type of apparatus with a rotating wing unit used in meteorology to control the descent of rocket launched radio-sounding instruments, a device or apparatus consisting essentially of a set of freely rotating blades used as a parachute to lower a burden slowly from altitude, the blades being turned by air in the descent, a 'parachute', usually for stores or the recovery of missiles, in which the normal retarding canopy is replaced by rotor blades, which are freely revolving and act like a rotor