Abstract: A compressor or pump employs principles of unsteady delayed stall to enhance the head increase produced by the compressor or pump. Plural airfoil-shaped lifting elements are spaced from each other in a cascade and the fluid is directed into the cascade by a device that varies a parameter of the flow relative to each lifting element in repeating cycles to cause the flow relative to each lifting element to begin to separate from the lifting element and then reattach thereto during each cycle. The cascade can comprise an axial flow impeller with plural impeller blades arranged around a hub capable of rotating on an axis. The device for varying the flow parameter can be a stator with a plurality of stator blades upstream of the impeller, or a second, counter-rotating axial flow impeller. In either case, the parameter is a flow angle at which the flow is directed to the downstream impeller.

Abstract: A fire fighting system uses a bucket suspended from a helicopter to deposit fire retardant onto a fire from an opening in the bottom of the bucket. The bucket has a predetermined configuration and a valve for controlling the area of an opening through which the retardant is deposited when the bucket is suspended from the helicopter. A suitable mechanism, such as an electrically driven valve actuator, varies the area of the opening to deposit the retardant at a volume flow rate as a desired function of time while the helicopter flies along a drop line. The mechanism varies the area of the opening in accordance with a schedule determined before discharge is begun according to the configuration of the bucket, the flow characteristics of the opening as the valve changes the area thereof, and the initial amount of the retardant material in the bucket.