Coaxial Drive Systems for Advanced Coaxial Helicopters


The conventional single rotor helicopter is the most common rotary-wing flight device.  However, it is hard for everybody to learn to hover a single rotor helicopter.

Single rotor helicopter requires a small tail rotor to overcome torque, to achieve balance, and to provide directional control. 

This is why there is a small rotor mounted perpendicular to the main rotor at the very end of a long tail boom. This small tail rotor is necessary to satisfy the requirements to control torque and directions. 

Since this small tail rotor is far in the back of the helicopter that the pilot usually cannot see, causing some very undesirable effects and hazards as described in the FAA's Helicopter Flight Handbook. 

The tail rotor has also been the main factor for a high percentage of helicopter accidents, creating dangerous situations in both "hover" and "forward" flights.

The advantages of the coaxial rotor configuration becomes apparent when there is no tail rotor.

Without a tail rotor, a helicopter is free from undesirable hazards. 

Without a tail rotor, there is no more a long tail boom. A shorter helicopter with a smaller footprint can now make the use of a home-based helicopter garage a reality. 

YOSHINE began its efforts on the CDS development in the early 2000's. 

After years of focused efforts, a new generation of CDS designs has emerged.  Hazards of the single rotor helicopters is now reduced or eliminated with the YOSHINE CDS. 

Since the first CDS make it's debut at the HELITECH Exhibit near Cambridge, UK, in 2003, the YOSHINE CDS has been well received by helicopter experts and enthusiasts while on display at many other international trade shows and exhibits. 

YOSHINE CDS offers a no-tail-rotor technology that comes complete with an integrated coaxial rotor system, capable of accepting cyclic, collective, and yaw control inputs simultaneously.

Coaxial helicopters may be developed with a CDS from group up or integrated into an existing or modified airframe.

Mateo from Italy visited YOSHINE CDS-1 in 2008; 10 year old from Swiss with CDS-2 (Left).

Although "Helicopters for Everybody" may still beyond reality, we are pleased to have achieved our objective of developing a CDS to help anyone who wants to develop their own coaxial helicopters. 


Chris from Boston USA visited YOSHINE in 2008 examining a CDS swashplate component.


An EZYCOPTER built with a YOSHINE CDS as a testing model.

A typical CDS model

Background and Advantages of Coaxial Helicopters with a Yoshine CDS

During the first 100 years of aircraft development, fixed-wing aircraft received most of the attention. Interestingly enough, however, it was helicopter flight that was first envisioned by man.

The Chinese, in ancient times, played with a hand-spun toy that rose upward when rapidly revolved. This, in fact, marked the first helicopter flight concept.

However, it was in 1490 that the famed Italian, Leonardo da Vinci, became the first to put down on paper a design for a man powered spiral winged device that resembled the modern coaxial helicopter.

The word "Helicopter" is derived from ancient Greek terms "helix" (spiral) and "petron" (wing).

Before the Wright Brothers flew the world's first airplane, Igor Sikorsky had already built a coaxial helicopter in Russia. Since then, many famous names have been known in helping to shape up the final design and development of coaxial helicopters, such as Cornu, Asboth, Pescara, De Bothezat, Berliner, Bendix, Hiller and others.

Coaxial designs are attractive due to their basic simplicity: the power train is shorter and the airframe can take many shapes.

Counter-rotation eliminates feeding torque into the airframe. In hovering flight the lift force is only vertical, there is no tail rotor producing a side force requiring constant pilot intervention and hence the complexity of piloting a coaxial helicopter is minimized.

In the early helicopter period many extraordinary models were developed by a number of great thinkers. However, those pioneers were missing two essentials: (1) a true understanding of the nature of lift and, (2) an adequate lightweight engine with sufficient power.

The breakthrough came at the end of the nineteenth century when the internal combustion engine was invented. This event made it possible to develop full-sized helicopters with enough power. Other problems then surfaced as the early pioneers began designing and testing their vehicles.

Overcoming torque, which is the effect produced by a spinning rotor to force the fuselage to rotate in the opposite direction as the engine, became the first major issue to be resolved.

The Invention of the "Swashplate"

The second problem related to the dissymmetry of lift, which is the action that caused the early single-rotor helicopters to flip over when translating from hovering to forward flight. This problem confounded the early pioneers until the introduction of independent freedom of blade motions made possible by the invention of the "swashplate".

The swashplate provides a means of varying the pitch of the blades in a cyclic fashion as they rotate around the central shaft. The provision of cyclic pitch control allowed the lift to be equalized on each side of the shaft and eliminate the tendency of the helicopter to tip over sideways.

On November 13, 1907, the French pioneer Paul Cornu lifted a twin-rotor helicopter into the air entirely without assistance from the ground for a few seconds.

At about the same time, Henry Berliner created the first powered rotorcraft that successfully made a controlled flight. Berliner's helicopter flew about 100 yards at an altitude of about 15 feet, and the flight was completely controlled by a pilot.

Later, the invention of the hinged rotor blade, by the Spanish engineer Juan de la Cierva, coupled with the incorporation of a swashplate, laid out the foundation for the eventual development of the helicopter as a practical form of air transportation.

Various Helicopter Designs

During the helicopter's evolution, many designs have been developed and produced, including the single rotor, the coaxial rotors, the tandem rotors, and many other rotor arrangements. 

With the exception of the single rotor design, all other designs have been involved with two or more rotors. Most multiple rotors are arranged in symmetrical harmony or in a balanced fashion.

The system that YOSHINE has focused is the coaxial rotor design. This design has two rotors mounted one on top of the other on a single axis and rotating in opposite directions.

Early pioneers like Peter Papadakos in the U.S., and the Kamov Design Bureau of Russia put this design to its ultimate for military applications. The Kamov KA-50 and 52 are but two attack helicopter examples of the coaxial rotor configuration.

(1) The single rotor design

This is the most common helicopter design that has a main and a small tail rotor, made famous by Sikorsky & Bell by selling thousands to the U.S. Government.

(2) The coaxial rotor design

This design has two rotors mounted one on top the other on a single axis and rotating in opposite directions. Both Peter Papadakos of the U.S., and Kamov Design Bureau of Russia perfected this design primarily for military applications. Russian Kamov KA-50 was produced as a counter force for the U.S. Apache with this design.

(3) The tandem rotor design

This design also has two rotors, one in the front and one in the rear of the aircraft. This designed was pursued by Frank Piasecki and finally purchased by and made famous by the Boeing Aircraft Company.

(4) The side-by-side rotor design

This design also has two rotors arranged side-by-side and V-12 was built in early Russia. Not much is known what happened to the aircraft but many similar aircraft seemed to have been designed around the concept.

(5) The intermeshing rotor design

This design utilizes two intermeshing rotors, one located on each side of the aircraft. Charlie Kaman of Kaman Corporation, USA, was the pioneer for this design.  His aerial trucks have been sold around the world.

Why Single Rotor System Dominates Modern Helicopter Design?

Since 1941 when Sikorsky obtained an order to mass-produce his single rotor system helicopters for the US Government, the single rotor system has dominated modern helicopter design.

However, in the late 1940's, Peter James Papadakos of the Gyrodyne Company started the design, development, testing, and production of coaxial helicopters.

The Gyrodyne coaxial design varied in size and complexity and ranged from small single seat helicopters to radio controlled models QH-50 series of coaxial UAV helicopters.  In the mid 1970's, Gyrodyne lost its competitive position to Sikorsky and Bell after producing thousands of small coaxial helicopters for the US military and UAV's for anti-submarine warfare operations. This, coupled with compounded financial difficulties, due to escalating costs of engines and materials, they eventually ceased their coaxial helicopter development activities.

Kamov Design Bureau of Russia has concentrated their efforts on coaxial helicopter designs and developed the only coaxial attack helicopters in the world, KA-50 and KA-52, to rival the US Cobra, Apache, and "Comanche" helicopters.

Hence, for the past 50 years due to the complexity and difficulty of pilot training, extreme costs that only military can afford, coupled with strict government regulations, the personal helicopter industry has never reached a mass consumer market. Futurists have predicted from time to time that it will become a mass-market product. But it never happened.

At YOSHINE, we believe it was time and have, in recent years, taken a different approach and devoted considerable efforts to the design and development of an affordable coaxial helicopter.

Coaxial helicopters with twin rotors provide multiple benefits for personal flight. For instance, they provide increased lift per horsepower and improved hovering capability over traditional single rotor helicopter craft.

Coaxial helicopter rotors are driven by a single drive shaft thus providing improved balance and flight stability.

Counter rotation not just eliminates the need for a tail rotor but it also eliminates general gyroscopic effects that make flying a single rotor helicopter difficult.

People throughout history have wanted to experience the joy and thrill of moving freely above the ground, to hover and to fly vertically at will.

People want to FLY, but opportunities are so limited due to the high costs and extreme complexity of helicopter flying, until now.  Introducing.....the YOSHINE coaxial helicopters...

The YOSHINE Coaxial advantages

At YOSHINE, we offer a uncomplicated "complicated" CDS

YOSHINE EZYCOPTER incorporates the best features for a small coaxial design with distinct engineering innovations:

1. Ultimate Compactness:

The EZYCOPTER presents the ultimate in compactness and demonstrates its capability in operating with a high payload while requiring a minimum amount of power. Under the same payload condition, the EZYCOPTER is smaller and lighter than either a single rotor or tandem rotor configuration. This reduces, significantly, the amount of space required for vehicle storage and permits operations from anywhere where there is a small takeoff and landing area available.

2. Higher Useful Load:

With the absence of a tail rotor, the EZYCOPTER allows all of its engine power to be used by the coaxial rotor system for lifting purposes. Therefore, in comparison with a tail rotor configuration, the useful load of the EZYCOPTER is higher, with a similar power rating. Also the lower weight of the coaxial design and the less power loss due to shorter shaft power transmission provide the EZYCOPTER a higher useful load advantage over the tandem or any other multi-rotor configuration.

3. Safer VTOL Characteristics:

In cross winds, or on a rolling pitching takeoff, or when landing, the control of the EZYCOPTER is much easier due to the following:

(a) The inherent torque neutralization characteristics of the single coaxial rotor system eliminate dangerous inertia and torque and cross wind effects during takeoff and landing;

(b) The use of the collective and the cyclic makes precision flight controls possible;

(c)  The use of the correlation between the throttle and the collective makes automatic flight control easier and safer.

4. Lowest Empty Weight:

The feature that makes the fuselage independent of the lifting system dynamics permits the design of the fuselage to be strictly functional as related to requirements. Accordingly, the size of the coaxial rotor system fuselage for the same useful load is smaller than any other type and structurally simpler, resulting in lower fuselage weight.  Consider these other weight savings:

  • The weight of the coaxial transmission system for a given horsepower is lighter than the total weight of the two or more transmissions systems utilized in either the anti-torque tail rotor or tandem rotor configurations.

  • The total blade area of the coaxial rotor is essentially equal to the blade areas of the main rotor of a comparable single rotor and is higher as compared to other multi-rotor high-disk loading systems.

  • The total weight of the fuselage, transmission, and rotor system of the coaxial rotor helicopter put together is lower than that of an equivalent engine horsepower of a tail rotor configuration and substantially lower than that of the tandem or other multi-rotor configurations.

5. Complete Symmetry of the Rotor System:

The symmetry of the EZYCOPTER coaxial rotor system permits the same aerodynamic efficiency and controllability for flight in any direction; a feature only found in true coaxial helicopter with precision collective and cyclic controls.


6. Simplified Rotor System

The EZYCOPTER coaxial utilizes the semi-rigid type of rotor system without the need for use of mechanical stabilizing devices, thus resulting in a simpler rotor system design with inherent excellent flying qualities. The simplicity of design yields benefits such as lower structural weight, manufacturing and maintenance costs. In addition, this rotor system makes the helicopter free from ground resonance.


7. Freedom from control cross-coupling:

Control cross-coupling exists in all other rotor configurations, causing control complexity, dangerous flight attitudes and vibration. Lack of control cross-coupling in the EZYCOPTER coaxial helicopter will yields the advantages as follows: 

  1. Only ONE control is required for transnational flight along any axis;

  2. Control along each axis is powerful, symmetrical, and unaffected by the controls along the other axes; 

  3. Comparable translational accelerations in all directions are obtainable; 

  4. Precision handling ability with excellent control even under adverse cross wind conditions and;

  5. Exact and excellent hovering positioning is excellent due to the symmetry of the coaxial rotor system.


8. Economic Tooling and Manufacturing Costs:

The EZYCOPTER coaxial has an advantage over the other configurations because of its lower empty weight; the following two features further amplify this advantage:   

  1. The symmetry of the rotor system and the transmission reduces approximately by one half the number of individual components as compared to single rotor configuration;

  2. The freedom of torque reactions of the fuselage calls for simpler fuselage structural design, resulting lower tooling and manufacturing costs, benefiting both the manufacturer and the users.


9. Optimal Transmission Design:

In a coaxial configuration, the inherent feature of splitting the power input into two paths results in a transmission design internally balanced, compact and capable of handling greater horsepower per engine input than any other configuration. The design is naturally suited for multi-engine inputs without creating external torque reaction problems. This unique feature of the coaxial transmission achieves greater significance as the size of engines can be increased or decreased as required to satisfy the need for individual requirements.


10. Modular Construction:

The closed-loop torque-balanced coaxial rotor system eliminates torque reactions on the fuselage, thus making the fuselage independent from the rotor-transmission-engine combination. And in the EZYCOPTER, all four controls (longitudinal and lateral cyclic, collective and directional control) are independent of each other and completely incorporated in the lifting rotor system. This feature makes it possible to consider the engine, transmission, rotor and its controls as major independent subassembly packages that yield the following advantages, further reducing acquisition costs:

  1. Design and Manufacturing Flexibility

  2. Lower Structural Weight

  3. Growth Potential

  4. Modular Construction

11. Growth Potential

This is one area that a coaxial helicopter promises the most. As stated above, the fuselage design of the coaxial is purely functional and independent of the size of the lifting system.

Therefore, increase in size of one of the major sub-assemblies does not affect the other. The coaxial transmission is naturally suited for multi-engine inputs without creating external torque reaction problems and with only small weight increase per additional engine. This feature permits proportionately small change in the transmission for substantial growth. 

This feature of the EZYCOPTER is not possible or available in the single rotor or the other multi-rotor configurations without major modifications and associated costs. 

The flying qualities of the EZYCOPTER coaxial are such as to permit higher disc loadings than single rotor helicopter without affecting controllability and fuselage design; thus permitting increase in lift capability without materially affecting the envelope of the vehicle.


12. Reduction & Elimination of Common Helicopter Flight Hazards

The U.S. Department of Transportation has published a Basic Helicopter Handbook. One of the chapters in it is titled, Some Hazards of Helicopter Flight.  Ten items of hazards have been listed to indicate that a typical single rotor helicopter has to deal with.  The unique EZYCOPTER coaxial design either reduces or completely eliminates these hazards.  The following list indicates which:

1. Settling with power


2. Retreating blade stall


3. Ground resonance


4. Low-frequency vibrations


5. Medium frequency vibrations


6. High frequency vibrations


7. Transition from powered flight to autorotation


8. Anti torque system failure in forward flight


9. Anti torque system failure while hovering


10. Height-Velocity Curve


Helicopters built with a CDS promise to be as easy to fly as a Cessna airplane, but without the burden or requirement of an airport runway.


A "Dream" Coaxial Drive Helicopter Demonstration with 4 little engines.


CDS duration test in 2005.                             Visitors from Russia in 2006.

Around the clock we work to advance cutting edge CDS technology.


A single seat coaxial helicopter with 200lbs payload may require a powerplant up to 80hp. A two-seat coaxial helicopter may require a powerplant up to 120hp.

Example: CDS-I Design Specifications:

1) # of Rotor Blades: 4 ; 

2) Upper and lower blades may be of equal length, or of slightly different length:

        Upper rotor blade length = 2250mm each.

        Lower rotor blade length = 2400mm each.

3) Rotor RPM = 750 ~ 800rpm

4) Rotor Blade Pitch Angles: 4 ~ 8 degrees

5) Horsepower : 50hp~ 100hp max.

6) Empty Weight: approx., 200 ~ 250kgs.

7) Takeoff Weight: 350kgs., max.

(Above information for reference only and subject to change without notice.)

Various previous & current coaxial helicopter designs.....




SAR Prototype with an OEM CDS" (Paris Airshow 2009)