

2003 CDS Shown at Duxford UK Helitech 2003

2005年，美國的PM科技雜誌報導, “EZYCOPTER by Yoshine Helicopters of Taiwan 為全球第一架「無尾旋翼」個人休閒運動「雙主旋翼」共軸直升機，未來也有國防軍事用途發展潛力。

傳統直升機《手排》飛控方式 vs. 共軸直升機《自排》解決方案

【CDS】傳動系統讓直升機起飛時，扭力自動平衡，將平衡『自動化』，解決了「扭力平衡」問題！

"CDS"：新一代無扭力直升機的飛控系統 專業廠商

"CDS"：潛在市場

（1）個人直升機：適個人超輕休閒運動飛行的直升機。

（2）無人直升機 載重遠距飛行的無人直升機，供「農、漁、牧」及「國防軍事」用途。

The Hybrid Coaxial Air Taxi

The Coaxial Helicopter of the Next Generation

One Step Closer to Zero Emission

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Safe and Reliable Electric Vertical Take Off & Landing.  Affordable and Sustainable solution.  New Electro-Hybrid drive, Long Range Electric Flight

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