Gyrodynes and Heliplanes

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It has been suggested that Gyrodyne Trademark be merged into this article or section. (Discuss)
For the company, see Gyrodyne Company of America.
For the use of Gyrodyne, as a trademark, see Gyrodyne Trademark.

A Gyrodyne is a heavier-than-air aircraft having some of the characteristics of a helicopter (where the rotor provides both lift and propulsion) and some of an autogyro (where the rotor provides lift only). In recent years a related concept, a gyrodyne with wings, has been promoted under the name Heliplane; a term which was originally used by Don Farrington to market the Air & Space 18A gyroplane.

There is controversy over the correct usage of the terms gyrodyne and heliplane. The terms compound helicopter or compound gyroplane are also used for such aircraft, although these definitions are not used consistently. The term gyrodyne is an official aircraft class within the rotorcraft category in US FAR Part 1: Definitions and Abbreviations; heliplane is an advertising term.

Contents

[edit] History

[edit] Gyrodyne concept

Once the initial challenges of rotary-wing flight had been solved with the development of Cierva's Autogiro, research began to focus on improving their range of abilities. Jump take-off gave autogyros limited VTOL capability, and work then addressed the possibilities of true VTOL and hovering.

In Russia and Germany, engineers such Anton Flettner moved the autogyro's propellor to stub wings to provide the anti-torque control that allowed the rotor to be driven by the aircraft's engine in flight. In forward flight, the aircraft would fly as an autogyro or helicopter. One such aircraft was the Flettner 184.

Early autogyros had stub wings which provided part of the lift in forward flight, but the main source of lift was the rotor. The primary purpose of the wings in these early autogiros was to provide efficient support for the flight control surfaces since cyclic control of the rotor had not yet been developed. Some attempts were made to stop the rotor and use it as a fixed wing, such as the HV-1, but cumbersome mechanisms and rotor instability during inflight conversions posed insurmountable problems at the then current level of technology.

In Britain, Prof. James Allan Jamieson Bennett (Chief Engineer of the Cierva Autogiro Company, Ltd.) developed a third distinct type of rotorcraft termed gyrodyne. This rotorcraft was described in US Patent 2,317,340 granted to the Autogiro Company of America (formed by Harold F. Pitcairn to license Autogiro patents in the United States) in 1943 as:

   
Gyrodynes and Heliplanes
 a rotary wing aircraft intermediate in type, hereinafter referred to as "Gyrodyne", between a rotaplane (with the rotor free for autorotation and an upward total axial flow through the rotor disc), on the one hand, and a pure helicopter (with the rotor driven, and a downward total axial flow through the rotor disc), on the other hand, that is with a mean axial flow through the rotor disc substantially zero at high forward speed.
   
Gyrodynes and Heliplanes

In other words, in helicopters airflow through the rotor is downwards; in autogyros airflow through the rotor is upwards; in gyrodynes airflow through the rotor is minimal.

Bennett's gyrodyne had a shaft-driven rotor with torque correction and propulsion for translational flight provided by a side-mounted propeller. Collective pitch of the rotor was a function of, and increased automatically with, shaft torque. During hover and low-speed flight, collective pitch of the propeller was controlled by the pilot with the yaw pedals. As airspeed increased, propeller drag also increased and in order to maintain constant rpm it drew increased power from the engine, which in turn reduced torque at the rotor hub. The latter condition caused an automatic reduction in rotor collective pitch. At cruise airspeed, the rotor operated at autorotative pitch with the tip-path plane parallel to the direction of flight; all propulsion was provided by the propeller. As airspeed was reduced, propeller torque demand decreased which resulted in increased torque at the rotor hub which in turn caused an increase in collective pitch.

Before ca. 1970, the term Gyrodyne exclusively used Bennett's definition. In the helicopter engineering text Aerodynamics of the Helicopter, by Gessow and Myers (1952) we find :

   
Gyrodynes and Heliplanes
 The gyrodyne, a type of helicopter in which the torque counteracting rotor points forward, has the advantage of using the anti-torque rotor instead of the main rotor to pull the machine through the air. This results in more efficient operation of the main rotor in forward flight since it avoids the tilting forward of the rotor and the accompanying radial dissymmetry in blade angle of attack.
   
Gyrodynes and Heliplanes

US Patent 2,317,340 includes provision for a gyrodyne to operate as an autogyro inflight, the aircraft converting from from gyrodyne — not helicopter — to autogyro and back inflight.

[edit] Later development

In later times, Bennett's term gyrodyne was reinterpreted to mean compound gyroplane. This kind of aircraft operates as a helicopter in hover and low-speed flight, and as an autogyro in cruise flight. It does not need a tail rotor, otherwise required in a helicopter to provide a torque to counter the rotating effect of the engine that powers the main rotor, as in models such as the Fairey Aviation FB-1 Gyrodyne the counter-torque was provided from the propellor(s) driving the craft forward. In the subsequent Jet Gyrodyne the rotor was powered by jets at the rotor tips during vertical take-off; the jets coming from compressors powered by the engine rather than directly coupled there was no counter-torque required at all.

It is worth noting that in the early days of helicopters the technology necessary for rotary-wing flight was adopted from the Autogiro. Much of the work in this area was due to the Cierva Autogiro Company, Ltd. (UK) and its partner Autogiro Company of America (US), which undertook fundamental development in rotary-wing theory such as rotor dynamics, cyclic pitch control and collective pitch control. Unlicensed use of Autogiro technology by the US Government resulted in a suit by Harold Pitcairn in 1951 that was settled in 1978 in his favor with the then largest ever award for damages in the United States.

Fairey Rotodyne Type Y Prototype XE521
Enlarge
Fairey Rotodyne Type Y Prototype XE521

The first Fairey Gyrodyne crashed during a high speed test due to hub failure caused by poor machining of a flapping link. The second Gyrodyne, renamed Jet Gyrodyne, was used to develop a pressure-jet rotor drive system with air supplied from the piston-engine powered compressor. At the tip of each stub wing were rearward-facing propellers which provided both yaw control and propulsion in forward flight. Pressure-jet development was led by A.G. Forsyth and August Stepan, the latter working on the Second World War era WN-342 rotor drive system. Though retaining the name Gyrodyne, the Jet Gyrodyne was in fact a compound autogyro. This led to the prototype turboprop powered Fairey Rotodyne. The Rotodyne was developed to combine the efficiency of an aeroplane at cruise with the VTOL capability of a helicopter; it would have served as a short haul airliner from city centres to airports. It had short wings that carried the horizontal flight engines and up to 30% of the aircraft's weight in forward flight. The rotor was driven by tip-mounted jets at take off and landing. Fairey's development efforts were initially led by Bennett, followed by his successor George S. Hislop. Though the Cierva Autogiro Company, Ltd., by then a helicopter company, had been absorbed into Saunders Roe in the early 1950s, later itself acquired by Westland Helicopters, many of its most experienced Autogiro engineers joined Bennett at Fairey where they worked on the Gyrodyne and Rotodyne.

Despite considerable commercial and military interest worldwide in the prototype Type Y Rotodyne for air transport, Fairey decided to develop a larger and more powerful Type Z Rotodyne which, together with withdrawal of British Government support in 1962, resulted in the termination of the project.

An aircraft called a "Heliplane" was built by Kayaba in 1954. It was essentially a Cessna 170 with wings reduced to stubs sufficient to carry the undercarriage and a rotor powered by tip ram-jets.

The McDonnell XV-1, also of the 1950s, was an autogyro with tip jets to give vertical take off. In this case the intention was to create a military aircraft with helicopter VTOL but capable of higher speeds. Two prototypes were built and tested, the first being the first rotary-wing aircraft to make an airborne transition from powered rotor flight to unpowered rotor flight; the second XV-1 became the world's first rotorcraft to exceed 200 mph in level flight on 10 October 1956. The XV-1 project was terminated in 1957.

[edit] Modern developments

The term "Gyrodyne" is no longer used with Bennett's original meaning. The Federal Aviation Administration (FAA) gives the modern legal definition of a Gyrodyne in the USA as a rotor wing aircraft that powers its rotor for takeoff and landing, but en route, flies in autorotation, like a gyroplane, without power to the rotor. Forward thrust is provided by engine driven propellers. Being able to fly in autorotation gives the gyrodyne all of the advantages and simplicity of a gyroplane. Thus, the modern definition of "Gyrodyne" actually describes the wider idea of a "compound gyroplane". To add to this confusion, the Gyrodyne Company of America has also produced a number of coaxial helicopters under the US trademark "Gyrodyne".

FAA Rulemaking Petition number FAA-2006-24170-1 was filed on 10 March 2006 to redefine gyrodyne to its accepted historical and engineering definition, and also to add the terms compound helicopter and compound gyroplane to FAR Part 1: Definitions and Abbrevations.

As with Gyrodyne, the term Heliplane has been redefined from its original use as an advertising term, and given a wider meaning. DARPA are funding a project under the Heliplane name to extend the gyrodyne concept. The new aircraft will use a rotor for take-off and landing vertically, and hovering, together with sustantial wings to provide most of the required lift at cruise. These are hoped to combine the large cargo capacity, fuel efficiency, and high cruise speed of an aeroplane with the VTOL and hovering capabilities of a gyrodyne.

Since 2005, several companies have begun research programs directed at developing a heliplane concept.

Groen Brothers Aviation have concentrated their efforts on developing techniques for converting proven aeroplane designs into gyrodynes; the conversion intended to be a cheaper route than developing aircraft from scratch. Their concept designs have added rotors, trimmed wings (though they are still major structures) and modified tailplanes.

Carter Aviation Technologies have focused on developing technologies with the intention of selling and licensing intellectual property rights developed. Their patents include a high-inertia rotor that allows the aircraft to hover for a short time while unpowered; and the concept of slowing - but not stopping - the rotor at cruise speeds. The rotor is combined with wings that are optimised for high-speed flight only, providing a low-drag configuration.

[edit] Examples

  • Groen Brothers Aviation

[edit] References

  • U.S. Patent 2,317,340: Helicopter. J.A.J.Bennett. 27 April 1943
  • "The Fairey Gyrodyne." J.A.J. Bennett. Journal of the Royal Aeronautical Society, 1949, Vol. 53
  • "Aerodynamics of the Helicopter". Alfred Gessow & Garry C. Myers, Jr. Frederick Ungar Publishing Company, NY. 1952, republished 1962.
  • "Principles of Helicopter Aerodynamics". J. Gordon Leishman, Cambridge University Presss, N.Y. 2000, reprinted 2005.
  • "Principles of Helicopter Engineering". Jacob Shapiro, Temple Press Ltd., London, 1955.
  • "Development of the Autogiro : A Technical Perspective" : J. Gordon Leishman: Hofstra University, New York, 2003.
  • From Autogiro to Gyroplane : The Amazing Survival of an Aviation Technology: Bruce H. Charnov, 2003.

[edit] See also

[edit] External links

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