Coaxial Benefits

    The Advantages of the Gyrodyne Contra-Rotating Coaxial Rotor Helicopter Configuration.

The following information is from Mr. Peter J. Papadakos' private working papers concerning the Coaxial benefits.......

    When Gyrodyne won the pilot-less helicopter ASW (anti-submarine warfare) program, competing against Kaman Helicopters, on December 31, 1958, it did so not just because Gyrodyne's coaxial rotor system demonstrated a higher payload capacity but also because of the many other benefits a coaxial rotor system provided for, given the need for a small sized airframe to operate from small destroyer-sized flight decks, which it did from 1963 to 1970 as the Drone Anti-Submarine Helicopter (DASH). Below are just a few of the benefits the U.S. Navy realized using the  Gyrodyne Coaxial Rotor system for their 1960's version of the VTUAV (Vertical Takeoff or Landing, Tactical Unmanned Aerial Vehicle).

Ultimate Compactness: The Gyrodyne Coaxial presents the ultimate in compactness for small ship decks as the fuselage is entirely functional (carries no rotor torque reactions) with no need to provide either a long boom for a tail rotor, or an overly long fuselage for the purpose of rotor separation. The components of the control system are short thereby improving control responses and effectiveness and the configuration presents the least vulnerable area of critical components. Accordingly, the wetted area of the Coaxial on the same payload basis is much smaller than either the tail rotor or the tandem configurations, thus allowing for multi-coaxial vehicle storage in small hangar decks and therefore increasing shipboard multi-mission capabilities and utilization.

High Useful Load: The absence of a tail rotor from the Gyrodyne Coaxial permits all of the engine power to be used by the rotor system for lifting purposes. Therefore, in comparison with a tail rotor configuration, the useful load of the Gyrodyne Coaxial is higher. What about Multi-rotor configurations? The substantially lower weight and the lower transmission and shaft power losses of the Coaxial as compared to the tandem configuration gives the Coaxial a useful load advantage over the tandem or any other multi-rotor configuration.

Safe Deck and Ground Characteristics: In cross winds on a rolling pitching and heaving ship’s deck, or on the ground, the following make the handling of the Gyrodyne Coaxial much simpler than any other type: (1) The inherent torque neutralization characteristics of the Coaxial Rotor System eliminates dangerous inertia and torque effects, ground looping and cross wind effects during quick starts and stops of the rotor system; (2) The use of the semi-rigid rotor system assures freedom from ground resonance; and finally, (3) the automatic gust locks in the Coaxial Rotor System prevent blade flapping at low

Low 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 mission 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:

    (1) 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.

    (2) 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 it is slightly higher as compared to other multi-rotor systems.

    (3) The total weight of the fuselage, transmission, and rotor system of the Coaxial Rotor Helicopter is found to be slightly 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.

Complete Symmetry of the Rotor System: The symmetry of the Coaxial Rotor System permits the same aerodynamic efficiency and controllability for flight in any direction; a feature only found in the coaxial.

Simplified Rotor System The Gyrodyne 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 possessing 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. The size of the rotor diameter in the Gyrodyne Coaxial is totally independent of the fuselage. This feature, of disassociating the rotor diameter size from the fuselage, becomes considerably important in heavy lift helicopters.

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 Gyrodyne Coaxial Helicopter yields the following advantages: 


(1) For translational flight along any axis, the movement of only ONE control is required; 


(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.

Low Tooling and Manufacturing Costs: On a dollar-per-pound basis the Coaxial has an advantage over the other configurations because of of its lower empty weight; this advantage is further amplified by the following two features:


The symmetry of the rotor system and the transmission reduces approximately by one half the number of individual components.


The freedom of torque reactions of the fuselage calls for simpler fuselage structural design.

Optimal Transmission Design: In a Coaxial configuration, the inherent feature of splitting the power input into two paths (see right) 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, and with only a small overall weight increase per added engine. This unique feature of the Coaxial transmission achieves greater importance as the size of engines and number of engines increases as required to satisfy the need for heavy lift helicopter cranes.

Modular Construction: The closed-loop torque-balanced Coaxial Rotor System eliminates torque reactions on the fuselage, thus making the fuselage a totally independent body from the rotor-transmission-engine combination.

    In the Gyrodyne Coaxial, 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 a major subassembly, referred to hereinafter as the Propulsion-Power Plant Package. The independence of the Propulsion-Power Plant Package from the fuselage yields several advantages, the primary ones being:


Design and Manufacturing Flexibility


Lower Structural Weight


Growth Potential


Modular Construction

    To further emphasize the independence of the Propulsion-Power Plant Package from the fuselage, the following examples are presented. Once the design of a Propulsion-Power Plant Package has been developed, a number of functional fuselages can be designed and adapted to it without causing a need for redesign of the Package.

    Within limits, the opposite is true. A fuselage can be utilized with somewhat different Propulsion-Power Plant Package without calling for redesign of the functional fuselage. The economics of this feature cannot be over-emphasized, especially during a period when requirements are constantly changing (also known as requirement creep).

Growth Potential: The many growth areas that a Coaxial helicopter permits are as follows:


As stated above, the fuselage design of the Coaxial is purely functional and independent of the size of the lifting system (Propulsion-Power Plant Package). Therefore, increase in size of one of the major subassemblies 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 in the transmission per additional engine. This feature permits proportionately small change in the transmission for substantial growth. (The feature is not available in the single rotor or the other multi-rotor configurations.)


For a given size of components - from the industrial capacity standpoint - double power can be handled by the coaxial (transmission-rotor system combination) as a result of the inherent division of power between the two rotors balanced torque-wise in closed-loop.


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

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