The RAINSTORM Method applies to helicopters having suspended or built-in liquid reservoir. The innovation lies on the transformation of the fire fighting liquid into artificial rain in the form of an umbrella having diameter approximately equal to the diameter of the helicopter's propeller, with adjustable density and duration. The rain creation mechanism in both cases consists of a hollow propeller with two wings where the liquid is guided hydraulically. The liquid jets through nozzles which are in counterpoised arrangement causing the initial revolution of the hollow propeller. This rotation is accelerated and stabilized from the downstream of the helicopter's propeller. The suspended reservoir is adapted by means of a triangular arrangement with three belts through a rectangular stretcher fixed on the helicopter's hook. The built-in reservoir uses a retractable or inclined metallic pipe at the free end of which a hollow propeller is adapted through a free rotation mechanism.