A gyrodyne is a type of VTOL aircraft with a helicopter rotor-like system that is driven by its engine for takeoff and landing only, and includes one or more conventional propeller or jet engines to provide forward 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.
In response to a Royal Navy request for a helicopter, Dr. James Allan Jamieson Bennett designed the gyrodyne whilst serving as the chief engineer of the Cierva Autogiro Company. 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 terminology 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 Britain, Dr. James Allan Jamieson Bennett, Chief Engineer of the Cierva Autogiro Company, conceived an intermediate type of rotorcraft in 1936, which he named "gyrodyne" and which was tendered to the British Government in response to an Air Ministry specification. 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:
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.