The success of the helicopter today is primarily the result of a background of rotary-wing experience covering many years of research into the problems of the gyroplane This simple form of rotorcraft, proposed by JUAN DE LA CIERVA, was developed to a stage at which vertical take-off and landing were normal maneouvres and were no longer exclusive features of the helicopter Only the ability to hover remained as the unique advantage of the power-operated rotor—an advantage for which a heavy penalty had to be paid The general problems of the helicopter for civil use are concerned mainly with an alleviation of the penalty that hovering has incurred