A gyrodyne is a type of VTOL aircraft with a helicopter rotor-like system that needs to be driven by its engine only for takeoff and landing, and includes one or more conventional propeller or jet engines to provide thrust during cruising flight. During forward flight the rotor is unpowered and free-spinning, like an autogyro (but unlike a compound helicopter), and lift is provided by a combination of the rotor and conventional wings. The gyrodyne is one of a number of similar concepts which attempt to combine helicopter-like low-speed performance with conventional fixed-wing high-speeds, including tiltrotors and tiltwings. The gyrodyne was invented by Dr. James Allan Jamieson Bennett as an alternative to the helicopter, in response to an Air Ministry specification. The gyrodyne was envisioned as an intermediate type of rotorcraft, its rotor operating parallel to the flightpath to minimize axial flow with one or more propellers providing propulsion. Bennett's patent covered a variety of designs, which has led to some of the terminological confusion – other issues including the trademarked Gyrodyne Company of America and the Federal Aviation Administration (FAA) classification of rotorcraft. In recent years, a related concept has been promoted under the name heliplane. Originally used to market gyroplanes built by two different companies, the term has been adopted to describe a Defense Advanced Research Projects Agency (DARPA) program to develop advances in rotorcraft technology with the goal of overcoming the current limitations of helicopters in both speed and payload.
Principles of operation Where a conventional helicopter has a powered rotor which provides both lift and forward thrust, and is capable of true VTOL performance, a gyroplane or autogyro has a free-spinning rotor which relies on independent powered thrust to provide forward airspeed and keep it spinning. The gyrodyne combines aspects of each. It has an independent thrust system like the autogyro, but can also drive the rotor to allow vertical takeoff and landing; it then changes to free spinning like an autogyro during cruising flight. In the helicopter, the spinning rotor blades draw air down through the rotor disc; to obtain forward thrust, the rotor disc tilts forward so that air is also blown backwards. In the autogyro the rotor disc is by contrast tilted backwards; as the main thrust drives the craft forwards, air flows through the rotor disc from below, causing it to spin and create lift. The gyrodyne is capable of transitioning between these two modes of flight. Typically a gyrodyne also has fixed wings which provide some of the lift during forward flight, allowing the rotor to be offloaded. A computer simulation has suggested an optimum distribution of lift of 9% for the rotor, and 91% for the wing. However if the rotor is too lightly loaded it can become susceptible to uncontrolled flapping.
History In 1926, with the financial support of Scottish industrialist and aviator James George Weir, Juan de la Cierva founded the Cierva Autogiro Company in the United Kingdom to develop and commercialise his invention the autogyro. Drawing on the autogyro concept, Dr. James Allan Jamieson Bennett, who was promoted to the position of chief technical officer (chief engineer) of the Cierva Autogiro Company following the death of de la Cierva, conceived an intermediate type of rotorcraft in 1936, which he named the gyrodyne, and which was tendered to the British Government in response to an Air Ministry specification that required an aircraft with true vertical flight and hovering capabilities. In 1939, Bennett was issued a patent from the UK Patent Office, assigned to the Cierva Autogiro Company. On 23 August 1940 the Autogiro Company of America, licensees of the Cierva Autogiro Company, Ltd., filed a corresponding patent application in the United States. On 27 April 1943, US patent #2,317,340 was issued to the Autogiro Company of America. The patents describe a gyrodyne as: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. Bennett's concept described a shaft-driven rotor, with anti-torque and propulsion for translational flight provided by one or more propellers mounted on stub wings. With thrust being provided by the propellers at cruise speeds, power would be provided to the rotor only to overcome the profile drag of the rotor, operating in a more efficient manner than the freewheeling rotor of an autogyro in autorotation. Bennett described this flight regime of the gyrodyne as an "intermediate state", requiring power to be supplied to both the rotor and the propulsion system.
Early development The Cierva Autogiro Company Ltd's, C.41 gyrodyne pre-WW2 design study was updated and built by Fairey Aviation as the FB-1 Gyrodyne commencing in 1945. Fairey's development efforts were initially led by Bennett, followed by his successor Dr. George S. Hislop. George B.L. Ellis and Frederick L. Hodgess, engineers from the pre-WW2 Cierva Autogiro Company, Ltd., joined Bennett at Fairey Aviation. The first Fairey Gyrodyne prototype crashed during a test flight, killing the crew. The second Gyrodyne prototype was rebuilt as the Jet Gyrodyne and used to develop a pressure-jet rotor drive system later for the Rotodyne transport compound gyroplane. At the tip of each stub wing were rearward-facing propellers which provided both yaw control and propulsion in forward flight. The Jet Gyrodyne flew in 1954, and made a true transition from vertical to horizontal flight in March 1955.
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