A compound rotorcraft has both rotary and fixed wings (although in the USA, the term "compound rotorcraft" officially refers to a mixed powerplant system). Some types have a ducted rotor design, in which the rotor is surrounded by a large ring-shaped duct to reduce tip losses. The Ryan XV-5 Vertifan had non-tilt rotors in the wings.
In some designs, such as the Bell Boeing V-22 Osprey, the rotor swings forward to act as a propeller in forward flight. In others, such as the Fairey Rotodyne, a separate method of propulsion is used.
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“Give a scientist a problem and he will probably provide a solution; historians and sociologists, by contrast, can offer only opinions. Ask a dozen chemists the composition of an organic compound such as methane, and within a short time all twelve will have come up with the same solution of CH4. Ask, however, a dozen economists or sociologists to provide policies to reduce unemployment or the level of crime and twelve widely differing opinions are likely to be offered.”
—Derek Gjertsen, British scientist, author. Science and Philosophy: Past and Present, ch. 3, Penguin (1989)