Gyrodyne is a VTOL rotorcraft. It has ability to power both rotors and propellers for generating lift and thrust. What makes it of lesser popularity than helicopters. Are there any applications of Gyrodyne?
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The compound helicopter similarly has a separate propulsor for thrust. The gyrodyne differs from it in allowing the lift rotor to autorotate without power during forward flight.
Both are capable of flying faster than a conventional helicopter, while retaining its VTOL abilities. It is thus an attractive idea wherever both high speed and VTOL/hover are required such as military, rescue and executive in-city applications.
However the extra weight and complexity of the thrust system make the already limited, complex and expensive helicopter even more so. Moreover the speed increase over a conventional helicopter is not great enough to be game-changing. Various programmes have led to several prototypes flying, of both gyrodynes and compound helicopters, but there are few if any applications where the high costs and reduced payload justify the modest extra speed over a helicopter.
The Fairey Rotodyne city commute gyrodyne flew but was then cancelled by the UK government.
Several compound helicopters such as the Lockheed Cheyenne have been developed for the US military but then cancelled.
When the USA wanted a fast VTOL military transport, they opted instead for a convertiplane, the Boeing V-22 Osprey. Its speed increase over a conventional helicopter has also turned out to be disappointing.
Maybe one day.
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1$\begingroup$ The noise of the Fairey Rotodyne had to be heard to be believed, apparently. $\endgroup$ May 30, 2020 at 9:50
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$\begingroup$ Indeed. Tipjets need to be cold to be quiet but AFAIK only the French ever got one into production, the Sud-Ouest Djinn helicopter. $\endgroup$ May 30, 2020 at 10:08
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1$\begingroup$ Can a gyrodyne fly much faster than a helicopter, even theoretically? Unlike compound helicopter where the wings take over lift propulsion, in a gyrodyne the rotor still needs to spin, just via autorotation, so the limitiation that advancing blade must not reach critical (transsonic) speed and the retreating blade must move aft fast enough not to stall still applies, does it not? $\endgroup$ Jul 3, 2022 at 18:57
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$\begingroup$ @JanHudec good question, it seems this slanted disk acts as a bad airfoil that generates a lot of induced drag, like for any autogyro. Don't get how it can match conventional heliopters' speed in the first place. $\endgroup$– jkztdJul 4, 2022 at 8:30