A Gyrodyne is a heavier-than-air aircraft with a rotor system that is normally driven by its engine for takeoff, hovering and landing like a helicopter, but which also has an additional propulsion system that is independent of the rotor system. At higher speeds, the rotor system acts similarly to that of an autogyro, no longer driving the aircraft but simply providing lift.
In recent years a related concept, 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 the United States; Heliplane is an advertising term.
In Russia and Germany, engineers such as 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 Herrick Vertaplane, but cumbersome mechanisms and rotor instability during inflight conversions posed insurmountable problems at the then-current level of technology.
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.
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. 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 or near 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 about 1970, the term Gyrodyne exclusively used Bennett's definition.
US Patent 2,317,340 includes provision for a gyrodyne to operate as an autogyro in flight, the aircraft converting from gyrodyne -- not helicopter -- to autogyro and back in flight.
Helicopter development became practical after the fundamental engineering and practice of the rotary-wing reached an advanced level with 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 pioneering development in rotary-wing theory such as rotor dynamics, cyclic pitch control and collective pitch control. Unlicensed use of Autogiro technology by US Government contractors 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.
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, now rebuilt as the Jet Gyrodyne, was used to develop the pressure-jet rotor drive system. 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 having worked on the Second World War era Doblhoff WN-342 rotor drive system. The Jet Gyrodyne flew in 1954 and made a true transition from vertical to horizontal flight in March 1955. This led to the prototype Fairey Rotodyne which 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 turboprop horizontal flight engines and up to 40% of the aircraft's weight in forward flight. The rotor was driven by tip-jets for take-off and landing and translational flight up to 80 mph.
Fairey's development efforts were initially led by Bennett, followed by his successor Dr. George S. Hislop. Though the Cierva Autogiro Company, Ltd., by then a helicopter company, had been absorbed into Saunders Roe in the early 1950s, 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.
The McDonnell XV-1, also of the 1950s, was a rotorcraft 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.
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. Since 2005, several companies have begun research programs directed at developing a heliplane concept.
Groen Brothers Aviation has concentrated its efforts on developing techniques for converting proven aeroplane designs into gyrodynes; the conversion intended to be a cheaper route than developing aircraft from scratch. The company's concept designs have added rotors, trimmed wings (though they are still major structures) and modified tailplanes.
Carter Aviation Technologies has focused on developing technologies with the intention of selling and licensing the intellectual property rights of the technology. The rotor is combined with wings that are optimised for high-speed flight only, providing a high-speed-low-drag configuration. In 2005 they were able to demonstrate flight with the rotor tip spinning at forward airspeed, without any vibration or control issues occurring. Based on parametric models they estimate a top speed for their aircraft more than twice that of helicopters. Their patents include a winged gyrocopter with 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.
DARPA is 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. Rotor & Wing magazine's February 2007 edition reports that the project is "..a multi-year $40-million, four-phase program. Groen Brothers is working on phase one of that program, a 15-month effort...(it) combines the "gyroplane" ..with a fixed-wing business jet. The team is using the A700, in the very-light-jet class, which was developed by Adam Aircraft Industries.
Gyrodyne as a US trademark was granted to Gyrodyne Company of America, Inc. in 1950. The term gyrodyne was defined by a US Patent 2,317,340, issued in 1943 itself based on a 1939 UK Patent assigned to the Cierva Autogiro Company, Ltd., in which gyrodyne is "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".
The gyrodyne, invented by Cierva Autogiro Company engineer James Allan Jamieson Bennett, is a third distinct type of rotorcraft, the category of aircraft that includes the gyroplane and helicopter. A gyrodyne has a shaft-driven rotor with torque correction and propulsion for translational flight provided by a side-mounted propeller. Collective pitch of the rotor is a function of, and increases automatically with, shaft torque. During hover and low-speed flight, collective pitch of the propeller is controlled by the pilot with the yaw pedals. As airspeed increases, propeller drag also increases and in order to maintain constant rpm it draws increased power from the engine, which in turn reduces torque at the rotor hub. The latter condition causes an automatic reduction in rotor collective pitch. At cruise airspeed, the rotor operates at autorotative pitch with the tip-path plane parallel to the direction of flight; all propulsion is provided by the propeller. As airspeed is reduced, propeller torque demand decreases which results in increased torque at the rotor hub which in turn causes an increase in collective pitch.
Other features included in the definition of gyrodyne include:
1. Low rotor disc loading.
2. Ease of piloting.
3. Compact fuselage.
4. Use of a powered rotor which operates in autorotative pitch in cruise flight.
The Federal Aviation Administration (FAA) in Federal Aviation Regulations, Part 1: Definitions and Abbreviations, defines a gyrodyne as a rotary-wing aircraft that powers its rotor for takeoff, landing and low speed flight, and in cruise flight flies with the rotor in autorotation. Forward thrust is provided by one or more engine driven propellers.
The Fairey Gyrodyne is the only example of a gyrodyne to have been constructed. The second prototype gyrodyne was converted to a compound gyroplane to develop the tip-jet rotor drive system employed on the Fairey Rotodyne "compound gyroplane."