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 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. For example, when the invention is applied to an axial flow compressor, the cascade comprises 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 said 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 propulsor that provides thrust by increasing the velocity of a fluid working medium comprises a rotatable impeller including a plurality of impeller blades spaced from each other, each blade having an airfoil cross-section that provides lift as the fluid working medium travels over it. A stator with plural stator blades directs the fluid working medium into the impeller. The stator blades are arranged to vary a parameter of the flow, such as the flow angle relative to each impeller blade, in repeating cycles in a manner that causes the propulsor to generate a predetermined acoustic signature characterized by predetermined acoustic energy levels in the fluid at given locations spaced from the propulsor. In a preferred form of the propulsor, the flow angle is varied so as to cause the flow relative to each impeller blade to begin to separate and then reattach during each cycle.

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.